Fix M4A fallback ingestion

backend/src/main/java/com/music/config/AsyncConfig.java

@@ -0,0 +1,61 @@
+package com.music.config;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler;
+import org.springframework.aop.interceptor.SimpleAsyncUncaughtExceptionHandler;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.scheduling.annotation.AsyncConfigurer;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
+
+import java.util.concurrent.Executor;
+
+/**
+ * 应用级异步执行配置。
+ *
+ * <p>显式声明名为 {@value #TASK_EXECUTOR_BEAN_NAME} 的 {@link ThreadPoolTaskExecutor}，
+ * 并作为 {@link AsyncConfigurer#getAsyncExecutor()} 的默认 {@code @Async} 执行器。
+ * 这样可消除多个候选 {@code TaskExecutor}（如 WebSocket message broker 通道执行器、
+ * Spring Boot 自动配置的 {@code applicationTaskExecutor}）导致 {@code @Async} 无法选择
+ * 而记录的警告，同时保留任务终态与异常可观测性。</p>
+ *
+ * <p>各 {@code @Async} 方法显式引用 {@value #TASK_EXECUTOR_BEAN_NAME}，
+ * 避免依赖隐式的按类型/按名称解析。</p>
+ */
+@Configuration
+public class AsyncConfig implements AsyncConfigurer {
+
+    private static final Logger log = LoggerFactory.getLogger(AsyncConfig.class);
+
+    /** 应用级异步执行器 bean 名称（供 {@code @Async("...")} 引用） */
+    public static final String TASK_EXECUTOR_BEAN_NAME = "mangtoolTaskExecutor";
+
+    @Bean(name = TASK_EXECUTOR_BEAN_NAME)
+    public ThreadPoolTaskExecutor mangtoolTaskExecutor() {
+        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
+        executor.setCorePoolSize(2);
+        executor.setMaxPoolSize(4);
+        executor.setQueueCapacity(50);
+        executor.setThreadNamePrefix("mangtool-async-");
+        // 关闭时等待正在执行的任务完成，保证任务终态可被观测
+        executor.setWaitForTasksToCompleteOnShutdown(true);
+        executor.setAwaitTerminationSeconds(30);
+        executor.initialize();
+        return executor;
+    }
+
+    @Override
+    public Executor getAsyncExecutor() {
+        return mangtoolTaskExecutor();
+    }
+
+    @Override
+    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
+        return (throwable, method, params) -> {
+            log.error("异步任务 {} 执行抛出未捕获异常", method.getName(), throwable);
+            new SimpleAsyncUncaughtExceptionHandler()
+                    .handleUncaughtException(throwable, method, params);
+        };
+    }
+}

backend/src/main/java/com/music/service/AggregatorService.java

@@ -3,6 +3,7 @@ package com.music.service;
 import com.music.common.FileTransferUtils;
 import com.music.dto.ProgressMessage;
 import org.springframework.messaging.simp.SimpMessagingTemplate;
+import com.music.config.AsyncConfig;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 
@@ -30,7 +31,7 @@ public class AggregatorService {
     /**
      * 异步执行音频文件汇聚任务
      */
-    @Async
+    @Async(AsyncConfig.TASK_EXECUTOR_BEAN_NAME)
     public void aggregate(String taskId, String srcDir, String dstDir, String mode) {
         Path sourcePath = Paths.get(srcDir);
         Path targetPath = Paths.get(dstDir);

backend/src/main/java/com/music/service/AudioValidationService.java

@@ -1,5 +1,7 @@
 package com.music.service;
 
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.stereotype.Component;
@@ -10,7 +12,10 @@ import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -51,11 +56,16 @@ public class AudioValidationService {
     static final int DEFAULT_DECODE_TIMEOUT_SECONDS = 300;
     /** 保留诊断信息最大长度 */
     static final int MAX_DIAGNOSTIC_LENGTH = 512;
+    /** FFprobe 元数据 JSON 输出最大捕获字节数（远大于诊断上限，容纳完整机器可读输出） */
+    static final int MAX_METADATA_JSON_LENGTH = 1024 * 1024;
     /** 流读取缓冲区大小 */
     private static final int BUFFER_SIZE = 4096;
     /** 回收子进程 / 合并 drainer 线程的最长等待秒数 */
     private static final int CLEANUP_WAIT_SECONDS = 5;
 
+    /** 解析 FFprobe 结构化 JSON 输出的线程安全共享实例 */
+    private static final ObjectMapper JSON_MAPPER = new ObjectMapper();
+
     // ========== 嵌套结果类 ==========
 
     /**
@@ -90,6 +100,59 @@ public class AudioValidationService {
         }
     }
 
+    // ========== 嵌套元数据结果类 ==========
+
+    /**
+     * FFprobe 后备元数据读取结果。
+     * <p>{@link #isAvailable()} 表示 FFprobe 成功识别音频流并返回了 format tag 元数据；
+     * 仅在此情况下 {@link #getTags()} 才有意义。字段值均取自 FFprobe 结构化 JSON 输出，
+     * 不做任何文件名猜测或人类可读文本解析。</p>
+     */
+    public static class ProbeMetadata {
+        private final boolean available;
+        private final String diagnostic;
+        private final Map<String, String> tags;
+
+        ProbeMetadata(boolean available, String diagnostic, Map<String, String> tags) {
+            this.available = available;
+            this.diagnostic = diagnostic != null ? diagnostic : "";
+            this.tags = tags != null ? tags : new LinkedHashMap<>();
+        }
+
+        public boolean isAvailable() {
+            return available;
+        }
+
+        public String getDiagnostic() {
+            return diagnostic;
+        }
+
+        /**
+         * 返回小写键 → 值的标签映射（键取自 FFprobe format.tags）。
+         */
+        public Map<String, String> getTags() {
+            return tags;
+        }
+
+        /**
+         * 按候选键列表返回第一个非空标签值（键不区分大小写）。
+         */
+        public String getFirst(String... keys) {
+            for (String key : keys) {
+                if (key == null) continue;
+                String v = tags.get(key.toLowerCase());
+                if (v != null && !v.trim().isEmpty()) {
+                    return v.trim();
+                }
+            }
+            return "";
+        }
+
+        static ProbeMetadata unavailable(String diagnostic) {
+            return new ProbeMetadata(false, diagnostic, null);
+        }
+    }
+
     // ========== 嵌套进程运行结果 ==========
 
     /**
@@ -195,6 +258,116 @@ public class AudioValidationService {
         }
     }
 
+    // ========== 元数据后备读取（FFprobe 结构化 JSON） ==========
+
+    /**
+     * 返回 FFprobe 元数据读取命令参数列表（结构化 JSON 输出，用于测试观察）。
+     * <p>使用 {@code -print_format json} + {@code -show_format} + {@code -show_streams}，
+     * 仅解析机器可读 JSON，绝不解析人类可读文本或文件名。</p>
+     */
+    List<String> getMetadataCommandArgs(Path audioFile) {
+        List<String> cmd = new ArrayList<>();
+        cmd.add(getFfprobeCommand());
+        cmd.add("-v");
+        cmd.add("error");
+        cmd.add("-print_format");
+        cmd.add("json");
+        cmd.add("-show_format");
+        cmd.add("-show_streams");
+        cmd.add(audioFile.toAbsolutePath().toString());
+        return cmd;
+    }
+
+    /**
+     * 使用 FFprobe 结构化 JSON 输出读取音频元数据（jaudiotagger 无法解析时的后备路径）。
+     * <p>要求文件至少含一个可识别的音频流，且能返回 {@code format.tags} 或
+     * {@code streams[].tags}。标签键统一小写化后存入 {@link ProbeMetadata#getTags()}。
+     * 仅解析 JSON，绝不进行文件名猜测或人类可读文本解析。</p>
+     *
+     * @param audioFile 待读取的音频文件路径
+     * @return 后备元数据结果；{@link ProbeMetadata#isAvailable()} 为 false 表示
+     *         FFprobe 无法识别音频或读取失败（调用方应归类为 Unreadable）
+     */
+    public ProbeMetadata readMetadata(Path audioFile) {
+        int timeout = resolveProbeTimeout();
+        ProcessResult result;
+        try {
+            result = runProcess(getMetadataCommandArgs(audioFile), timeout, MAX_METADATA_JSON_LENGTH);
+        } catch (IOException e) {
+            log.warn("FFprobe 元数据读取执行失败: {} - {}", audioFile, e.getMessage());
+            return ProbeMetadata.unavailable("FFprobe 执行失败: " + e.getMessage());
+        }
+
+        if (result.timedOut) {
+            log.warn("FFprobe 元数据读取超时: {} ({}s)", audioFile, timeout);
+            return ProbeMetadata.unavailable("元数据读取超时");
+        }
+        if (result.exitCode != 0) {
+            String diag = capDiagnostic(result.output);
+            log.warn("FFprobe 元数据读取失败: {} (exit={}) diag={}", audioFile, result.exitCode, diag);
+            return ProbeMetadata.unavailable("FFprobe 读取失败: " + diag);
+        }
+
+        try {
+            JsonNode root = JSON_MAPPER.readTree(result.output);
+            if (!hasAudioStream(root)) {
+                log.warn("FFprobe 后备未发现音频流: {}", audioFile);
+                return ProbeMetadata.unavailable("文件中未发现可识别的音频流");
+            }
+
+            Map<String, String> tags = new LinkedHashMap<>();
+            // 优先 format.tags
+            collectTags(root.path("format").path("tags"), tags);
+            // 再补充第一个音频流的 tags（不覆盖已有 format 值）
+            JsonNode streams = root.path("streams");
+            if (streams.isArray()) {
+                for (JsonNode stream : streams) {
+                    if ("audio".equals(stream.path("codec_type").asText())) {
+                        collectTags(stream.path("tags"), tags);
+                        break;
+                    }
+                }
+            }
+            return new ProbeMetadata(true, "", tags);
+        } catch (IOException e) {
+            log.warn("FFprobe JSON 解析失败: {} - {}", audioFile, e.getMessage());
+            return ProbeMetadata.unavailable("FFprobe JSON 解析失败: " + e.getMessage());
+        }
+    }
+
+    /**
+     * 判断 FFprobe JSON 中是否存在音频流。
+     */
+    private static boolean hasAudioStream(JsonNode root) {
+        JsonNode streams = root.path("streams");
+        if (!streams.isArray()) return false;
+        for (JsonNode stream : streams) {
+            if ("audio".equals(stream.path("codec_type").asText())) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * 将 JSON tags 对象的字段收集到映射中（键小写化，已存在的键不覆盖）。
+     */
+    private static void collectTags(JsonNode tagsNode, Map<String, String> target) {
+        if (tagsNode == null || !tagsNode.isObject()) return;
+        Iterator<Map.Entry<String, JsonNode>> fields = tagsNode.fields();
+        while (fields.hasNext()) {
+            Map.Entry<String, JsonNode> entry = fields.next();
+            String key = entry.getKey();
+            if (key == null) continue;
+            String lower = key.toLowerCase();
+            if (target.containsKey(lower)) continue;
+            String value = entry.getValue().asText("");
+            if (value != null && !value.trim().isEmpty()) {
+                target.put(lower, value.trim());
+            }
+        }
+    }
+
     // ========== 解码（FFmpeg，严格模式） ==========
 
     /**
@@ -261,10 +434,20 @@ public class AudioValidationService {
      */
     private static ProcessResult runProcess(List<String> command, int timeoutSeconds)
             throws IOException {
+        return runProcess(command, timeoutSeconds, MAX_DIAGNOSTIC_LENGTH);
+    }
+
+    /**
+     * 运行一个外部进程，并发读取合并后的标准输出，最多保留 {@code maxCapture} 字节。
+     * <p>诊断类调用使用 {@link #MAX_DIAGNOSTIC_LENGTH}；需要完整机器可读输出
+     * （如 FFprobe JSON）时传入更大的上限。超出上限的数据仍被读取以排空管道。</p>
+     */
+    private static ProcessResult runProcess(List<String> command, int timeoutSeconds, int maxCapture)
+            throws IOException {
         ProcessBuilder pb = new ProcessBuilder(command);
         pb.redirectErrorStream(true);
         Process p = pb.start();
-        DrainResult drain = startConcurrentDrainer(p);
+        DrainResult drain = startConcurrentDrainer(p, maxCapture);
 
         boolean interrupted = false;
         boolean finished;
@@ -311,19 +494,19 @@ public class AudioValidationService {
     }
 
     /**
-     * 启动守护线程并发读取进程标准输出（合并后），保留前 {@link #MAX_DIAGNOSTIC_LENGTH}
-     * 字节为诊断信息，继续读取剩余数据以排空管道，防止子进程因管道写满而阻塞或收到 SIGPIPE。
+     * 启动守护线程并发读取进程标准输出（合并后），保留前 {@code maxCapture}
+     * 字节，继续读取剩余数据以排空管道，防止子进程因管道写满而阻塞或收到 SIGPIPE。
      */
-    private static DrainResult startConcurrentDrainer(Process p) {
-        ByteArrayOutputStream buffer = new ByteArrayOutputStream(MAX_DIAGNOSTIC_LENGTH);
+    private static DrainResult startConcurrentDrainer(Process p, int maxCapture) {
+        ByteArrayOutputStream buffer = new ByteArrayOutputStream(Math.min(maxCapture, BUFFER_SIZE));
         Thread t = new Thread(() -> {
             try {
                 byte[] buf = new byte[BUFFER_SIZE];
                 int n;
                 InputStream is = p.getInputStream();
                 while ((n = is.read(buf)) != -1) {
-                    if (buffer.size() < MAX_DIAGNOSTIC_LENGTH) {
-                        int remaining = MAX_DIAGNOSTIC_LENGTH - buffer.size();
+                    if (buffer.size() < maxCapture) {
+                        int remaining = maxCapture - buffer.size();
                         buffer.write(buf, 0, Math.min(n, remaining));
                     }
                     // buffer 已满后继续读取以排空管道，丢弃多余数据

backend/src/main/java/com/music/service/ConvertService.java

@@ -4,6 +4,7 @@ import com.music.dto.ProgressMessage;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.messaging.simp.SimpMessagingTemplate;
+import com.music.config.AsyncConfig;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 
@@ -46,7 +47,7 @@ public class ConvertService {
         this.progressStore = progressStore;
     }
 
-    @Async
+    @Async(AsyncConfig.TASK_EXECUTOR_BEAN_NAME)
     public void convert(String taskId, String srcDir, String dstDir, String mode) {
         Path srcPath = Paths.get(srcDir);
         Path dstPath = Paths.get(dstDir);

backend/src/main/java/com/music/service/DedupService.java

@@ -9,6 +9,7 @@ import org.jaudiotagger.tag.Tag;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.messaging.simp.SimpMessagingTemplate;
+import com.music.config.AsyncConfig;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 
@@ -52,7 +53,7 @@ public class DedupService {
     /**
      * 异步执行去重任务
      */
-    @Async
+    @Async(AsyncConfig.TASK_EXECUTOR_BEAN_NAME)
     public void dedup(String taskId,
                       String libraryDir,
                       String trashDir,

backend/src/main/java/com/music/service/IngestService.java

@@ -12,6 +12,7 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.messaging.simp.SimpMessagingTemplate;
+import com.music.config.AsyncConfig;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 
@@ -77,6 +78,10 @@ public class IngestService {
     private static final int FFMPEG_COMPRESSION_LEVEL = 5;
     private static final int FFMPEG_CHECK_TIMEOUT_SECONDS = 10;
     private static final int FFMPEG_CONVERT_TIMEOUT_SECONDS = 600;
+    /** FFmpeg 合并输出保留的诊断字节上限（超出继续读取以排空管道） */
+    private static final int FFMPEG_DIAGNOSTIC_CAP = 4096;
+    /** 强制终止后回收子进程 / 合并 drainer 的最长等待秒数 */
+    private static final int FFMPEG_CLEANUP_WAIT_SECONDS = 5;
     private static final String FFMPEG_BIN_PROPERTY = "mangtool.ffmpeg.bin";
     private static final String REPORT_SUBDIR = "Reports";
 
@@ -122,7 +127,7 @@ public class IngestService {
      * @param taskId      唯一任务标识
      * @param runningLock 由控制器传入的 AtomicBoolean，任务结束时置为 false
      */
-    @Async
+    @Async(AsyncConfig.TASK_EXECUTOR_BEAN_NAME)
     public void ingest(String taskId, AtomicBoolean runningLock) {
         try {
             String inputDir = configService.getInputDir();
@@ -306,37 +311,76 @@ public class IngestService {
         String fileName = srcFile.getFileName().toString();
         String baseName = getBaseName(fileName);
 
-        // 1. 读取元数据
-        AudioFile audioFile;
-        Tag tag;
+        // 1. 读取元数据：优先 jaudiotagger；受支持的 M4A/MP4 无法解析时回退 FFprobe 结构化输出
+        AudioFile audioFile = null;
+        Tag tag = null;
+        boolean usedFallback = false;
+
+        String title;
+        String artist;
+        String album;
+        String albumArtist;
+        String yearStr;
+        String trackRaw;
+        String discRaw;
+
+        boolean jaudioOk = false;
+        String jaudioError = null;
         try {
             audioFile = AudioFileIO.read(srcFile.toFile());
             tag = audioFile.getTag();
-            if (tag == null) {
-                unreadable.incrementAndGet();
-                moveToRejected(srcFile, rejectedPath, "Unreadable", fileName);
-                return "rejected:unreadable";
+            jaudioOk = (tag != null);
+            if (!jaudioOk) {
+                jaudioError = "标签为空";
             }
         } catch (Exception e) {
-            unreadable.incrementAndGet();
-            moveToRejected(srcFile, rejectedPath, "Unreadable", fileName);
-            log.warn("无法读取文件元数据: {} - {}", fileName, e.getMessage());
-            return "rejected:unreadable";
+            jaudioError = e.getMessage();
         }
 
-        // 2. 读取关键字段
-        String title = trim(tag.getFirst(FieldKey.TITLE));
-        String artist = trim(tag.getFirst(FieldKey.ARTIST));
-        String album = trim(tag.getFirst(FieldKey.ALBUM));
+        if (jaudioOk) {
+            title = trim(tag.getFirst(FieldKey.TITLE));
+            artist = trim(tag.getFirst(FieldKey.ARTIST));
+            album = trim(tag.getFirst(FieldKey.ALBUM));
+            albumArtist = trim(tag.getFirst(FieldKey.ALBUM_ARTIST));
+            yearStr = safeGetFirst(tag, FieldKey.YEAR);
+            trackRaw = safeGetFirst(tag, FieldKey.TRACK);
+            discRaw = safeGetFirst(tag, FieldKey.DISC_NO);
+        } else {
+            // jaudiotagger 无法解析：仅对受支持的 M4A/MP4 且启用了 FFprobe 校验服务时回退
+            if (audioValidationService == null || !isFallbackEligible(srcFile)) {
+                unreadable.incrementAndGet();
+                moveToRejected(srcFile, rejectedPath, "Unreadable", fileName);
+                log.warn("无法读取文件元数据: {} - {}", fileName, jaudioError);
+                return "rejected:unreadable";
+            }
+            AudioValidationService.ProbeMetadata meta = audioValidationService.readMetadata(srcFile);
+            if (!meta.isAvailable()) {
+                unreadable.incrementAndGet();
+                moveToRejected(srcFile, rejectedPath, "Unreadable", fileName);
+                log.warn("FFprobe 后备元数据读取失败: {} - {}", fileName, meta.getDiagnostic());
+                return "rejected:unreadable";
+            }
+            usedFallback = true;
+            title = meta.getFirst("title");
+            artist = meta.getFirst("artist");
+            album = meta.getFirst("album");
+            albumArtist = meta.getFirst("album_artist", "albumartist");
+            yearStr = meta.getFirst("date", "year");
+            trackRaw = meta.getFirst("track");
+            discRaw = meta.getFirst("disc", "discnumber");
+            log.info("jaudiotagger 无法解析，改用 FFprobe 后备读取元数据: {}", fileName);
+        }
 
-        // 3. 校验 Title/Artist/Album 非空
+        // 2. 校验 Title/Artist/Album 非空（任一为空 → MissingMetadata）
         if (title.isEmpty() || artist.isEmpty() || album.isEmpty()) {
             missingMeta.incrementAndGet();
             moveToRejected(srcFile, rejectedPath, "MissingMetadata", fileName);
             return "rejected:missing-metadata";
         }
 
-        // 4. 繁简转换文本标签
+        // 3. 繁简转换文本标签并写回源文件（仅 jaudiotagger 路径；
+        //    FFprobe 后备路径稍后用 FFmpeg 无损 remux 写入简体标签）
+        if (jaudioOk) {
             boolean tagsModified = false;
             for (FieldKey key : TEXT_FIELDS) {
                 String value = trim(tag.getFirst(key));
@@ -348,18 +392,6 @@ public class IngestService {
                     }
                 }
             }
-
-        // 对 albumArtist 也进行繁简转换
-        String albumArtist = trim(tag.getFirst(FieldKey.ALBUM_ARTIST));
-        if (!albumArtist.isEmpty()) {
-            String converted = traditionalFilterService.toSimplified(albumArtist);
-            if (!converted.equals(albumArtist)) {
-                tag.setField(FieldKey.ALBUM_ARTIST, converted);
-                tagsModified = true;
-            }
-        }
-
-        // 5. 将简化后的标签写回源文件
             if (tagsModified) {
                 try {
                     audioFile.commit();
@@ -370,16 +402,12 @@ public class IngestService {
                     return "rejected:tag-write-failed";
                 }
             }
-
-        // 6. 提取其他可选字段（WavTag 等实现可能不支持 YEAR/TRACK/DISC_NO，使用安全读取）
-        String yearStr = safeGetFirst(tag, FieldKey.YEAR);
-        String trackRaw = safeGetFirst(tag, FieldKey.TRACK);
-        String discRaw = safeGetFirst(tag, FieldKey.DISC_NO);
+        }
 
         int trackNum = parseInt(trackRaw, 0);
         int discNum = parseInt(discRaw, 0);
 
-        // 7. 计算 MD5 用于去重兜底
+        // 4. 计算 MD5 用于去重兜底
         String fileMd5 = computeMd5(srcFile);
 
         // 8. 构建归一化身份标识
@@ -399,7 +427,7 @@ public class IngestService {
             return "rejected:duplicate";
         }
 
-        // 10. 格式转换（如需要）
+        // 5. 格式转换 / 后备 remux（如需要）
         Path effectiveFile = srcFile;
         boolean needsConversion = isLosslessFormat(srcFile);
         if (needsConversion) {
@@ -412,13 +440,33 @@ public class IngestService {
                 log.warn("转码失败: {} - {}", fileName, e.getMessage());
                 return "rejected:conversion-failed";
             }
+        } else if (usedFallback) {
+            // jaudiotagger 无法写回此容器的标签：用 FFmpeg 无损 remux（-c copy）
+            // 生成保留音频质量与原有元数据的 Navidrome 兼容输出，并写入简体 Title/Artist/Album。
+            String simpTitle = traditionalFilterService.toSimplified(title);
+            String simpArtist = traditionalFilterService.toSimplified(artist);
+            String simpAlbum = traditionalFilterService.toSimplified(album);
+            String simpAlbumArtist = albumArtist.isEmpty()
+                    ? "" : traditionalFilterService.toSimplified(albumArtist);
+            try {
+                Path remuxed = remuxWithSimplifiedTags(srcFile, simpTitle, simpArtist,
+                        simpAlbum, simpAlbumArtist);
+                effectiveFile = remuxed;
+            } catch (Exception e) {
+                convFailed.incrementAndGet();
+                moveToRejected(srcFile, rejectedPath, "ConversionFailed", fileName);
+                log.warn("后备 remux 失败: {} - {}", fileName, e.getMessage());
+                return "rejected:conversion-failed";
+            }
         }
 
-        // 11. 音频完整性验证：确保有效文件可被 FFprobe 识别且 FFmpeg 可完整解码
+        boolean derivedFile = !effectiveFile.equals(srcFile);
+
+        // 6. 音频完整性验证：确保有效文件可被 FFprobe 识别且 FFmpeg 可完整解码
         if (audioValidationService != null) {
             ValidationResult vr = audioValidationService.validate(effectiveFile);
             if (!vr.isValid()) {
-                if (needsConversion && !effectiveFile.equals(srcFile)) {
+                if (derivedFile) {
                     deleteIfExists(effectiveFile);
                 }
                 unreadable.incrementAndGet();
@@ -428,9 +476,35 @@ public class IngestService {
             }
         }
 
-        // 12. 重新打开有效文件，重新检查 Title/Artist/Album
-        //     （确保转换过程或标签持久化未导致 Navidrome 必需的元数据丢失）
+        // 7. 重新检查有效文件的 Title/Artist/Album（确保转换/remux/标签持久化未丢失必需元数据）
         if (audioValidationService != null) {
+            if (usedFallback) {
+                // 后备路径：jaudiotagger 仍无法解析该容器，改用 FFprobe 再次读取校验
+                AudioValidationService.ProbeMetadata reMeta =
+                        audioValidationService.readMetadata(effectiveFile);
+                String vTitle = reMeta.isAvailable() ? reMeta.getFirst("title") : "";
+                String vArtist = reMeta.isAvailable() ? reMeta.getFirst("artist") : "";
+                String vAlbum = reMeta.isAvailable() ? reMeta.getFirst("album") : "";
+                if (vTitle.isEmpty() || vArtist.isEmpty() || vAlbum.isEmpty()) {
+                    if (derivedFile) {
+                        deleteIfExists(effectiveFile);
+                    }
+                    unreadable.incrementAndGet();
+                    moveToRejected(srcFile, rejectedPath, "Unreadable", fileName);
+                    log.warn("后备 remux 后元数据缺失: {}（Title='{}' Artist='{}' Album='{}'）",
+                            fileName, vTitle, vArtist, vAlbum);
+                    return "rejected:unreadable";
+                }
+                title = vTitle;
+                artist = vArtist;
+                album = vAlbum;
+                albumArtist = reMeta.getFirst("album_artist", "albumartist");
+                yearStr = reMeta.getFirst("date", "year");
+                trackRaw = reMeta.getFirst("track");
+                discRaw = reMeta.getFirst("disc", "discnumber");
+                trackNum = parseInt(trackRaw, 0);
+                discNum = parseInt(discRaw, 0);
+            } else {
                 try {
                     AudioFile validatedAudio = AudioFileIO.read(effectiveFile.toFile());
                     Tag validatedTag = validatedAudio.getTag();
@@ -438,7 +512,7 @@ public class IngestService {
                     String vArtist = trim(validatedTag != null ? validatedTag.getFirst(FieldKey.ARTIST) : "");
                     String vAlbum = trim(validatedTag != null ? validatedTag.getFirst(FieldKey.ALBUM) : "");
                     if (vTitle.isEmpty() || vArtist.isEmpty() || vAlbum.isEmpty()) {
-                    if (needsConversion && !effectiveFile.equals(srcFile)) {
+                        if (derivedFile) {
                             deleteIfExists(effectiveFile);
                         }
                         unreadable.incrementAndGet();
@@ -459,7 +533,7 @@ public class IngestService {
                     trackNum = parseInt(trackRaw, 0);
                     discNum = parseInt(discRaw, 0);
                 } catch (Exception e) {
-                if (needsConversion && !effectiveFile.equals(srcFile)) {
+                    if (derivedFile) {
                         deleteIfExists(effectiveFile);
                     }
                     unreadable.incrementAndGet();
@@ -468,10 +542,18 @@ public class IngestService {
                     return "rejected:unreadable";
                 }
             }
+        }
 
-        // 13. 确定最终格式与文件名
-        String ext = needsConversion ? "flac" : getExtension(fileName);
+        // 确定最终格式与文件名（后备 remux 统一输出 m4a 容器）
+        String ext;
+        if (needsConversion) {
+            ext = "flac";
+        } else if (usedFallback) {
+            ext = "m4a";
+        } else {
+            ext = getExtension(fileName);
             if (ext == null) ext = "flac";
+        }
 
         // 12. 构建目标路径
         String effectiveArtist = !albumArtist.isEmpty()
@@ -491,40 +573,39 @@ public class IngestService {
         String destFileName = trackStr + " - " + safeTitle + "." + ext;
         Path targetFile = resolveUniqueFile(targetDir, destFileName);
 
-        // 13. 移动/复制到目标位置
+        // 8. 移动/复制到目标位置
         try {
             FileTransferUtils.moveWithFallback(effectiveFile, targetFile);
         } catch (IOException e) {
             otherRejected.incrementAndGet();
-            // 如果经过转换，删除临时 FLAC 并隔离源文件
-            if (needsConversion && !effectiveFile.equals(srcFile)) {
+            // 如果经过转换/remux，删除派生文件并隔离源文件
+            if (derivedFile) {
                 deleteIfExists(effectiveFile);
-                moveToRejected(srcFile, rejectedPath, "Other", fileName);
-            } else {
-                moveToRejected(srcFile, rejectedPath, "Other", fileName);
             }
+            moveToRejected(srcFile, rejectedPath, "Other", fileName);
             log.warn("移动文件到 Library 失败: {} - {}", fileName, e.getMessage());
             return "rejected:move-failed";
         }
 
-        // 14. 如果进行了格式转换且成功，删除原文件
-        if (needsConversion && !effectiveFile.equals(srcFile)) {
+        // 9. 如果生成了派生文件（转换或后备 remux）且成功，删除原文件
+        if (derivedFile) {
             deleteIfExists(srcFile);
         }
 
-        // 15. 更新身份标识集合
+        // 10. 更新身份标识集合
         libraryIdentities.add(identity);
         batchIdentities.add(identity);
         ingested.incrementAndGet();
 
-        // 16. 处理关联 LRC 文件（可选）
+        // 11. 处理关联 LRC 文件（可选）
         handleAssociatedLrc(srcFile, targetDir, baseName, destFileName);
 
-        // 17. 提取嵌入式歌词（可选）写入 LRC
+        // 12. 提取嵌入式歌词与封面（可选，仅 jaudiotagger 路径有 tag 对象；
+        //     后备 remux 已保留原始嵌入式封面/歌词于输出容器中）
+        if (tag != null) {
             extractEmbeddedLyrics(tag, targetDir, trackStr, safeTitle, title, effectiveArtist);
-
-        // 18. 提取封面（可选）
             extractCover(tag, targetDir);
+        }
 
         return "ingested";
     }
@@ -732,30 +813,19 @@ public class IngestService {
         Path output = outputDir.resolve(baseName + ".flac");
         output = resolveUniqueFile(outputDir, baseName + ".flac");
 
-        ProcessBuilder pb = new ProcessBuilder(
+        List<String> cmd = new ArrayList<>(Arrays.asList(
                 getFfmpegCommand(),
                 "-y",
                 "-i", input.toAbsolutePath().toString(),
                 "-compression_level", String.valueOf(FFMPEG_COMPRESSION_LEVEL),
                 output.toAbsolutePath().toString()
-        );
-        pb.redirectErrorStream(true);
-        Process p = pb.start();
-        boolean finished = p.waitFor(FFMPEG_CONVERT_TIMEOUT_SECONDS, TimeUnit.SECONDS);
-        if (!finished) {
-            p.destroyForcibly();
-            deleteIfExists(output);
-            throw new RuntimeException("ffmpeg 转码超时（" + FFMPEG_CONVERT_TIMEOUT_SECONDS + "s）");
-        }
-        int exit = p.exitValue();
-        if (exit != 0) {
-            deleteIfExists(output);
-            throw new RuntimeException("ffmpeg 退出码: " + exit);
-        }
+        ));
+        runFfmpegDrained(cmd, FFMPEG_CONVERT_TIMEOUT_SECONDS, output, "转码");
         return output;
     }
 
     private void deleteIfExists(Path path) {
+        if (path == null) return;
         try {
             Files.deleteIfExists(path);
         } catch (IOException e) {
@@ -763,6 +833,159 @@ public class IngestService {
         }
     }
 
+    /** FFprobe 后备读取仅对这些容器格式启用（jaudiotagger 常拒绝的合法 AAC/M4A/MP4） */
+    private static final Set<String> FALLBACK_ELIGIBLE_EXTENSIONS = new HashSet<>(Arrays.asList(
+            "m4a", "mp4", "aac", "m4b", "m4p"
+    ));
+
+    /**
+     * 判断文件是否适用 FFprobe 元数据后备读取路径。
+     * 仅限受支持的 M4A/MP4/AAC 容器，避免对其他格式做无意义的后备。
+     */
+    private boolean isFallbackEligible(Path file) {
+        String ext = getExtension(file.getFileName().toString());
+        return ext != null && FALLBACK_ELIGIBLE_EXTENSIONS.contains(ext);
+    }
+
+    /**
+     * 使用 FFmpeg 无损 remux（{@code -c copy}）生成保留音频质量与原有元数据的
+     * Navidrome 兼容 M4A 输出，并写入简体 Title/Artist/Album（及可选 Album Artist）。
+     * <p>用于 jaudiotagger 无法安全写回该容器标签、且不能修改原文件的场景，
+     * 避免因写回失败而误拒绝合法音频。不伪造缺失的必要元数据。</p>
+     * <p>输出为独立临时文件；调用方负责在失败或验证不通过时清理。</p>
+     *
+     * @return 生成的 M4A 输出路径
+     */
+    List<String> buildRemuxCommand(Path input, Path output, String title, String artist,
+                                   String album, String albumArtist) {
+        List<String> cmd = new ArrayList<>();
+        cmd.add(getFfmpegCommand());
+        cmd.add("-y");
+        cmd.add("-i");
+        cmd.add(input.toAbsolutePath().toString());
+        // 仅映射预期的第一个音频流，避免把普通视频/字幕/数据等流带入生成的 M4A，
+        // 确保输出是干净的 Navidrome 兼容音乐资产。
+        cmd.add("-map");
+        cmd.add("0:a:0");
+        cmd.add("-c");
+        cmd.add("copy");
+        // 保留原有 format 级元数据（不含未映射的流），随后覆盖简体标签
+        cmd.add("-map_metadata");
+        cmd.add("0");
+        // 覆盖简体标签（不伪造缺失字段：调用方已确保三项必需字段非空）
+        cmd.add("-metadata");
+        cmd.add("title=" + title);
+        cmd.add("-metadata");
+        cmd.add("artist=" + artist);
+        cmd.add("-metadata");
+        cmd.add("album=" + album);
+        if (albumArtist != null && !albumArtist.isEmpty()) {
+            cmd.add("-metadata");
+            cmd.add("album_artist=" + albumArtist);
+        }
+        cmd.add(output.toAbsolutePath().toString());
+        return cmd;
+    }
+
+    private Path remuxWithSimplifiedTags(Path input, String title, String artist,
+                                         String album, String albumArtist)
+            throws IOException, InterruptedException {
+        String baseName = getBaseName(input.getFileName().toString());
+        Path output = resolveUniqueFile(input.getParent(), baseName + ".fallback.m4a");
+
+        List<String> cmd = buildRemuxCommand(input, output, title, artist, album, albumArtist);
+        runFfmpegDrained(cmd, FFMPEG_CONVERT_TIMEOUT_SECONDS, output, "remux");
+        return output;
+    }
+
+    /**
+     * 运行一个 FFmpeg 子进程，并发排空其合并后的标准输出，避免管道写满导致死锁；
+     * 超时或中断时强制终止并有界回收，失败时清理输出文件。
+     * <p>合并 stderr→stdout 后由守护线程持续读取（仅保留前 {@value #FFMPEG_DIAGNOSTIC_CAP}
+     * 字节作诊断），超出部分丢弃以排空管道。非零退出或超时抛出 {@link RuntimeException}。</p>
+     *
+     * @param command        完整命令行
+     * @param timeoutSeconds 超时秒数
+     * @param outputToClean  失败/超时时需要删除的输出文件（可为 null）
+     * @param label          日志/异常用的操作标签（如 "remux" / "转码"）
+     */
+    private void runFfmpegDrained(List<String> command, int timeoutSeconds,
+                                  Path outputToClean, String label)
+            throws IOException, InterruptedException {
+        ProcessBuilder pb = new ProcessBuilder(command);
+        pb.redirectErrorStream(true);
+        Process p = pb.start();
+
+        final StringBuilder diag = new StringBuilder();
+        Thread drainer = new Thread(() -> {
+            try (InputStream is = p.getInputStream()) {
+                byte[] buf = new byte[4096];
+                int n;
+                while ((n = is.read(buf)) != -1) {
+                    synchronized (diag) {
+                        int remaining = FFMPEG_DIAGNOSTIC_CAP - diag.length();
+                        if (remaining > 0) {
+                            diag.append(new String(buf, 0, Math.min(n, remaining),
+                                    StandardCharsets.UTF_8));
+                        }
+                        // 已达上限后继续读取以排空管道，丢弃多余数据
+                    }
+                }
+            } catch (IOException ignored) {
+                // 进程终止后流关闭属正常情况
+            }
+        }, "ffmpeg-" + label + "-drainer");
+        drainer.setDaemon(true);
+        drainer.start();
+
+        boolean interrupted = false;
+        boolean finished;
+        try {
+            finished = p.waitFor(timeoutSeconds, TimeUnit.SECONDS);
+        } catch (InterruptedException e) {
+            interrupted = true;
+            finished = false;
+        }
+
+        if (!finished) {
+            p.destroyForcibly();
+            try {
+                p.waitFor(FFMPEG_CLEANUP_WAIT_SECONDS, TimeUnit.SECONDS);
+            } catch (InterruptedException e) {
+                interrupted = true;
+            }
+        }
+
+        // 先 join drainer 确保输出读尽，再判定结果
+        try {
+            drainer.join(TimeUnit.SECONDS.toMillis(FFMPEG_CLEANUP_WAIT_SECONDS));
+        } catch (InterruptedException e) {
+            interrupted = true;
+        }
+
+        if (interrupted) {
+            deleteIfExists(outputToClean);
+            Thread.currentThread().interrupt();
+            throw new InterruptedException("ffmpeg " + label + " 被中断");
+        }
+
+        if (!finished) {
+            deleteIfExists(outputToClean);
+            throw new RuntimeException("ffmpeg " + label + " 超时（" + timeoutSeconds + "s）");
+        }
+
+        int exit = p.exitValue();
+        if (exit != 0) {
+            String tail;
+            synchronized (diag) {
+                tail = diag.toString().trim();
+            }
+            deleteIfExists(outputToClean);
+            throw new RuntimeException("ffmpeg " + label + " 退出码: " + exit
+                    + (tail.isEmpty() ? "" : " - " + tail));
+        }
+    }
+
     /**
      * 扫描 Library 目录中已有的音频文件，构建身份标识集合
      * （所有文本字段经过 t2s + lowercase 归一化，与 incoming 文件一致）

backend/src/main/java/com/music/service/LibraryMergeService.java

@@ -5,6 +5,7 @@ import com.music.dto.ProgressMessage;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.messaging.simp.SimpMessagingTemplate;
+import com.music.config.AsyncConfig;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 
@@ -42,7 +43,7 @@ public class LibraryMergeService {
         this.progressStore = progressStore;
     }
 
-    @Async
+    @Async(AsyncConfig.TASK_EXECUTOR_BEAN_NAME)
     public void merge(String taskId, String srcDir, String dstDir, boolean smartUpgrade, boolean keepBackup) {
         Path srcPath = Paths.get(srcDir);
         Path dstPath = Paths.get(dstDir);

backend/src/main/java/com/music/service/OrganizeService.java

@@ -16,6 +16,7 @@ import org.jaudiotagger.tag.flac.FlacTag;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.messaging.simp.SimpMessagingTemplate;
+import com.music.config.AsyncConfig;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 
@@ -66,7 +67,7 @@ public class OrganizeService {
         this.pinyinFormat.setToneType(HanyuPinyinToneType.WITHOUT_TONE);
     }
 
-    @Async
+    @Async(AsyncConfig.TASK_EXECUTOR_BEAN_NAME)
     public void organize(String taskId, String srcDir, String dstDir, String mode,
                          boolean extractCover, boolean extractLyrics, boolean generateReport) {
         Path srcPath = Paths.get(srcDir);

backend/src/main/java/com/music/service/ZhConvertService.java

@@ -10,6 +10,7 @@ import org.jaudiotagger.tag.Tag;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.messaging.simp.SimpMessagingTemplate;
+import com.music.config.AsyncConfig;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 
@@ -64,7 +65,7 @@ public class ZhConvertService {
      * @param mode           preview / execute
      * @param thresholdRatio 触发阈值（0.0-1.0）
      */
-    @Async
+    @Async(AsyncConfig.TASK_EXECUTOR_BEAN_NAME)
     public void process(String taskId,
                         String scanDir,
                         String outputDir,

backend/src/test/java/com/music/config/AsyncConfigTest.java

@@ -0,0 +1,72 @@
+package com.music.config;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
+
+import java.lang.reflect.Method;
+import java.util.concurrent.Executor;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * {@link AsyncConfig} 单元测试：验证 {@code @Async} 使用明确的应用 taskExecutor，
+ * 从而消除多个 TaskExecutor 无法选择的警告，并保留异常处理器。
+ */
+class AsyncConfigTest {
+
+    private final AsyncConfig config = new AsyncConfig();
+
+    @Test
+    void taskExecutorBeanIsConfiguredThreadPool() {
+        ThreadPoolTaskExecutor executor = config.mangtoolTaskExecutor();
+        assertNotNull(executor);
+        assertEquals("mangtool-async-", executor.getThreadNamePrefix());
+        assertTrue(executor.getCorePoolSize() >= 1);
+        assertTrue(executor.getMaxPoolSize() >= executor.getCorePoolSize());
+        executor.shutdown();
+    }
+
+    @Test
+    void getAsyncExecutorReturnsExplicitExecutor() {
+        Executor executor = config.getAsyncExecutor();
+        assertNotNull(executor, "@Async 应有明确的默认执行器，避免多候选无法选择");
+        assertTrue(executor instanceof ThreadPoolTaskExecutor);
+        ((ThreadPoolTaskExecutor) executor).shutdown();
+    }
+
+    @Test
+    void getAsyncUncaughtExceptionHandlerPresent() {
+        assertNotNull(config.getAsyncUncaughtExceptionHandler(),
+                "应提供异常处理器以保留异步任务异常可观测性");
+    }
+
+    @Test
+    void beanNameConstantMatchesFactoryMethod() throws Exception {
+        // @Bean 方法名即 bean 名称，需与供 @Async 引用的常量一致
+        Method m = AsyncConfig.class.getMethod(AsyncConfig.TASK_EXECUTOR_BEAN_NAME);
+        assertNotNull(m, "bean 名称常量应对应工厂方法名: " + AsyncConfig.TASK_EXECUTOR_BEAN_NAME);
+    }
+
+    @Test
+    void asyncAnnotationsReferenceExplicitExecutor() {
+        // 抽查关键的 @Async 服务方法，确认显式引用了应用级 executor
+        assertAsyncQualifier(com.music.service.IngestService.class, "ingest");
+        assertAsyncQualifier(com.music.service.ConvertService.class, "convert");
+    }
+
+    private static void assertAsyncQualifier(Class<?> serviceClass, String methodName) {
+        Method target = null;
+        for (Method m : serviceClass.getDeclaredMethods()) {
+            if (m.getName().equals(methodName)) {
+                target = m;
+                break;
+            }
+        }
+        assertNotNull(target, "应找到方法 " + methodName);
+        org.springframework.scheduling.annotation.Async async =
+                target.getAnnotation(org.springframework.scheduling.annotation.Async.class);
+        assertNotNull(async, methodName + " 应带 @Async 注解");
+        assertEquals(AsyncConfig.TASK_EXECUTOR_BEAN_NAME, async.value(),
+                methodName + " 的 @Async 应显式引用应用级 taskExecutor");
+    }
+}

backend/src/test/java/com/music/service/AudioValidationServiceTest.java

@@ -10,6 +10,7 @@ import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
@@ -436,6 +437,115 @@ class AudioValidationServiceTest {
         }
     }
 
+    // ========== FFprobe 后备元数据读取 ==========
+
+    @Test
+    void getMetadataCommandArgs_usesStructuredJson() {
+        Path f = Paths.get("/tmp/song.m4a");
+        List<String> args = service.getMetadataCommandArgs(f);
+        assertTrue(args.contains("-print_format"));
+        assertTrue(args.contains("json"));
+        assertTrue(args.contains("-show_format"));
+        assertTrue(args.contains("-show_streams"));
+        // 绝不使用任何人类可读文本或文件名猜测选项
+        assertFalse(args.contains("-of"));
+        assertEquals(f.toAbsolutePath().toString(), args.get(args.size() - 1));
+    }
+
+    @Test
+    void readMetadata_returnsFullTags() throws Exception {
+        assumeFfmpegFfprobe();
+        Path tmpDir = Files.createTempDirectory("probe-meta-");
+        try {
+            Path m4a = createTaggedM4a(tmpDir, "song.m4a",
+                    "ProbeTitle", "ProbeArtist", "ProbeAlbum");
+
+            AudioValidationService.ProbeMetadata meta = service.readMetadata(m4a);
+            assertTrue(meta.isAvailable(), "应成功读取元数据");
+            assertEquals("ProbeTitle", meta.getFirst("title"));
+            assertEquals("ProbeArtist", meta.getFirst("artist"));
+            assertEquals("ProbeAlbum", meta.getFirst("album"));
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void readMetadata_missingAlbumReturnsEmpty() throws Exception {
+        assumeFfmpegFfprobe();
+        Path tmpDir = Files.createTempDirectory("probe-meta-");
+        try {
+            // 仅写 title/artist，故意不写 album
+            Path m4a = tmpDir.resolve("noalbum.m4a");
+            ProcessBuilder pb = new ProcessBuilder(
+                    "ffmpeg", "-y", "-f", "lavfi", "-i", "anullsrc=r=44100:cl=mono",
+                    "-t", "0.3", "-c:a", "aac",
+                    "-metadata", "title=T", "-metadata", "artist=A",
+                    m4a.toAbsolutePath().toString());
+            pb.redirectErrorStream(true);
+            Process p = pb.start();
+            readAllBytes(p.getInputStream());
+            p.waitFor(15, TimeUnit.SECONDS);
+
+            AudioValidationService.ProbeMetadata meta = service.readMetadata(m4a);
+            assertTrue(meta.isAvailable());
+            assertEquals("", meta.getFirst("album"), "缺失的 album 应返回空字符串");
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void readMetadata_nonAudioFileUnavailable() throws Exception {
+        assumeFfmpegFfprobe();
+        Path tmpDir = Files.createTempDirectory("probe-meta-");
+        try {
+            Path bogus = tmpDir.resolve("bogus.m4a");
+            Files.write(bogus, "not an audio file".getBytes(StandardCharsets.UTF_8));
+
+            AudioValidationService.ProbeMetadata meta = service.readMetadata(bogus);
+            assertFalse(meta.isAvailable(), "无法识别的文件应返回 unavailable");
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void readMetadata_ffprobeFailureUnavailable() {
+        // 强制 ffprobe 指向失败命令
+        System.setProperty(AudioValidationService.FFPROBE_BIN_PROPERTY, "/bin/false");
+        AudioValidationService.ProbeMetadata meta =
+                service.readMetadata(Paths.get("/tmp/whatever.m4a"));
+        assertFalse(meta.isAvailable(), "ffprobe 失败应返回 unavailable");
+    }
+
+    /**
+     * 使用 FFmpeg 创建一个带标签的有效短 M4A（AAC）文件。
+     */
+    private static Path createTaggedM4a(Path dir, String fileName,
+                                        String title, String artist, String album) throws Exception {
+        Path out = dir.resolve(fileName);
+        ProcessBuilder pb = new ProcessBuilder(
+                "ffmpeg", "-y", "-f", "lavfi", "-i", "anullsrc=r=44100:cl=mono",
+                "-t", "0.3", "-c:a", "aac",
+                "-metadata", "title=" + title,
+                "-metadata", "artist=" + artist,
+                "-metadata", "album=" + album,
+                out.toAbsolutePath().toString());
+        pb.redirectErrorStream(true);
+        Process p = pb.start();
+        readAllBytes(p.getInputStream());
+        boolean finished = p.waitFor(15, TimeUnit.SECONDS);
+        if (!finished) {
+            p.destroyForcibly();
+            throw new RuntimeException("ffmpeg 创建 M4A 超时");
+        }
+        if (p.exitValue() != 0) {
+            throw new RuntimeException("ffmpeg 创建 M4A 失败 (exit=" + p.exitValue() + ")");
+        }
+        return out;
+    }
+
     // ========== 帮助方法 ==========
 
     /**

backend/src/test/java/com/music/service/IngestServiceE2ETest.java

@@ -18,6 +18,7 @@ import java.lang.reflect.Method;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
@@ -28,8 +29,11 @@ import java.util.stream.Stream;
 
 import static org.junit.jupiter.api.Assertions.*;
 import static org.junit.jupiter.api.Assumptions.assumeTrue;
+import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.when;
+import static org.mockito.ArgumentMatchers.any;
 
 /**
  * 一键导入服务端到端测试 —— 使用临时文件系统验证完整的导入管线行为。
@@ -1210,8 +1214,447 @@ class IngestServiceE2ETest {
         }
     }
 
+    // ========== 5. FFprobe 元数据后备（jaudiotagger 无法解析的合法 M4A/AAC） ==========
+
+    @Test
+    void jaudiotaggerUnreadableM4a_ffprobeFallbackIngested() throws Exception {
+        assumeFfmpeg();
+        Path tmpDir = Files.createTempDirectory("ingest-fallback-");
+        try {
+            Path inputDir = tmpDir.resolve("Input");
+            Path libDir = tmpDir.resolve("Library");
+            Path rejDir = tmpDir.resolve("Rejected");
+            Files.createDirectories(inputDir);
+            Files.createDirectories(libDir);
+            Files.createDirectories(rejDir);
+
+            // M4A 容器但扩展名为 .aac → jaudiotagger 无 AAC reader 而拒绝，
+            // FFprobe 能内容探测并读取完整 Title/Artist/Album
+            Path src = createMp4ContainerAsAac(inputDir, "legit.aac",
+                    "Fb Title", "Fb Artist", "Fb Album");
+            assertJaudiotaggerCannotRead(src);
+
+            IngestService service = buildServiceWithValidation();
+            AtomicInteger ingested = new AtomicInteger();
+            AtomicInteger duplicates = new AtomicInteger();
+            AtomicInteger missingMeta = new AtomicInteger();
+            AtomicInteger unreadable = new AtomicInteger();
+            AtomicInteger convFailed = new AtomicInteger();
+            AtomicInteger otherRejected = new AtomicInteger();
+
+            String result = invokeProcessSingleFile(service, src, libDir, rejDir,
+                    new HashSet<>(), new HashSet<>(),
+                    ingested, duplicates, missingMeta, unreadable,
+                    convFailed, otherRejected);
+
+            assertEquals("ingested", result,
+                    "jaudiotagger 无法解析但 FFprobe 提供完整元数据的 M4A 应入库");
+            assertEquals(1, ingested.get());
+            assertEquals(0, unreadable.get());
+            assertEquals(0, missingMeta.get());
+
+            Path expectedDir = libDir.resolve("Fb Artist").resolve("Fb Album");
+            assertTrue(Files.isDirectory(expectedDir), "应创建 Artist/Album 目录");
+            boolean found = Files.list(expectedDir).anyMatch(p ->
+                    p.getFileName().toString().equals("01 - Fb Title.m4a"));
+            assertTrue(found, "后备 remux 输出应为 01 - Fb Title.m4a");
+            assertFalse(Files.exists(src), "源文件应在 remux 后被删除");
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void jaudiotaggerUnreadableM4a_missingAlbumRejectedMissingMetadata() throws Exception {
+        assumeFfmpeg();
+        Path tmpDir = Files.createTempDirectory("ingest-fallback-");
+        try {
+            Path inputDir = tmpDir.resolve("Input");
+            Path libDir = tmpDir.resolve("Library");
+            Path rejDir = tmpDir.resolve("Rejected");
+            Files.createDirectories(inputDir);
+            Files.createDirectories(libDir);
+            Files.createDirectories(rejDir);
+
+            // 仅 title/artist，无 album → 后备读取后仍应归类 MissingMetadata
+            Path src = createMp4ContainerAsAac(inputDir, "noalbum.aac",
+                    "Only Title", "Only Artist", null);
+            assertJaudiotaggerCannotRead(src);
+
+            IngestService service = buildServiceWithValidation();
+            AtomicInteger ingested = new AtomicInteger();
+            AtomicInteger duplicates = new AtomicInteger();
+            AtomicInteger missingMeta = new AtomicInteger();
+            AtomicInteger unreadable = new AtomicInteger();
+            AtomicInteger convFailed = new AtomicInteger();
+            AtomicInteger otherRejected = new AtomicInteger();
+
+            String result = invokeProcessSingleFile(service, src, libDir, rejDir,
+                    new HashSet<>(), new HashSet<>(),
+                    ingested, duplicates, missingMeta, unreadable,
+                    convFailed, otherRejected);
+
+            assertEquals("rejected:missing-metadata", result,
+                    "后备读取缺 Album 应归类 MissingMetadata");
+            assertEquals(1, missingMeta.get());
+            assertEquals(0, unreadable.get());
+            assertTrue(Files.exists(rejDir.resolve("MissingMetadata").resolve("noalbum.aac")));
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void jaudiotaggerUnreadable_ffprobeAlsoFails_rejectedUnreadable() throws Exception {
+        assumeFfmpeg();
+        Path tmpDir = Files.createTempDirectory("ingest-fallback-");
+        try {
+            Path inputDir = tmpDir.resolve("Input");
+            Path libDir = tmpDir.resolve("Library");
+            Path rejDir = tmpDir.resolve("Rejected");
+            Files.createDirectories(inputDir);
+            Files.createDirectories(libDir);
+            Files.createDirectories(rejDir);
+
+            // 非音频内容但扩展名 .m4a → jaudiotagger 与 FFprobe 都无法识别
+            Path src = inputDir.resolve("garbage.m4a");
+            Files.write(src, "definitely not audio".getBytes(StandardCharsets.UTF_8));
+
+            IngestService service = buildServiceWithValidation();
+            AtomicInteger ingested = new AtomicInteger();
+            AtomicInteger duplicates = new AtomicInteger();
+            AtomicInteger missingMeta = new AtomicInteger();
+            AtomicInteger unreadable = new AtomicInteger();
+            AtomicInteger convFailed = new AtomicInteger();
+            AtomicInteger otherRejected = new AtomicInteger();
+
+            String result = invokeProcessSingleFile(service, src, libDir, rejDir,
+                    new HashSet<>(), new HashSet<>(),
+                    ingested, duplicates, missingMeta, unreadable,
+                    convFailed, otherRejected);
+
+            assertEquals("rejected:unreadable", result,
+                    "FFprobe 也无法识别时应归类 Unreadable");
+            assertEquals(1, unreadable.get());
+            assertTrue(Files.exists(rejDir.resolve("Unreadable").resolve("garbage.m4a")));
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void fallbackPath_stillRunsDuplicateDetection() throws Exception {
+        assumeFfmpeg();
+        Path tmpDir = Files.createTempDirectory("ingest-fallback-");
+        try {
+            Path inputDir = tmpDir.resolve("Input");
+            Path libDir = tmpDir.resolve("Library");
+            Path rejDir = tmpDir.resolve("Rejected");
+            Files.createDirectories(inputDir);
+            Files.createDirectories(libDir);
+            Files.createDirectories(rejDir);
+
+            Path src1 = createMp4ContainerAsAac(inputDir, "dup1.aac",
+                    "Dup Title", "Dup Artist", "Dup Album");
+            Path src2 = createMp4ContainerAsAac(inputDir, "dup2.aac",
+                    "Dup Title", "Dup Artist", "Dup Album");
+
+            IngestService service = buildServiceWithValidation();
+            Set<Object> libraryIds = new HashSet<>();
+            Set<Object> batchIds = new HashSet<>();
+
+            String r1 = invokeProcessSingleFile(service, src1, libDir, rejDir,
+                    libraryIds, batchIds,
+                    new AtomicInteger(), new AtomicInteger(),
+                    new AtomicInteger(), new AtomicInteger(),
+                    new AtomicInteger(), new AtomicInteger());
+            assertEquals("ingested", r1, "首个后备文件应入库");
+
+            AtomicInteger unreadable2 = new AtomicInteger();
+            AtomicInteger duplicates2 = new AtomicInteger();
+            String r2 = invokeProcessSingleFile(service, src2, libDir, rejDir,
+                    libraryIds, batchIds,
+                    new AtomicInteger(), duplicates2,
+                    new AtomicInteger(), unreadable2,
+                    new AtomicInteger(), new AtomicInteger());
+            assertEquals("rejected:duplicate", r2,
+                    "后备路径应继续执行去重检测");
+            assertEquals(1, duplicates2.get());
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void fallbackPath_stillRunsDecodeValidation() throws Exception {
+        assumeFfmpeg();
+        Path tmpDir = Files.createTempDirectory("ingest-fallback-");
+        try {
+            Path inputDir = tmpDir.resolve("Input");
+            Path libDir = tmpDir.resolve("Library");
+            Path rejDir = tmpDir.resolve("Rejected");
+            Files.createDirectories(inputDir);
+            Files.createDirectories(libDir);
+            Files.createDirectories(rejDir);
+
+            // 合法 M4A（jaudiotagger 无法读，FFprobe 元数据齐全）→ 后备路径应被触发
+            Path src = createMp4ContainerAsAac(inputDir, "legit.aac",
+                    "Dec Title", "Dec Artist", "Dec Album");
+            assertJaudiotaggerCannotRead(src);
+
+            // 用受控的 AudioValidationService 替身：
+            //  - readMetadata 走真实实现，确保后备元数据“确实可用”（前置成立）
+            //  - validate() 强制失败，隔离出“完整解码校验”这一步作为唯一失败点
+            AudioValidationService realAvs = new AudioValidationService();
+            AudioValidationService avs = spy(realAvs);
+            doReturn(AudioValidationService.ValidationResult.invalid("模拟解码失败"))
+                    .when(avs).validate(any(Path.class));
+
+            // 前置断言：后备元数据确实可用且完整
+            AudioValidationService.ProbeMetadata pre = avs.readMetadata(src);
+            assertTrue(pre.isAvailable(), "前置条件：FFprobe 后备元数据应可用");
+            assertEquals("Dec Title", pre.getFirst("title"));
+            assertEquals("Dec Artist", pre.getFirst("artist"));
+            assertEquals("Dec Album", pre.getFirst("album"));
+
+            IngestService service = new IngestService(
+                    mock(SimpMessagingTemplate.class),
+                    new ProgressStore(),
+                    new TraditionalFilterService(),
+                    mock(ConfigService.class),
+                    avs);
+
+            AtomicInteger ingested = new AtomicInteger();
+            AtomicInteger unreadable = new AtomicInteger();
+            String result = invokeProcessSingleFile(service, src, libDir, rejDir,
+                    new HashSet<>(), new HashSet<>(),
+                    ingested, new AtomicInteger(),
+                    new AtomicInteger(), unreadable,
+                    new AtomicInteger(), new AtomicInteger());
+
+            assertEquals("rejected:unreadable", result,
+                    "后备/remux 成功但完整解码校验失败时应归类 Unreadable");
+            assertEquals(1, unreadable.get());
+            assertEquals(0, ingested.get());
+            assertTrue(Files.exists(rejDir.resolve("Unreadable").resolve("legit.aac")),
+                    "解码校验失败的源文件应进入 Rejected/Unreadable");
+            // 派生的临时 remux 产物应被清理
+            assertTrue(Files.list(inputDir).noneMatch(p ->
+                    p.getFileName().toString().endsWith(".fallback.m4a")),
+                    "解码校验失败后派生的 remux 产物应被清理");
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void fallbackRemux_producesAudioOnlyOutputDroppingVideo() throws Exception {
+        assumeFfmpeg();
+        Path tmpDir = Files.createTempDirectory("ingest-remux-map-");
+        try {
+            Path inputDir = tmpDir.resolve("Input");
+            Path libDir = tmpDir.resolve("Library");
+            Path rejDir = tmpDir.resolve("Rejected");
+            Files.createDirectories(inputDir);
+            Files.createDirectories(libDir);
+            Files.createDirectories(rejDir);
+
+            // 构造包含真实视频流 + 音频流的 .aac（MP4 容器）文件
+            Path src = createMp4WithVideoAndAudio(inputDir, "withvideo.aac",
+                    "Map Title", "Map Artist", "Map Album");
+            assertJaudiotaggerCannotRead(src);
+            // 前置：源文件确有视频流
+            assertTrue(streamCodecTypes(src).contains("video"),
+                    "前置条件：源文件应包含视频流");
+
+            IngestService service = buildServiceWithValidation();
+            AtomicInteger ingested = new AtomicInteger();
+            String result = invokeProcessSingleFile(service, src, libDir, rejDir,
+                    new HashSet<>(), new HashSet<>(),
+                    ingested, new AtomicInteger(),
+                    new AtomicInteger(), new AtomicInteger(),
+                    new AtomicInteger(), new AtomicInteger());
+
+            assertEquals("ingested", result, "含视频流的合法音频应经后备 remux 入库");
+            Path out = libDir.resolve("Map Artist").resolve("Map Album")
+                    .resolve("01 - Map Title.m4a");
+            assertTrue(Files.exists(out), "应生成入库的 M4A: " + out);
+
+            java.util.List<String> outTypes = streamCodecTypes(out);
+            assertTrue(outTypes.contains("audio"), "输出应保留音频流");
+            assertFalse(outTypes.contains("video"),
+                    "输出不应携带普通视频流（应为干净的音乐资产），实际: " + outTypes);
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void buildRemuxCommand_mapsOnlyFirstAudioStream() throws Exception {
+        IngestService service = buildServiceWithValidation();
+        Method m = IngestService.class.getDeclaredMethod("buildRemuxCommand",
+                Path.class, Path.class, String.class, String.class, String.class, String.class);
+        m.setAccessible(true);
+
+        @SuppressWarnings("unchecked")
+        java.util.List<String> cmd = (java.util.List<String>) m.invoke(service,
+                Paths.get("/tmp/in.aac"), Paths.get("/tmp/out.m4a"),
+                "T", "A", "Al", "AA");
+
+        // 必须显式仅映射第一个音频流，且不得使用无限制的 -map 0
+        int mapIdx = cmd.indexOf("-map");
+        assertTrue(mapIdx >= 0, "应包含 -map 参数");
+        assertEquals("0:a:0", cmd.get(mapIdx + 1), "应仅映射第一个音频流");
+        // 确认没有任何 '-map 0' 无限制映射
+        for (int i = 0; i < cmd.size() - 1; i++) {
+            if ("-map".equals(cmd.get(i))) {
+                assertNotEquals("0", cmd.get(i + 1),
+                        "不得使用无限制的 -map 0（会带入视频/字幕/数据流）");
+            }
+        }
+        assertTrue(cmd.contains("copy"), "应无损复制音频（-c copy）");
+    }
+
+    @Test
+    void runFfmpegDrained_doesNotDeadlockOnVerboseOutput() throws Exception {
+        // 使用产生大量输出的可控进程验证并发排空不会因管道写满而死锁。
+        // 该测试不依赖 ffmpeg，直接反射调用 runFfmpegDrained。
+        Path tmpDir = Files.createTempDirectory("ffmpeg-drain-");
+        try {
+            IngestService service = buildService();
+            Method m = IngestService.class.getDeclaredMethod("runFfmpegDrained",
+                    java.util.List.class, int.class, Path.class, String.class);
+            m.setAccessible(true);
+
+            // 产生远超管道缓冲区（通常 64KB）的输出：约 2MB
+            java.util.List<String> cmd = Arrays.asList(
+                    "sh", "-c",
+                    "i=0; while [ $i -lt 40000 ]; do " +
+                    "echo 'noisy ffmpeg style diagnostic line to fill the pipe buffer'; " +
+                    "i=$((i+1)); done");
+
+            long start = System.currentTimeMillis();
+            // 成功退出（exit 0）→ 不抛异常；若死锁则会一直阻塞直到超时
+            m.invoke(service, cmd, 30, null, "test");
+            long elapsed = System.currentTimeMillis() - start;
+
+            assertTrue(elapsed < 25_000,
+                    "并发排空应快速完成而非因管道写满死锁，耗时(ms)=" + elapsed);
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
+    @Test
+    void runFfmpegDrained_nonZeroExitCleansOutputAndThrows() throws Exception {
+        Path tmpDir = Files.createTempDirectory("ffmpeg-drain-fail-");
+        try {
+            IngestService service = buildService();
+            Method m = IngestService.class.getDeclaredMethod("runFfmpegDrained",
+                    java.util.List.class, int.class, Path.class, String.class);
+            m.setAccessible(true);
+
+            Path output = tmpDir.resolve("out.m4a");
+            Files.write(output, "partial".getBytes(StandardCharsets.UTF_8));
+
+            // 命令先产生大量输出再以非零退出，验证：不死锁、清理输出、抛异常
+            java.util.List<String> cmd = Arrays.asList(
+                    "sh", "-c",
+                    "i=0; while [ $i -lt 20000 ]; do echo 'noise line'; i=$((i+1)); done; exit 3");
+
+            try {
+                m.invoke(service, cmd, 30, output, "test");
+                fail("非零退出应抛出异常");
+            } catch (java.lang.reflect.InvocationTargetException e) {
+                assertTrue(e.getCause() instanceof RuntimeException,
+                        "应抛出 RuntimeException，实际: " + e.getCause());
+                assertTrue(e.getCause().getMessage().contains("退出码"),
+                        "异常应包含退出码信息");
+            }
+            assertFalse(Files.exists(output), "失败时应清理输出文件");
+        } finally {
+            deleteDirectory(tmpDir);
+        }
+    }
+
     // ========== 工具方法 ==========
 
+    /**
+     * 创建一个 MP4/M4A 容器但使用 .aac 扩展名的文件。
+     * <p>jaudiotagger 按扩展名分派 reader，会因缺少 AAC reader 而拒绝；
+     * FFprobe 通过内容探测能识别并读取完整元数据。用于触发后备读取路径。</p>
+     */
+    private static Path createMp4ContainerAsAac(Path dir, String name,
+                                                String title, String artist, String album) throws Exception {
+        Path file = dir.resolve(name);
+        java.util.List<String> cmd = new java.util.ArrayList<>(Arrays.asList(
+                "ffmpeg", "-y", "-f", "lavfi", "-i", "anullsrc=r=44100:cl=mono",
+                "-t", "0.3", "-c:a", "aac", "-f", "mp4"));
+        if (title != null) { cmd.add("-metadata"); cmd.add("title=" + title); }
+        if (artist != null) { cmd.add("-metadata"); cmd.add("artist=" + artist); }
+        if (album != null) { cmd.add("-metadata"); cmd.add("album=" + album); }
+        cmd.add(file.toAbsolutePath().toString());
+        runProcessChecked(new ProcessBuilder(cmd), "ffmpeg");
+        return file;
+    }
+
+    /**
+     * 创建一个同时包含真实视频流与音频流的 MP4/M4A 容器（.aac 扩展名）。
+     * 用于验证后备 remux 仅保留音频、丢弃普通视频流。
+     */
+    private static Path createMp4WithVideoAndAudio(Path dir, String name,
+                                                   String title, String artist, String album) throws Exception {
+        Path file = dir.resolve(name);
+        java.util.List<String> cmd = new java.util.ArrayList<>(Arrays.asList(
+                "ffmpeg", "-y",
+                "-f", "lavfi", "-i", "anullsrc=r=44100:cl=mono",
+                "-f", "lavfi", "-i", "testsrc=s=64x64:d=0.3",
+                "-map", "0:a", "-map", "1:v",
+                "-c:a", "aac", "-c:v", "libx264",
+                "-shortest", "-t", "0.3", "-f", "mp4"));
+        if (title != null) { cmd.add("-metadata"); cmd.add("title=" + title); }
+        if (artist != null) { cmd.add("-metadata"); cmd.add("artist=" + artist); }
+        if (album != null) { cmd.add("-metadata"); cmd.add("album=" + album); }
+        cmd.add(file.toAbsolutePath().toString());
+        runProcessChecked(new ProcessBuilder(cmd), "ffmpeg");
+        return file;
+    }
+
+    /**
+     * 用 ffprobe 返回文件中所有流的 codec_type 列表。
+     */
+    private static java.util.List<String> streamCodecTypes(Path file) throws Exception {
+        ProcessBuilder pb = new ProcessBuilder(
+                "ffprobe", "-v", "error",
+                "-show_entries", "stream=codec_type",
+                "-of", "default=nw=1:nk=1",
+                file.toAbsolutePath().toString());
+        pb.redirectErrorStream(true);
+        Process p = pb.start();
+        String out = readStream(p.getInputStream());
+        p.waitFor(10, TimeUnit.SECONDS);
+        java.util.List<String> types = new java.util.ArrayList<>();
+        for (String line : out.split("\\R")) {
+            String t = line.trim();
+            if (!t.isEmpty()) types.add(t);
+        }
+        return types;
+    }
+
+    /**
+     * 断言 jaudiotagger 无法读取该文件（无 tag 或抛异常），确认后备路径确会被触发。
+     */
+    private static void assertJaudiotaggerCannotRead(Path file) {
+        boolean readable;
+        try {
+            AudioFile af = AudioFileIO.read(file.toFile());
+            readable = af.getTag() != null;
+        } catch (Exception e) {
+            readable = false;
+        }
+        assertFalse(readable, "前置条件：jaudiotagger 应无法读取该文件的标签");
+    }
+
     private IngestService buildService() {
         return new IngestService(
                 mock(SimpMessagingTemplate.class),