如何连接/合并mp4，设置正确的持续时间？

Question

我需要在android上合并几个mp4文件，所以我尝试使用mp4parser合并几个mp4。

private void mergeMp4(File output, String[] files) throws IOException {
    Movie[] inMovies = new Movie[files.length];
    for (int i=0, len = files.length; i<len; ++i) {
        inMovies[i] = MovieCreator.build("/tmp/tmp/" + files[i]);
    }

    List<Track> videoTracks = new LinkedList<Track>();
    List<Track> audioTracks = new LinkedList<Track>();

    for (Movie m : inMovies) {
        for (Track t : m.getTracks()) {
            if (t.getHandler().equals("soun")) {
                audioTracks.add(t);
            }
            if (t.getHandler().equals("vide")) {
                videoTracks.add(t);
            }
        }
    }

    Movie result = new Movie();
    if (audioTracks.size() > 0) {
        result.addTrack(new AppendTrack(audioTracks.toArray(new Track[audioTracks.size()])));
    }
    if (videoTracks.size() > 0) {
        result.addTrack(new AppendTrack(videoTracks.toArray(new Track[videoTracks.size()])));
    }

    Container out = new DefaultMp4Builder().build(result);

    FileChannel fc = new RandomAccessFile(output, "rw").getChannel();
    out.writeContainer(fc);
    fc.close();
}

// work correct for non-merged mp4 file
private long getDuration(String filename) throws IOException {
    IsoFile isoFile = new IsoFile(filename);
    long lengthInSeconds = isoFile.getMovieBox().getMovieHeaderBox().getDuration() / isoFile.getMovieBox().getMovieHeaderBox().getTimescale();

    return lengthInSeconds * 1000;
} 

代码中的某处

File tmp = new File("/tmp/tmp");
String[] tmpFiles = tmp.list();
File recordedFile = new File("/mnt/sdcard/app/output.mp4")
mergeMp4(recordedFile, tmpFiles);
// both print value near 0 (about 20 millis)
Log.d("TAG", String.valueOf(getDuration(recordedFile)));
System.out.println(getDuration(recordedFile));

如果我尝试使用Android MediaPlayer或任何其他播放器播放合并文件：

player = new MediaPlayer();
try {
    player.setDataSource(getFilename());
    player.prepare();
    player.start();
    int duration = player.getDuaration();
    // both print value near 0 (about 20 millis)
    Log.d("TAG", String.valueOf(duration));
    System.out.println(duration);
} catch (IOException e) {
    Log.e(TAG, "prepare() failed", e);
}

它是合并文件，但所有媒体播放器甚至mp4parser获取持续时间的作者的方法都返回该持续时间总是大约0（零）秒。