使用 mp4parser 剪辑 mp4。无法通过时间使用 SyncSample 进行更正

Question

我正在编写一个 Android 应用程序，我有一堆 5-15 秒的 .mp4 文件要剪辑。我一直在尝试使用 Sebastian Annies 的 mp4parser来执行此操作，遵循此处给出的示例代码：ShortenExample。

这是我正在使用的代码（与上面的示例代码非常相似）：

    public static void clip(Sprinkle sprinkle, double start, double end) throws IOException {
    Movie movie = MovieCreator.build(sprinkle.getLocalVideoPath());

    // Save all tracks then remove them from movie
    List<Track> tracks = movie.getTracks();
    movie.setTracks(new LinkedList<Track>());

    boolean timeCorrected = false;

    // Here we try to find a track that has sync samples. Since we can only start decoding
    // at such a sample we SHOULD make sure that the start of the new fragment is exactly
    // such a frame
    for (Track track : tracks) {
        if (track.getSyncSamples() != null && track.getSyncSamples().length > 0) {
            if (timeCorrected) {
                // This exception here could be a false positive in case we have multiple tracks
                // with sync samples at exactly the same positions. E.g. a single movie containing
                // multiple qualities of the same video (Microsoft Smooth Streaming file)
                Log.v("clip", "track.getSyncSamples().length: " + track.getSyncSamples().length);
                throw new RuntimeException("The startTime has already been corrected by another track with SyncSample. Not Supported.");
            }
            Log.v("syncSample", "start before: " + start);
            Log.v("syncSample", "end before: " + end);
            start = correctTimeToSyncSample(track, start, false);
            end = correctTimeToSyncSample(track, end, true);
            Log.v("syncSample", "start after: " + start);
            Log.v("syncSample", "end after: " + end);
            timeCorrected = true;
        }
    }

    for (Track track : tracks) {
        long currentSample = 0;
        double currentTime = 0;
        double lastTime = 0;
        long startSample = -1;
        long endSample = -1;

        for (int i = 0; i < track.getDecodingTimeEntries().size(); i++) {
            TimeToSampleBox.Entry entry = track.getDecodingTimeEntries().get(i);
            for (int j = 0; j < entry.getCount(); j++) {
                if (currentTime > lastTime && currentTime <= start) {
                    // current sample is still before the new starttime
                    startSample = currentSample;
                }
                if (currentTime > lastTime && currentTime <= end) {
                    // current sample is after the new start time and still before the new endtime
                    endSample = currentSample;
                }
                lastTime = currentTime;
                currentTime += (double) entry.getDelta() / (double) track.getTrackMetaData().getTimescale();
                currentSample++;
            }
        }
        movie.addTrack(new AppendTrack(new CroppedTrack(track, startSample, endSample)));
    }

    long start1 = System.currentTimeMillis();
    Container out = new DefaultMp4Builder().build(movie);
    long start2 = System.currentTimeMillis();
    File file = Constants.getEditsDir();
    FileOutputStream fos = new FileOutputStream(file.getPath() + String.format("output-%f-%f.mp4", start, end));
    FileChannel fc = fos.getChannel();
    out.writeContainer(fc);
    fc.close();
    fos.close();
    long start3 = System.currentTimeMillis();
    System.err.println("Building IsoFile took : " + (start2 - start1) + "ms");
    System.err.println("Writing IsoFile took  : " + (start3 - start2) + "ms");
    System.err.println("Writing IsoFile speed : " + (new File(String.format("output-%f-%f.mp4", start, end)).length() / (start3 - start2) / 1000) + "MB/s");

}

private static double correctTimeToSyncSample(Track track, double cutHere, boolean next) {
    double[] timeOfSyncSamples = new double[track.getSyncSamples().length];
    long currentSample = 0;
    double currentTime = 0;
    for (int i = 0; i < track.getDecodingTimeEntries().size(); i++) {
        TimeToSampleBox.Entry entry = track.getDecodingTimeEntries().get(i);
        for (int j = 0; j < entry.getCount(); j++) {
            if (Arrays.binarySearch(track.getSyncSamples(), currentSample + 1) >= 0) {
                // samples always start with 1 but we start with zero therefore +1
                timeOfSyncSamples[Arrays.binarySearch(track.getSyncSamples(), currentSample + 1)] = currentTime;
            }
            currentTime += (double) entry.getDelta() / (double) track.getTrackMetaData().getTimescale();
            currentSample++;
        }
    }
    double previous = 0;
    for (double timeOfSyncSample : timeOfSyncSamples) {
        if (timeOfSyncSample > cutHere) {
            if (next) {
                return timeOfSyncSample;
            } else {
                return previous;
            }
        }
        previous = timeOfSyncSample;
    }
    return timeOfSyncSamples[timeOfSyncSamples.length - 1];
}

我似乎无法阻止错误“startTime 已经被 SyncSample 的另一个轨道纠正。不支持。” 从发生。当我记录我正在循环的曲目时，getHandler() 返回“视频”、“声音”，然后在涉及“提示”时崩溃。如果我注释掉这部分：

    if (timeCorrected) {
            // This exception here could be a false positive in case we have multiple tracks
            // with sync samples at exactly the same positions. E.g. a single movie containing
            // multiple qualities of the same video (Microsoft Smooth Streaming file)
            Log.v("clip", "track.getSyncSamples().length: " + track.getSyncSamples().length);
            throw new RuntimeException("The startTime has already been corrected by another track with SyncSample. Not Supported.");
        }

然后程序在到达该行时因索引越界错误而崩溃

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

我究竟做错了什么？

Answer 1

您收到 IndexOutOfBoundsException，因为您的startSample或您的endSample在到达时有错误的值（例如仍然是-1）

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

在我的示例中，使用start小于 2 秒的剪辑过程值会导致效果if (currentTime > lastTime && currentTime <= start)从未达到真实值，因此startSample不会从其初始值 -1 进行更新。一种解决方案是将初始值startSample从 -1 更改为 0。