我有一系列的mp4文件保存在设备上，需要合并在一起，使一个单一的mp4文件。
视频\u p1.mp4视频\u p2.mp4视频\u p3.mp4>视频.mp4
我研究过的解决方案，比如mp4parser框架，都使用了不推荐使用的代码。
我能找到的最好的解决方案是使用mediamuxer和mediaextractor。
代码运行，但我的视频不会被合并（只显示video_p1.mp4中的内容，它是横向的，而不是纵向的）。
有人能帮我解决这个问题吗？

public static boolean concatenateFiles(File dst, File... sources) {
    if ((sources == null) || (sources.length == 0)) {
        return false;
    }

    boolean result;
    MediaExtractor extractor = null;
    MediaMuxer muxer = null;
    try {
        // Set up MediaMuxer for the destination.
        muxer = new MediaMuxer(dst.getPath(), MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);

        // Copy the samples from MediaExtractor to MediaMuxer.
        boolean sawEOS = false;
        //int bufferSize = MAX_SAMPLE_SIZE;
        int bufferSize = 1 * 1024 * 1024;
        int frameCount = 0;
        int offset = 100;

        ByteBuffer dstBuf = ByteBuffer.allocate(bufferSize);
        MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();

        long timeOffsetUs = 0;
        int dstTrackIndex = -1;

        for (int fileIndex = 0; fileIndex < sources.length; fileIndex++) {
            int numberOfSamplesInSource = getNumberOfSamples(sources[fileIndex]);

            // Set up MediaExtractor to read from the source.
            extractor = new MediaExtractor();
            extractor.setDataSource(sources[fileIndex].getPath());

            // Set up the tracks.
            SparseIntArray indexMap = new SparseIntArray(extractor.getTrackCount());
            for (int i = 0; i < extractor.getTrackCount(); i++) {
                extractor.selectTrack(i);
                MediaFormat format = extractor.getTrackFormat(i);
                if (dstTrackIndex < 0) {
                    dstTrackIndex = muxer.addTrack(format);
                    muxer.start();
                }
                indexMap.put(i, dstTrackIndex);
            }

            long lastPresentationTimeUs = 0;
            int currentSample = 0;

            while (!sawEOS) {
                bufferInfo.offset = offset;
                bufferInfo.size = extractor.readSampleData(dstBuf, offset);

                if (bufferInfo.size < 0) {
                    sawEOS = true;
                    bufferInfo.size = 0;
                    timeOffsetUs += (lastPresentationTimeUs + 0);
                }
                else {
                    lastPresentationTimeUs = extractor.getSampleTime();
                    bufferInfo.presentationTimeUs = extractor.getSampleTime() + timeOffsetUs;
                    bufferInfo.flags = extractor.getSampleFlags();
                    int trackIndex = extractor.getSampleTrackIndex();

                    if ((currentSample < numberOfSamplesInSource) || (fileIndex == sources.length - 1)) {
                        muxer.writeSampleData(indexMap.get(trackIndex), dstBuf, bufferInfo);
                    }
                    extractor.advance();

                    frameCount++;
                    currentSample++;
                    Log.d("tag2", "Frame (" + frameCount + ") " +
                                "PresentationTimeUs:" + bufferInfo.presentationTimeUs +
                                " Flags:" + bufferInfo.flags +
                                " TrackIndex:" + trackIndex +
                                " Size(KB) " + bufferInfo.size / 1024);

                }
            }
            extractor.release();
            extractor = null;
        }

        result = true;
    }
    catch (IOException e) {
        result = false;
    }
    finally {
        if (extractor != null) {
            extractor.release();
        }
        if (muxer != null) {
            muxer.stop();
            muxer.release();
        }
    }
    return result;
}

public static int getNumberOfSamples(File src) {
    MediaExtractor extractor = new MediaExtractor();
    int result;
    try {
        extractor.setDataSource(src.getPath());
        extractor.selectTrack(0);

        result = 0;
        while (extractor.advance()) {
            result ++;
        }
    }
    catch(IOException e) {
        result = -1;
    }
    finally {
        extractor.release();
    }
    return result;
}