mediamuxer视频截取

您可以使用 MediaMuxer 类来截取视频。以下是一个示例代码：

public void extractVideo(String inputPath, String outputPath, int startMs, int endMs) throws IOException {
    // Set up MediaExtractor to read from the source.
    MediaExtractor extractor = new MediaExtractor();
    extractor.setDataSource(inputPath);

    // Set up MediaMuxer for the destination.
    MediaMuxer muxer = new MediaMuxer(outputPath, MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);

    // Set up the video track.
    int videoTrackIndex = -1;
    for (int i = 0; i < extractor.getTrackCount(); i++) {
        MediaFormat format = extractor.getTrackFormat(i);
        String mime = format.getString(MediaFormat.KEY_MIME);
        if (mime.startsWith("video/")) {
            extractor.selectTrack(i);
            videoTrackIndex = muxer.addTrack(format);
            break;
        }
    }
    if (videoTrackIndex == -1) {
        throw new RuntimeException("No video track found in " + inputPath);
    }

    // Set up the output format.
    MediaFormat outputFormat = MediaFormat.createVideoFormat("video/avc", 1280, 720);
    outputFormat.setInteger(MediaFormat.KEY_COLOR_FORMAT, MediaCodecInfo.CodecCapabilities.COLOR_FormatSurface);
    outputFormat.setInteger(MediaFormat.KEY_BIT_RATE, 2000000);
    outputFormat.setInteger(MediaFormat.KEY_FRAME_RATE, 30);
    outputFormat.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, 10);
    muxer.setOrientationHint(0);
    muxer.start();

    // Extract and write the video frames.
    ByteBuffer inputBuffer = ByteBuffer.allocate(1024 * 1024);
    MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
    boolean sawInputEOS = false;
    long lastPresentationTimeUs = -1;
    extractor.seekTo(startMs * 1000, MediaExtractor.SEEK_TO_CLOSEST_SYNC);
    while (!sawInputEOS) {
        int inputBufferIndex = extractor.getSampleTrackIndex();
        if (inputBufferIndex == videoTrackIndex) {
            int chunkSize = extractor.readSampleData(inputBuffer, 0);
            if (chunkSize < 0) {
                sawInputEOS = true;
                chunkSize = 0;
            }
            long presentationTimeUs = extractor.getSampleTime();
            if (endMs > 0 && presentationTimeUs > endMs * 1000) {
                sawInputEOS = true;
                chunkSize = 0;
            } else {
                extractor.advance();
            }
            if (chunkSize > 0) {
                inputBuffer.position(0);
                inputBuffer.limit(chunkSize);
                if (lastPresentationTimeUs != -1) {
                    bufferInfo.presentationTimeUs = presentationTimeUs - lastPresentationTimeUs;
                } else {
                    bufferInfo.presentationTimeUs = 0;
                }
                lastPresentationTimeUs = presentationTimeUs;
                bufferInfo.flags = extractor.getSampleFlags();
                muxer.writeSampleData(videoTrackIndex, inputBuffer, bufferInfo);
            }
        } else if (inputBufferIndex == -1) {
            sawInputEOS = true;
        } else {
            extractor.advance();
        }
    }

    // Release everything.
    extractor.release();
    muxer.stop();
    muxer.release();
}

这个方法将从 `inputPath` 指定的路径读取视频文件，并提取第一个视频轨道。然后，它将写入一个新的视频文件，从 `startMs` 开始，到 `endMs` 结束。如果 `endMs` 为 0，则会一直写入到文件的结尾。最后，它释放了所有资源。

请注意，这只是一个示例代码，您需要根据您自己的需求进行修改。其中一些参数，如输出格式、视频大小、比特率、帧速率等，应根据您的需要进行更改。