Android提供了一个MediaExtractor类，可以用来分离容器中的视频track和音频track，下面的例子展示了使用MediaExtractor和MediaMuxer来实现视频的换音：
private void muxingAudioAndVideo() throws IOException { MediaMuxer mMediaMuxer = new MediaMuxer(mOutputVideoPath, MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4); // 视频的MediaExtractor MediaExtractor mVideoExtractor = new MediaExtractor(); mVideoExtractor.setDataSource(mVideoPath); int videoTrackIndex = -1; for (int i = 0; i < mVideoExtractor.getTrackCount(); i++) { MediaFormat format = mVideoExtractor.getTrackFormat(i); if (format.getString(MediaFormat.KEY_MIME).startsWith("video/")) { mVideoExtractor.selectTrack(i); videoTrackIndex = mMediaMuxer.addTrack(format); break; } } // 音频的MediaExtractor MediaExtractor mAudioExtractor = new MediaExtractor(); mAudioExtractor.setDataSource(mAudioPath); int audioTrackIndex = -1; for (int i = 0; i < mAudioExtractor.getTrackCount(); i++) { MediaFormat format = mAudioExtractor.getTrackFormat(i); if (format.getString(MediaFormat.KEY_MIME).startsWith("audio/")) { mAudioExtractor.selectTrack(i); audioTrackIndex = mMediaMuxer.addTrack(format); } } // 添加完所有轨道后start mMediaMuxer.start(); // 封装视频track if (-1 != videoTrackIndex) { MediaCodec.BufferInfo info = new MediaCodec.BufferInfo(); info.presentationTimeUs = 0; ByteBuffer buffer = ByteBuffer.allocate(100 * 1024); while (true) { int sampleSize = mVideoExtractor.readSampleData(buffer, 0); if (sampleSize < 0) { break; } info.offset = 0; info.size = sampleSize; info.flags = MediaCodec.BUFFER_FLAG_SYNC_FRAME; info.presentationTimeUs = mVideoExtractor.getSampleTime(); mMediaMuxer.writeSampleData(videoTrackIndex, buffer, info); mVideoExtractor.advance(); } } // 封装音频track if (-1 != audioTrackIndex) { MediaCodec.BufferInfo info = new MediaCodec.BufferInfo(); info.presentationTimeUs = 0; ByteBuffer buffer = ByteBuffer.allocate(100 * 1024); while (true) { int sampleSize = mAudioExtractor.readSampleData(buffer, 0); if (sampleSize < 0) { break; } info.offset = 0; info.size = sampleSize; info.flags = MediaCodec.BUFFER_FLAG_SYNC_FRAME; info.presentationTimeUs = mAudioExtractor.getSampleTime(); mMediaMuxer.writeSampleData(audioTrackIndex, buffer, info); mAudioExtractor.advance(); } } // 释放MediaExtractor mVideoExtractor.release(); mAudioExtractor.release(); // 释放MediaMuxer mMediaMuxer.stop(); mMediaMuxer.release(); }