多媒体系统之MediaMuxer和MediaExtractor（五）

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MediaExtractor主要用于提取音视频相关信息，分离音视频。
MediaMuxer主要复用和解复用音视频。

MediaExtractor使用一般步骤

1.//设置数据源
setDataSource
2.//分离轨道
getTrackCount，getTrackFormat
3.//选择轨道
selectTrack，unselectTrack
4.//读取数据
readSampleData
5.//下一帧
advance
6.//释放
release

举例说明：

int trackCount = mediaExtractor.getTrackCount();
for (int i = 0; i < trackCount; i++) {MediaFormat trackFormat = mediaExtractor.getTrackFormat(i);String mime = trackFormat.getString(MediaFormat.KEY_MIME);if (mime.startsWith("video/")) {mediaExtractor.selectTrack(i);break;} else if (mime.startsWith("audio/")) {mediaExtractor.selectTrack(i);break;}}

MediaMuxer使用一般步骤

1.//添加轨道
addTrack
2.写数据
writeSampleData
3.释放
release

注意点

 buffinfo 必须设置相应的有效值，不然会引发错误//写入数据大小bufferInfo.size = readSampleDataSize;//偏移量bufferInfo.offset = 0;//是否为关键帧bufferInfo.flags = mediaExtractor.getSampleFlags();//PTS 单位为微妙，必须为递增不然会报错bufferInfo.presentationTimeUs += videoSampleTime;mediaMuxer.writeSampleData(trackIndex, buffer, bufferInfo);这里重点关注下
bufferInfo.presentationTimeUs
mediaExtractor.getSampleTime()
因为mediaExtractor的提取顺序应该是dts的顺序不是pts的顺序，如果视频中存在b帧则getSampleTime不可能递增的，所以bufferInfo.presentationTimeUs=mediaExtractor.getSampleTime()可能会报错，前面说了这个值必须递增。如果不存在b帧，pts==dts，使用没问题。

设置PTS的办法
1.算出帧时间距,github上看见的，排除i帧来计算不知道是为什么，不排除感觉也一样的

        long videoSampleTime;
//            mediaExtractor.readSampleData(buffer, 0);
//            //skip first I frame
//            if (mediaExtractor.getSampleFlags() == MediaExtractor.SAMPLE_FLAG_SYNC)
//                mediaExtractor.advance();mediaExtractor.readSampleData(buffer, 0);long firstVideoPTS = mediaExtractor.getSampleTime();mediaExtractor.advance();mediaExtractor.readSampleData(buffer, 0);long SecondVideoPTS = mediaExtractor.getSampleTime();videoSampleTime = Math.abs(SecondVideoPTS - firstVideoPTS);

2.通过帧率来计算

//每秒多少帧
int frameRate=mediaFormat=getInteger(MediaFormat.KEY_FRAME_RATE)
//得出平均每一帧间隔多少微妙
videoSampleTime=1000*1000/frameRate

最后提供2个简单的运用示例
有耗时，不要ui线程使用，只是演示

    /*** 提取音/视频** @param inPath* @param outPath* @param isVideo*/@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)public static void trackExtractor(String inPath, String outPath, boolean isVideo) {//提取器MediaExtractor mediaExtractor = new MediaExtractor();try {mediaExtractor.setDataSource(inPath);} catch (IOException e) {e.printStackTrace();}MediaMuxer mediaMuxer = null;//复用器try {mediaMuxer = new MediaMuxer(outPath, MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);} catch (IOException e) {e.printStackTrace();}int trackIndex = 0;int trackCount = mediaExtractor.getTrackCount();for (int i = 0; i < trackCount; i++) {MediaFormat trackFormat = mediaExtractor.getTrackFormat(i);String mime = trackFormat.getString(MediaFormat.KEY_MIME);if (mime.startsWith("video/") && isVideo) {trackIndex = mediaMuxer.addTrack(trackFormat);mediaExtractor.selectTrack(i);break;} else if (mime.startsWith("audio/") && !isVideo) {trackIndex = mediaMuxer.addTrack(trackFormat);mediaExtractor.selectTrack(i);break;}}mediaMuxer.start();ByteBuffer buffer = ByteBuffer.allocate(1024 * 1000);MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();long videoSampleTime=getSampleTime(mediaExtractor,buffer);while (true) {int readSampleDataSize = mediaExtractor.readSampleData(buffer, 0);if (readSampleDataSize < 0) {break;}bufferInfo.size = readSampleDataSize;bufferInfo.offset = 0;bufferInfo.flags = mediaExtractor.getSampleFlags();bufferInfo.presentationTimeUs += videoSampleTime;mediaMuxer.writeSampleData(trackIndex, buffer, bufferInfo);mediaExtractor.advance();}mediaExtractor.release();mediaMuxer.stop();//内部也会执行stop，所以可以不用执行stopmediaMuxer.release();}private static long getSampleTime(MediaExtractor mediaExtractor, ByteBuffer buffer) {long videoSampleTime;
//            mediaExtractor.readSampleData(buffer, 0);
//            //skip first I frame
//            if (mediaExtractor.getSampleFlags() == MediaExtractor.SAMPLE_FLAG_SYNC)
//                mediaExtractor.advance();mediaExtractor.readSampleData(buffer, 0);long firstVideoPTS = mediaExtractor.getSampleTime();mediaExtractor.advance();mediaExtractor.readSampleData(buffer, 0);long SecondVideoPTS = mediaExtractor.getSampleTime();videoSampleTime = Math.abs(SecondVideoPTS - firstVideoPTS);Log.d("MediaMuxerUtil", "videoSampleTime is " + videoSampleTime);return videoSampleTime;}/*** 合成音视频** @param videoPath* @param audioPath* @param outPath*/@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)public static void trackMuxer(String videoPath, String audioPath, String outPath) {MediaExtractor videoExtractor = new MediaExtractor();try {videoExtractor.setDataSource(videoPath);} catch (IOException e) {e.printStackTrace();}MediaFormat videoFormat = null;int videoTrackIndex = -1;int videoTrackCount = videoExtractor.getTrackCount();for (int i = 0; i < videoTrackCount; i++) {videoFormat = videoExtractor.getTrackFormat(i);String mime = videoFormat.getString(MediaFormat.KEY_MIME);if (mime.startsWith("video/")) {videoTrackIndex = i;break;}}MediaExtractor audioExtractor = new MediaExtractor();try {audioExtractor.setDataSource(audioPath);} catch (IOException e) {e.printStackTrace();}MediaFormat audioFormat = null;int audioTrackIndex = -1;int audioTrackCount = audioExtractor.getTrackCount();for (int i = 0; i < audioTrackCount; i++) {audioFormat = audioExtractor.getTrackFormat(i);String mime = audioFormat.getString(MediaFormat.KEY_MIME);if (mime.startsWith("audio/")) {audioTrackIndex = i;break;}}videoExtractor.selectTrack(videoTrackIndex);audioExtractor.selectTrack(audioTrackIndex);MediaCodec.BufferInfo videoBufferInfo = new MediaCodec.BufferInfo();MediaCodec.BufferInfo audioBufferInfo = new MediaCodec.BufferInfo();MediaMuxer mediaMuxer = null;try {mediaMuxer = new MediaMuxer(outPath, MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);} catch (IOException e) {e.printStackTrace();}int writeVideoTrackIndex = mediaMuxer.addTrack(videoFormat);int writeAudioTrackIndex = mediaMuxer.addTrack(audioFormat);mediaMuxer.start();ByteBuffer byteBuffer = ByteBuffer.allocate(1024 * 1000);long videoSampleTime=getSampleTime(videoExtractor,byteBuffer);while (true) {int readVideoSampleSize = videoExtractor.readSampleData(byteBuffer, 0);if (readVideoSampleSize < 0) {break;}videoBufferInfo.size = readVideoSampleSize;videoBufferInfo.presentationTimeUs +=videoSampleTime;videoBufferInfo.offset = 0;videoBufferInfo.flags = videoExtractor.getSampleFlags();mediaMuxer.writeSampleData(writeVideoTrackIndex, byteBuffer, videoBufferInfo);videoExtractor.advance();}long audioSampleTime=getSampleTime(audioExtractor,byteBuffer);while (true) {int readAudioSampleSize = audioExtractor.readSampleData(byteBuffer, 0);if (readAudioSampleSize < 0) {break;}audioBufferInfo.size = readAudioSampleSize;audioBufferInfo.presentationTimeUs += audioSampleTime;audioBufferInfo.offset = 0;audioBufferInfo.flags = audioExtractor.getSampleFlags();mediaMuxer.writeSampleData(writeAudioTrackIndex, byteBuffer, audioBufferInfo);audioExtractor.advance();}mediaMuxer.stop();mediaMuxer.release();videoExtractor.release();audioExtractor.release();}

原文链接：https://blog.csdn.net/u012098794/article/details/55511623
阿里P7移动互联网架构师进阶视频（每日更新中）免费学习请点击：https://space.bilibili.com/474380680

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多媒体系统之MediaMuxer和MediaExtractor（五）

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