Android媒体解码MediaCodec,MediaExtractor

Android提供了MediaPlayer播放器播放媒体文件，其实MediaPlyer只是对Android Media包下的MediaCodec和MediaExtractor进行了包装，方便使用。但是最好理解下Android媒体文件的解码，编码和渲染流程。

Shape Of My Heart.mp4

<source src="http://7xoquj.com1.z0.glb.clouddn.com/shape_of_my_heart.mp4" type="video/mp4">

使用android.media包下的MediaCodec和MediaExtractor实现一个简单的视频解码渲染。

使用到了:

• MediaCodec:负责媒体文件的编码和解码工作，内部方法均为native
• MediaExtractor:负责将指定类型的媒体文件从文件中找到轨道，并填充到MediaCodec的缓冲区中
• AudioTrack:负责将解码之后的音频播放
• SurfaceView:展示解码之后的视频

视频被播放主要分为以下步骤:

1. 将资源加载到extractor
2. 获取视频所在轨道
3. 设置extractor选中视频所在轨道
4. 创将解码视频的MediaCodec，decoder
5. 开始循环，直到视频资源的末尾
6. 将extractor中资源以一个单位填充进decoder的输入缓冲区
7. decoder将解码之后的视频填充到输出缓冲区
8. decoder释放输出缓冲区的同时，将缓冲区中数据渲染到surface

音频的播放类似，只多了AudioTrack部分，少了渲染到surface部分。

MediaCodec.releaseOutputBuffer(int outputBufferIndex, boolean render);

• render为true就会渲染到surface

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播放的控制，视频和音频各自拥有一个Thread。

    public void play() {isPlaying = true;if (videoThread == null) {videoThread = new VideoThread();videoThread.start();}if (audioThread == null) {audioThread = new AudioThread();audioThread.start();}}public void stop() {isPlaying = false;}

VideoThread

private class VideoThread extends Thread {@Overridepublic void run() {MediaExtractor videoExtractor = new MediaExtractor();MediaCodec videoCodec = null;try {videoExtractor.setDataSource(filePath);} catch (IOException e) {e.printStackTrace();}int videoTrackIndex;//获取视频所在轨道videoTrackIndex = getMediaTrackIndex(videoExtractor, "video/");if (videoTrackIndex >= 0) {MediaFormat mediaFormat = videoExtractor.getTrackFormat(videoTrackIndex);int width = mediaFormat.getInteger(MediaFormat.KEY_WIDTH);int height = mediaFormat.getInteger(MediaFormat.KEY_HEIGHT);//视频长度:秒float time = mediaFormat.getLong(MediaFormat.KEY_DURATION) / 1000000;callBack.videoAspect(width, height, time);videoExtractor.selectTrack(videoTrackIndex);try {videoCodec = MediaCodec.createDecoderByType(mediaFormat.getString(MediaFormat.KEY_MIME));videoCodec.configure(mediaFormat, surface, null, 0);} catch (IOException e) {e.printStackTrace();}}if (videoCodec == null) {Log.v(TAG, "MediaCodec null");return;}videoCodec.start();MediaCodec.BufferInfo videoBufferInfo = new MediaCodec.BufferInfo();ByteBuffer[] inputBuffers = videoCodec.getInputBuffers();
//            ByteBuffer[] outputBuffers = videoCodec.getOutputBuffers();boolean isVideoEOS = false;long startMs = System.currentTimeMillis();while (!Thread.interrupted()) {if (!isPlaying) {continue;}//将资源传递到解码器if (!isVideoEOS) {isVideoEOS = putBufferToCoder(videoExtractor, videoCodec, inputBuffers);}int outputBufferIndex = videoCodec.dequeueOutputBuffer(videoBufferInfo, TIMEOUT_US);switch (outputBufferIndex) {case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:Log.v(TAG, "format changed");break;case MediaCodec.INFO_TRY_AGAIN_LATER:Log.v(TAG, "解码当前帧超时");break;case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED://outputBuffers = videoCodec.getOutputBuffers();Log.v(TAG, "output buffers changed");break;default://直接渲染到Surface时使用不到outputBuffer//ByteBuffer outputBuffer = outputBuffers[outputBufferIndex];//延时操作//如果缓冲区里的可展示时间>当前视频播放的进度，就休眠一下sleepRender(videoBufferInfo, startMs);//渲染videoCodec.releaseOutputBuffer(outputBufferIndex, true);break;}if ((videoBufferInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {Log.v(TAG, "buffer stream end");break;}}//end whilevideoCodec.stop();videoCodec.release();videoExtractor.release();}}

获取指定类型媒体文件所在轨道

    //获取指定类型媒体文件所在轨道private int getMediaTrackIndex(MediaExtractor videoExtractor, String MEDIA_TYPE) {int trackIndex = -1;for (int i = 0; i < videoExtractor.getTrackCount(); i++) {//获取视频所在轨道MediaFormat mediaFormat = videoExtractor.getTrackFormat(i);String mime = mediaFormat.getString(MediaFormat.KEY_MIME);if (mime.startsWith(MEDIA_TYPE)) {trackIndex = i;break;}}return trackIndex;}

将缓冲区传递至解码器

    //将缓冲区传递至解码器private boolean putBufferToCoder(MediaExtractor extractor, MediaCodec decoder, ByteBuffer[] inputBuffers) {boolean isMediaEOS = false;int inputBufferIndex = decoder.dequeueInputBuffer(TIMEOUT_US);if (inputBufferIndex >= 0) {ByteBuffer inputBuffer = inputBuffers[inputBufferIndex];int sampleSize = extractor.readSampleData(inputBuffer, 0);if (sampleSize < 0) {decoder.queueInputBuffer(inputBufferIndex, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);isMediaEOS = true;Log.v(TAG, "media eos");} else {decoder.queueInputBuffer(inputBufferIndex, 0, sampleSize, extractor.getSampleTime(), 0);extractor.advance();}}return isMediaEOS;}

音频的部分类似，完整源码请移步jiyangg/MediaPlaySimpleDemo