Anddroid媒体解码学习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

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


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 {
        @Override
        public 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 while
            videoCodec.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