[Android] MediaExtractor 和 MediaCodec 如何配合使用 - Video篇

MediaExtractor 是用來將來源的影音資料分開，
它支援HTTP streaming或者是local的檔案，
video和audio分開之後再丟給MediaCodec去decode，

首先看一下video部份，
video需要render，所以還另外需要加上SurfaceView，

private MediaExtractor extractorVideo;
private MediaCodec decoderVideo;

extractorVideo = new MediaExtractor();
extractorVideo.setDataSource("myTest.mp4"); 

for (int i = 0; i < extractorVideo.getTrackCount(); i++) {
 MediaFormat format = extractorVideo.getTrackFormat(i);
 String mime = format.getString(MediaFormat.KEY_MIME);
 Log.d(TAG, "mime=>"+mime);
 if (mime.startsWith("video/")) {
  videoTrack = i;  
  extractorVideo.selectTrack(videoTrack);
  decoderVideo = MediaCodec.createDecoderByType(mime);
  decoderVideo.configure(format, surface, null, 0);
  break;
 }
}

if (videoTrack >=0) {
 if(decoderVideo == null)
 {
  Log.e(TAG, "Can't find video info!");
  return;
 }
 else
  decoderVideo.start();
}

extractorVideo 會根據MIME的資訊把video track找出來，
把video format和surface透過decoderVideo.configure()傳給decoderVideo，
之後decoderVideo便會接手decode和render的工作，

 接下來就是decode部份：

ByteBuffer[] inputBuffersVideo=null;
ByteBuffer[] outputBuffersVideo=null;
BufferInfo infoVideo=null;

if (videoTrack >=0)
{
 inputBuffersVideo = decoderVideo.getInputBuffers();
 outputBuffersVideo = decoderVideo.getOutputBuffers();
 infoVideo = new BufferInfo();
}

boolean isEOS = false;
long startMs = System.currentTimeMillis();

while (!Thread.interrupted()) {
 if (videoTrack >=0)
 {     
  if (!isEOS) {      
   int inIndex=-1;
   try {
    inIndex = decoderVideo.dequeueInputBuffer(10000);
   } catch (Exception e) {
    e.printStackTrace();    
   }

   if (inIndex >= 0) {
    ByteBuffer buffer = inputBuffersVideo[inIndex];
    int sampleSize = extractorVideo.readSampleData(buffer, 0);
    if (sampleSize < 0) {
     // We shouldn't stop the playback at this point, just pass the EOS
     // flag to decoder, we will get it again from the dequeueOutputBuffer     
     decoderVideo.queueInputBuffer(inIndex, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
     buffer.clear();
     isEOS = true;
    } else {     
     long current = System.currentTimeMillis();
     decoderVideo.queueInputBuffer(inIndex, 0, sampleSize, extractorVideo.getSampleTime(), 0);     
     buffer.clear();
     extractorVideo.advance();
    }
   }
  }
  int outIndex=-1;
  try {
   outIndex = decoderVideo.dequeueOutputBuffer(infoVideo,10000);
  } catch (Exception e) {
   e.printStackTrace();   
  }
  switch (outIndex) {
  case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
   Log.d(TAG, "INFO_OUTPUT_BUFFERS_CHANGED");
   outputBuffersVideo = decoderVideo.getOutputBuffers();
   break;
  case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
   Log.d(TAG, "New format " + decoderVideo.getOutputFormat());
   break;
  case MediaCodec.INFO_TRY_AGAIN_LATER:
   Log.d(TAG, "dequeueOutputBuffer timed out!");
   break;
  default:
   if(outIndex >=0)
   {
    ByteBuffer buffer = outputBuffersVideo[outIndex];    
    buffer.clear();
    decoderVideo.releaseOutputBuffer(outIndex, true);
    // We use a very simple clock to keep the video FPS, or the video
    // playback will be too fast
    while (infoVideo.presentationTimeUs / 1000 > (System.currentTimeMillis() - startMs)) {
     try {      
      sleep(10);
     } catch (InterruptedException e) {
      e.printStackTrace();
      Thread.currentThread().interrupt();
      break;
     }
    }
   }
   break;
  }

  // All decoded frames have been rendered, we can stop playing now
  if ((infoVideo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
   Log.d(TAG, "OutputBuffer BUFFER_FLAG_END_OF_STREAM");
   break;
  }
 }
}
if (videoTrack >=0)
{
 decoderVideo.stop();
 decoderVideo.release();
}

extractorVideo.release();

先呼叫decoderVideo.dequeueInputBuffer(10000)取得一個input buffer，
利用extractorVideo.readSampleData(buffer, 0)將資料放到buffer去，
然後再呼叫decoderVideo.queueInputBuffer()將資料queue到後面的decode工作， decoderVideo.dequeueOutputBuffer(infoVideo,10000)如果傳回非-1的值，
表示decode成功，
然後透過decoderVideo.releaseOutputBuffer(outIndex, true)將它render到surface，
這樣video的工作就完成了