Android MediaCodec and MediaMuxer

Android MediaMuxer API 中有这样一段sample code
https://developer.android.com...

 MediaMuxer muxer = new MediaMuxer("temp.mp4", OutputFormat.MUXER_OUTPUT_MPEG_4);
 // More often, the MediaFormat will be retrieved from MediaCodec.getOutputFormat()
 // or MediaExtractor.getTrackFormat().
 MediaFormat audioFormat = new MediaFormat(...);
 MediaFormat videoFormat = new MediaFormat(...);
 int audioTrackIndex = muxer.addTrack(audioFormat);
 int videoTrackIndex = muxer.addTrack(videoFormat);
 ByteBuffer inputBuffer = ByteBuffer.allocate(bufferSize);
 boolean finished = false;
 BufferInfo bufferInfo = new BufferInfo();

 muxer.start();
 while(!finished) {
   // getInputBuffer() will fill the inputBuffer with one frame of encoded
   // sample from either MediaCodec or MediaExtractor, set isAudioSample to
   // true when the sample is audio data, set up all the fields of bufferInfo,
   // and return true if there are no more samples.
   finished = getInputBuffer(inputBuffer, isAudioSample, bufferInfo);
   if (!finished) {
     int currentTrackIndex = isAudioSample ? audioTrackIndex : videoTrackIndex;
     muxer.writeSampleData(currentTrackIndex, inputBuffer, bufferInfo);
   }
 };
 muxer.stop();
 muxer.release();
 

这段代码 finished = getInputBuffer(inputBuffer, isAudioSample, bufferInfo); 似乎不是API提供的函数，xref里没有搜到，是自定义的函数吗？还是新版本去掉了这个API？

Thanks