Andrdoid MediaCodec OutputBuffer approach method

Question

I am using Mediacodec on Android for H264 stream Decoding. The raw data stream consists of a series of NAL Units. Every frame(640*480) in the video is divided into four parts in the stream.

Each time I send a buffer(One NAL Unit) into Mediacodec Decoder and wait for the outputbuffer.

It turns out that the outputbuffer capacity is as big as a YUV Frame,but the number of outputbuffers that come up is nearly four times the Frame number.I guess the outputbuffer only returns 1/4 of the decode result.If it is so ,how can I get continuous YUV Frame Data ?

public void setDataToDecoder(byte[] videoBuffer,int size,int id){
        Log.e("Decoder","-----------"+id);
        inputBufferIndex = mediaCodec.dequeueInputBuffer(-1);
        //Log.e("Decoder","InputIndex "+inputBufferIndex);
        if(inputBufferIndex>=0){
            ByteBuffer inputBuffer=inputBuffers[inputBufferIndex];
            inputBuffer.clear();
            inputBuffer.put(videoBuffer,0,size);
            mediaCodec.queueInputBuffer(inputBufferIndex, 0, size, timeStamp, 0);
            timeStamp++;
        }
        BufferInfo bufferInfo = new BufferInfo();
        outputBufferIndex = mediaCodec.dequeueOutputBuffer(bufferInfo, 0);
        while(outputBufferIndex>=0){
            ByteBuffer outputData=outputBuffers[outputBufferIndex];
            if(bufferInfo.size!=0){
                outputData.position(bufferInfo.offset);
                outputData.limit(bufferInfo.offset+bufferInfo.size);
                Log.e("P","oooo"+outputData.position());
                Log.e("P","oooo"+outputData.limit());
            }
            int tmp;
            if(FrameCt<=20){
                try {
                    tmp = fc.write(outputData);
                    Log.e("P",""+tmp);
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            FrameCt++;
            mediaCodec.releaseOutputBuffer(outputBufferIndex, false);
            outputBufferIndex = mediaCodec.dequeueOutputBuffer(bufferInfo, 0);
        }
        Log.e("Decoder","-----------"+id);
    }