Android硬编解码接口MediaCodec使用完全解析（一）

0、本文概述

MediaCodec是android api 16以后开放的硬编解码接口，英文文档参照这个链接，中文翻译可以参考这个链接。本文主要记录的是如何使用MediaCodec对视频进行编解码，最后会以实例的方式展示如何将Camera预览数据编码成H264，再把编码后的h264解码并且显示在SurfaceView中。本例不涉及音频的编解码。

1、MediaCodec编码视频

使用MediaCodec实现视频编码的步骤如下：
1.初始化MediaCodec，方法有两种，分别是通过名称和类型来创建，对应的方法为：

MediaCodec createByCodecName (String name);
MediaCodec createDecoderByType (String type);

具体可用的name和type参考文档即可。这里我们通过后者来初始化一个视频编码器。

mMC = MediaCodec.createDecoderByType(MIME_TYPE);

2.配置MediaCodec，这一步需要配置的是MediaFormat，这个类包含了比特率、帧率、关键帧间隔时间等，其中比特率如果太低就会造成类似马赛克的现象。

mMF = MediaFormat.createVideoFormat(MIME_TYPE, width, height);
mMF.setInteger(MediaFormat.KEY_BIT_RATE, bitrate);  
mMF.setInteger(MediaFormat.KEY_FRAME_RATE, framerate);  
if (mPrimeColorFormat != 0){
    mMF.setInteger(MediaFormat.KEY_COLOR_FORMAT, mPrimeColorFormat);  
}
mMF.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, 1); //关键帧间隔时间 单位s
mMC.configure(mMF, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);

其中mPrimeColorFormat为本机支持的颜色空间。一般是yuv420p或者yuv420sp，Camera预览格式一般是yv12或者NV21，所以在编码之前需要进行格式转换，实例可参照文末代码。代码是最好的老师嘛。
3.打开编码器，获取输入输出缓冲区

mMC.start();
mInputBuffers = mMC.getInputBuffers();
mOutputBuffers = mMC.getOutputBuffers();

4.输入数据，过程可以分为以下几个小步：
1）获取可使用缓冲区位置得到索引

int inputbufferindex = mMC.dequeueInputBuffer(BUFFER_TIMEOUT);

如果存在可用的缓冲区，此方法会返回其位置索引，否则返回-1，参数为超时时间，单位是毫秒，如果此参数是0，则立即返回，如果参数小于0，则无限等待直到有可使用的缓冲区，如果参数大于0，则等待时间为传入的毫秒值。
2）传入原始数据

ByteBuffer inputBuffer = mInputBuffers[inputbufferindex];
inputBuffer.clear();//清除原来的内容以接收新的内容
inputBuffer.put(bytes, 0, len);//len是传进来的有效数据长度
mMC.queueInputBuffer(inputbufferindex, 0, len, timestamp, 0);

此缓冲区一旦使用，只有在dequeueInputBuffer返回其索引位置才代表它可以再次使用。
5.获取其输出数据，获取输入原始数据和获取输出数据最好是异步进行，因为输入一帧数据不代表编码器马上就会输出对应的编码数据，可能输入好几帧才会输出一帧。获取输出数据的步骤与输入数据的步骤相似：
1）获取可用的输出缓冲区

int outputbufferindex = mMC.dequeueOutputBuffer(mBI, BUFFER_TIMEOUT);

其中参数一是一个BufferInfo类型的实例，参数二为超时时间，负数代表无限等待（可见，不要在主线程进行操作）。
2）获取输出数据

mOutputBuffers[outputbufferindex].get(bytes, 0, mBI.size);

3）释放缓冲区

mMC.releaseOutputBuffer(outputbufferindex, false);

2、MediaCodec解码视频

解码视频的步骤跟编码的类似，配置不一样：
1.实例化解码器

mMC = MediaCodec.createDecoderByType(MIME_TYPE);

2.配置解码器，此处需要配置用于显示图像的Surface、MediaFormat包含视频的pps和sps（包含在编码出来的第一帧数据）

int[] width = new int[1];
int[] height = new int[1];  
AvcUtils.parseSPS(sps, width, height);//从sps中解析出视频宽高
mMF = MediaFormat.createVideoFormat(MIME_TYPE, width[0], height[0]);
mMF.setByteBuffer("csd-0", ByteBuffer.wrap(sps));
mMF.setByteBuffer("csd-1", ByteBuffer.wrap(pps));
mMF.setInteger(MediaFormat.KEY_MAX_INPUT_SIZE, width[0] * height[0]);
mMC.configure(mMF, surface, null, 0);

3.开启编码器并获取输入输出缓冲区

mMC.start();
mInputBuffers = mMC.getInputBuffers();
mOutputBuffers = mMC.getOutputBuffers();

4.输入数据
1）获取可用的输入缓冲区

int inputbufferindex = mMC.dequeueInputBuffer(BUFFER_TIMEOUT);

返回值为可用缓冲区的索引

ByteBuffer inputBuffer = mInputBuffers[inputbufferindex];
inputBuffer.clear();

2）然后输入数据

inputBuffer.put(bytes, 0, len);
mMC.queueInputBuffer(inputbufferindex, 0, len, timestamp, 0);

5.获取输出数据，这一步与4同样应该异步进行，其具体步骤与上面解码的基本相同，在释放缓冲区的时候需要注意第二个参数设置为true，表示解码显示在Surface上

mMC.releaseOutputBuffer(outputbufferindex, true);

3、编解码实例

下面是一个MediaCodec编解码实例，此例子Camera预览数据（yv12）编码成H264，再把编码后的h264解码并且显示在SurfaceView中。
##3.1布局文件
布局文件非常简单，两个SurfaceView分别用于显示编解码的图像，两个按钮控制开始和停止，一个TextView用于显示捕捉帧率。布局文件代码就不展示了，界面如下

3.2编码器类Encoder

package com.example.mediacodecpro;

import android.media.MediaCodec;
import android.media.MediaCodecInfo;
import android.media.MediaFormat;
import android.util.Log;

import java.io.IOException;
import java.nio.ByteBuffer;

/**
 * Created by chuibai on 2017/3/10.

 */

public class Encoder {

    public static final int TRY_AGAIN_LATER = -1;
    public static final int BUFFER_OK = 0;
    public static final int BUFFER_TOO_SMALL = 1;
    public static final int OUTPUT_UPDATE = 2;

    private int format = 0;
    private final String MIME_TYPE = "video/avc";
    private MediaCodec mMC = null;
    private MediaFormat mMF;
    private ByteBuffer[] inputBuffers;
    private ByteBuffer[] outputBuffers;
    private long BUFFER_TIMEOUT = 0;
    private MediaCodec.BufferInfo mBI;

    /**
     * 初始化编码器
     * @throws IOException 创建编码器失败会抛出异常
     */
    public void init() throws IOException {
        mMC = MediaCodec.createEncoderByType(MIME_TYPE);
        format = MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420Planar;
        mBI = new MediaCodec.BufferInfo();
    }

    /**
     * 配置编码器，需要配置颜色、帧率、比特率以及视频宽高
     * @param width 视频的宽
     * @param height 视频的高
     * @param bitrate 视频比特率
     * @param framerate 视频帧率
     */
    public void configure(int width,int height,int bitrate,int framerate){
        if(mMF == null){
            mMF = MediaFormat.createVideoFormat(MIME_TYPE, width, height);
            mMF.setInteger(MediaFormat.KEY_BIT_RATE, bitrate);
            mMF.setInteger(MediaFormat.KEY_FRAME_RATE, framerate);
            if (format != 0){
                mMF.setInteger(MediaFormat.KEY_COLOR_FORMAT, format);
            }
            mMF.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, -1); //关键帧间隔时间 单位s
        }
        mMC.configure(mMF,null,null,MediaCodec.CONFIGURE_FLAG_ENCODE);
    }

    /**
     * 开启编码器，获取输入输出缓冲区
     */
    public void start(){
        mMC.start();
        inputBuffers = mMC.getInputBuffers();
        outputBuffers = mMC.getOutputBuffers();
    }

    /**
     * 向编码器输入数据，此处要求输入YUV420P的数据
     * @param data YUV数据
     * @param len 数据长度
     * @param timestamp 时间戳
     * @return
     */
    public int input(byte[] data,int len,long timestamp){
        int index = mMC.dequeueInputBuffer(BUFFER_TIMEOUT);
        Log.e("...","" + index);
        if(index >= 0){
            ByteBuffer inputBuffer = inputBuffers[index];
            inputBuffer.clear();
            if(inputBuffer.capacity() < len){
                mMC.queueInputBuffer(index, 0, 0, timestamp, 0);
                return BUFFER_TOO_SMALL;
            }
            inputBuffer.put(data,0,len);
            mMC.queueInputBuffer(index,0,len,timestamp,0);
        }else{
            return index;
        }
        return BUFFER_OK;
    }

    /**
     * 输出编码后的数据
     * @param data 数据
     * @param len 有效数据长度
     * @param ts 时间戳
     * @return
     */
    public int output(/*out*/byte[] data,/* out */int[] len,/* out */long[] ts){
        int i = mMC.dequeueOutputBuffer(mBI, BUFFER_TIMEOUT);
        if(i >= 0){
            if(mBI.size > data.length) return BUFFER_TOO_SMALL;
            outputBuffers[i].position(mBI.offset);
            outputBuffers[i].limit(mBI.offset + mBI.size);
            outputBuffers[i].get(data, 0, mBI.size);
            len[0] = mBI.size ;
            ts[0] = mBI.presentationTimeUs;
            mMC.releaseOutputBuffer(i, false);
        } else if (i == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
            outputBuffers = mMC.getOutputBuffers();
            return OUTPUT_UPDATE;
        } else if (i == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
            mMF = mMC.getOutputFormat();
            return OUTPUT_UPDATE;
        } else if (i == MediaCodec.INFO_TRY_AGAIN_LATER) {
            return TRY_AGAIN_LATER;
        }

        return BUFFER_OK;
    }

    public void release(){
        mMC.stop();
        mMC.release();
        mMC = null;
        outputBuffers = null;
        inputBuffers = null;
    }

    public void flush() {
        mMC.flush();
    }
}

3.3解码器类Decoder

package com.example.mediacodecpro;

import android.media.MediaCodec;
import android.media.MediaFormat;
import android.view.Surface;
import java.io.IOException;
import java.nio.ByteBuffer;

/**
 * Created by chuibai on 2017/3/10.

 */

public class Decoder {

    public static final int TRY_AGAIN_LATER = -1;
    public static final int BUFFER_OK = 0;
    public static final int BUFFER_TOO_SMALL = 1;
    public static final int OUTPUT_UPDATE = 2;

    private final String MIME_TYPE = "video/avc";
    private MediaCodec mMC = null;
    private MediaFormat mMF;
    private long BUFFER_TIMEOUT = 0;
    private MediaCodec.BufferInfo mBI;
    private ByteBuffer[] mInputBuffers;
    private ByteBuffer[] mOutputBuffers;

    /**
     * 初始化编码器
     * @throws IOException 创建编码器失败会抛出异常
     */
    public void init() throws IOException {
        mMC = MediaCodec.createDecoderByType(MIME_TYPE);
        mBI = new MediaCodec.BufferInfo();
    }

    /**
     * 配置解码器
     * @param sps 用于配置的sps参数
     * @param pps 用于配置的pps参数
     * @param surface 用于解码显示的Surface
     */
    public void configure(byte[] sps, byte[] pps, Surface surface){
        int[] width = new int[1];
        int[] height = new int[1];
        AvcUtils.parseSPS(sps, width, height);//从sps中解析出视频宽高
        mMF = MediaFormat.createVideoFormat(MIME_TYPE, width[0], height[0]);
        mMF.setByteBuffer("csd-0", ByteBuffer.wrap(sps));
        mMF.setByteBuffer("csd-1", ByteBuffer.wrap(pps));
        mMF.setInteger(MediaFormat.KEY_MAX_INPUT_SIZE, width[0] * height[0]);
        mMC.configure(mMF, surface, null, 0);
    }

    /**
     * 开启解码器，获取输入输出缓冲区
     */
    public void start(){
        mMC.start();
        mInputBuffers = mMC.getInputBuffers();
        mOutputBuffers = mMC.getOutputBuffers();
    }

    /**
     * 输入数据
     * @param data 输入的数据
     * @param len 数据有效长度
     * @param timestamp 时间戳
     * @return 成功则返回{@link #BUFFER_OK} 否则返回{@link #TRY_AGAIN_LATER}
     */
    public int input(byte[] data,int len,long timestamp){
        int i = mMC.dequeueInputBuffer(BUFFER_TIMEOUT);
        if(i >= 0){
            ByteBuffer inputBuffer = mInputBuffers[i];
            inputBuffer.clear();
            inputBuffer.put(data, 0, len);
            mMC.queueInputBuffer(i, 0, len, timestamp, 0);
        }else {
            return TRY_AGAIN_LATER;
        }
        return BUFFER_OK;
    }

    public int output(byte[] data,int[] len,long[] ts){
        int i = mMC.dequeueOutputBuffer(mBI, BUFFER_TIMEOUT);
        if(i >= 0){
            if (mOutputBuffers[i] != null)
            {
                mOutputBuffers[i].position(mBI.offset);
                mOutputBuffers[i].limit(mBI.offset + mBI.size);

                if (data != null)
                    mOutputBuffers[i].get(data, 0, mBI.size);
                len[0] = mBI.size;
                ts[0] = mBI.presentationTimeUs;
            }
            mMC.releaseOutputBuffer(i, true);
        }else{
            return TRY_AGAIN_LATER;
        }
        return BUFFER_OK;
    }

    public void flush(){
        mMC.flush();
    }

    public void release() {
        flush();
        mMC.stop();
        mMC.release();
        mMC = null;
        mInputBuffers = null;
        mOutputBuffers = null;
    }
}

3.4MainAcitivity

package com.example.mediacodecpro;

import android.content.pm.ActivityInfo;
import android.graphics.ImageFormat;
import android.hardware.Camera;
import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.io.IOException;
import java.io.OutputStream;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Queue;
import butterknife.BindView;
import butterknife.ButterKnife;

public class MainActivity extends AppCompatActivity implements View.OnClickListener, Camera.PreviewCallback {

    @BindView(R.id.surfaceView_encode)
    SurfaceView surfaceViewEncode;
    @BindView(R.id.surfaceView_decode)
    SurfaceView surfaceViewDecode;
    @BindView(R.id.btnStart)
    Button btnStart;
    @BindView(R.id.btnStop)
    Button btnStop;
    @BindView(R.id.capture)
    TextView capture;
    private int width;
    private int height;
    private int bitrate;
    private int framerate;
    private int captureFrame;
    private Camera mCamera;
    private Queue mPreviewBuffers_clean;
    private Queue mPreviewBuffers_dirty;
    private Queue mDecodeBuffers_clean;
    private Queue mDecodeBuffers_dirty;
    private int PREVIEW_POOL_CAPACITY = 5;
    private int format;
    private int DECODE_UNI_SIZE = 1024 * 1024;
    private byte[] mAvcBuf = new byte[1024 * 1024];
    private final int MSG_ENCODE = 0;
    private final int MSG_DECODE = 1;
    private String TAG = "MainActivity";
    private long mLastTestTick = 0;
    private Object mAvcEncLock;
    private Object mDecEncLock;
    private Decoder mDecoder;
    private Handler codecHandler;
    private byte[] mRawData;
    private Encoder mEncoder;
    private CodecThread codecThread;
    private DatagramSocket socket;
    private DatagramPacket packet;
    private byte[] sps_pps;
    private byte[] mPacketBuf = new byte[1024 * 1024];


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);

        //初始化参数
        initParams();

        //设置监听事件
        btnStart.setOnClickListener(this);
        btnStop.setOnClickListener(this);
    }

    /**
     * 初始化参数，包括帧率、颜色、比特率，视频宽高等
     */
    private void initParams() {
        width = 352;
        height = 288;
        bitrate = 1500000;
        framerate = 30;
        captureFrame = 0;
        format = ImageFormat.YV12;
        mAvcEncLock = new Object();
        mDecEncLock = new Object();
    }

    @Override
    protected void onResume() {
        if (getRequestedOrientation() != ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE) {
            setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
        }
        super.onResume();
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.btnStart:
                mCamera = Camera.open(0);
                initQueues();
                initEncoder();
                initCodecThread();
                startPreview();
                break;
            case R.id.btnStop:
                releaseCodecThread();
                releseEncoderAndDecoder();
                releaseCamera();
                releaseQueue();
                break;
        }
    }

    /**
     * 释放队列资源
     */
    private void releaseQueue() {
        if (mPreviewBuffers_clean != null){
            mPreviewBuffers_clean.clear();
            mPreviewBuffers_clean = null;
        }
        if (mPreviewBuffers_dirty != null){
            mPreviewBuffers_dirty.clear();
            mPreviewBuffers_dirty = null;
        }
        if (mDecodeBuffers_clean != null){
            mDecodeBuffers_clean.clear();
            mDecodeBuffers_clean = null;
        }
        if (mDecodeBuffers_dirty != null){
            mDecodeBuffers_dirty.clear();
            mDecodeBuffers_dirty = null;
        }
    }

    /**
     * 释放摄像头资源
     */
    private void releaseCamera() {
        if(mCamera != null){
            mCamera.setPreviewCallbackWithBuffer(null);
            mCamera.stopPreview();
            mCamera.release();
            mCamera = null;
        }
    }

    private void releseEncoderAndDecoder() {
        if(mEncoder != null){
            mEncoder.flush();
            mEncoder.release();
            mEncoder = null;
        }
        if(mDecoder != null){
            mDecoder.release();
            mDecoder = null;
        }
    }

    private void releaseCodecThread() {
        codecHandler.getLooper().quit();
        codecHandler = null;
        codecThread = null;
    }

    private void initCodecThread() {
        codecThread = new CodecThread();
        codecThread.start();
    }

    /**
     * 开启预览
     */
    private void startPreview() {
        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setPreviewFormat(format);
        parameters.setPreviewFrameRate(framerate);
        parameters.setPreviewSize(width,height);
        mCamera.setParameters(parameters);
        try {
            mCamera.setPreviewDisplay(surfaceViewEncode.getHolder());
        } catch (IOException e) {
            e.printStackTrace();
        }
        mCamera.setPreviewCallbackWithBuffer(this);
        mCamera.startPreview();
    }

    @Override
    public void onPreviewFrame(byte[] data, Camera camera) {
        /** 预览的data为null */
        if(data == null) {
            Log.e(TAG,"预览的data为null");
            return;
        }

        long curTick = System.currentTimeMillis();
        if (mLastTestTick == 0) {
            mLastTestTick = curTick;
        }
        if (curTick > mLastTestTick + 1000) {
            setCaptureFPSTextView(captureFrame);
            captureFrame = 0;
            mLastTestTick = curTick;
        } else
            captureFrame++;
        synchronized(mAvcEncLock) {
            PreviewBufferInfo info = mPreviewBuffers_clean.poll();    //remove the head of queue
            info.buffer = data;
            info.size = getPreviewBufferSize(width, height, format);
            info.timestamp = System.currentTimeMillis();
            mPreviewBuffers_dirty.add(info);
            if(mDecoder == null){
                codecHandler.sendEmptyMessage(MSG_ENCODE);
            }
        }
    }

    private void setCaptureFPSTextView(int captureFrame) {
        capture.setText("当前帧率：" + captureFrame);
    }

    private void initEncoder() {
        mEncoder = new Encoder();
        try {
            mEncoder.init();
            mEncoder.configure(width,height,bitrate,framerate);
            mEncoder.start();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    /**
     * 初始化各种队列
     */
    private void initQueues() {
        if (mPreviewBuffers_clean == null)
            mPreviewBuffers_clean = new LinkedList<>();
        if (mPreviewBuffers_dirty == null)
            mPreviewBuffers_dirty = new LinkedList<>();
        int size = getPreviewBufferSize(width, height, format);
        for (int i = 0; i < PREVIEW_POOL_CAPACITY; i++) {
            byte[] mem = new byte[size];
            mCamera.addCallbackBuffer(mem);    //ByteBuffer.array is a reference, not a copy
            PreviewBufferInfo info = new PreviewBufferInfo();
            info.buffer = null;
            info.size = 0;
            info.timestamp = 0;
            mPreviewBuffers_clean.add(info);
        }
        if (mDecodeBuffers_clean == null)
            mDecodeBuffers_clean = new LinkedList<>();
        if (mDecodeBuffers_dirty == null)
            mDecodeBuffers_dirty = new LinkedList<>();
        for (int i = 0; i < PREVIEW_POOL_CAPACITY; i++) {
            PreviewBufferInfo info = new PreviewBufferInfo();
            info.buffer = new byte[DECODE_UNI_SIZE];
            info.size = 0;
            info.timestamp = 0;
            mDecodeBuffers_clean.add(info);
        }
    }

    /**
     * 获取预览buffer的大小
     * @param width 预览宽
     * @param height 预览高
     * @param format 预览颜色格式
     * @return 预览buffer的大小
     */
    private int getPreviewBufferSize(int width, int height, int format) {
        int size = 0;
        switch (format) {
            case ImageFormat.YV12: {
                int yStride = (int) Math.ceil(width / 16.0) * 16;
                int uvStride = (int) Math.ceil((yStride / 2) / 16.0) * 16;
                int ySize = yStride * height;
                int uvSize = uvStride * height / 2;
                size = ySize + uvSize * 2;
            }
            break;

            case ImageFormat.NV21: {
                float bytesPerPix = (float) ImageFormat.getBitsPerPixel(format) / 8;
                size = (int) (width * height * bytesPerPix);
            }
            break;
        }

        return size;
    }

    private void swapYV12toI420(byte[] yv12bytes, byte[] i420bytes, int width, int height) {
        System.arraycopy(yv12bytes, 0, i420bytes, 0, width * height);
        System.arraycopy(yv12bytes, width * height + width * height / 4, i420bytes, width * height, width * height / 4);
        System.arraycopy(yv12bytes, width * height, i420bytes, width * height + width * height / 4, width * height / 4);
    }

    private class PreviewBufferInfo {
        public byte[] buffer;
        public int size;
        public long timestamp;
    }

    private class CodecThread extends Thread {
        @Override
        public void run() {
            Looper.prepare();
            codecHandler = new Handler() {
                @Override
                public void handleMessage(Message msg) {
                    switch (msg.what) {
                        case MSG_ENCODE:
                            int res = Encoder.BUFFER_OK;
                            synchronized (mAvcEncLock) {
                                if (mPreviewBuffers_dirty != null && mPreviewBuffers_clean != null) {
                                    Iterator ite = mPreviewBuffers_dirty.iterator();
                                    while (ite.hasNext()) {
                                        PreviewBufferInfo info = ite.next();
                                        byte[] data = info.buffer;
                                        int data_size = info.size;
                                        if (format == ImageFormat.YV12) {
                                            if (mRawData == null || mRawData.length < data_size) {
                                                mRawData = new byte[data_size];
                                            }
                                            swapYV12toI420(data, mRawData, width, height);
                                        } else {
                                            Log.e(TAG, "preview size MUST be YV12, cur is " + format);
                                            mRawData = data;
                                        }
                                        res = mEncoder.input(mRawData, data_size, info.timestamp);
                                        if (res != Encoder.BUFFER_OK) {
//                                            Log.e(TAG, "mEncoder.input, maybe wrong:" + res);
                                            break;        //the rest buffers shouldn't go into encoder, if the previous one get problem
                                        } else {
                                            ite.remove();
                                            mPreviewBuffers_clean.add(info);
                                            if (mCamera != null) {
                                                mCamera.addCallbackBuffer(data);
                                            }
                                        }
                                    }
                                }
                            }


                            while (res == Encoder.BUFFER_OK) {
                                int[] len = new int[1];
                                long[] ts = new long[1];
                                synchronized (mAvcEncLock) {
                                    res = mEncoder.output(mAvcBuf, len, ts);
                                }

                                if (res == Encoder.BUFFER_OK) {
                                    //发送h264
                                    if(sps_pps != null){
                                        send(len[0]);
                                    }

                                    if (mDecodeBuffers_clean != null && mDecodeBuffers_dirty != null) {
                                        synchronized (mAvcEncLock) {
                                            Iterator ite = mDecodeBuffers_clean.iterator();
                                            if (ite.hasNext()) {
                                                PreviewBufferInfo bufferInfo = ite.next();
                                                if (bufferInfo.buffer.length >= len[0]) {
                                                    bufferInfo.timestamp = ts[0];
                                                    bufferInfo.size = len[0];
                                                    System.arraycopy(mAvcBuf, 0, bufferInfo.buffer, 0, len[0]);
                                                    ite.remove();
                                                    mDecodeBuffers_dirty.add(bufferInfo);
                                                } else {
                                                    Log.e(TAG, "decoder uni buffer too small, need " + len[0] + " but has " + bufferInfo.buffer.length);
                                                }
                                            }
                                        }
                                        initDecoder(len);
                                    }
                                }

                            }
                            codecHandler.sendEmptyMessageDelayed(MSG_ENCODE, 30);
                            break;

                        case MSG_DECODE:
                            synchronized (mDecEncLock) {
                                int result = Decoder.BUFFER_OK;

                                //STEP 1: handle input buffer
                                if (mDecodeBuffers_dirty != null && mDecodeBuffers_clean != null) {
                                    Iterator ite = mDecodeBuffers_dirty.iterator();
                                    while (ite.hasNext()) {
                                        PreviewBufferInfo info = ite.next();
                                        result = mDecoder.input(info.buffer, info.size, info.timestamp);
                                        if (result != Decoder.BUFFER_OK) {
                                            break;        //the rest buffers shouldn't go into encoder, if the previous one get problem
                                        } else {
                                            ite.remove();
                                            mDecodeBuffers_clean.add(info);
                                        }
                                    }
                                }

                                int[] len = new int[1];
                                long[] ts = new long[1];
                                while (result == Decoder.BUFFER_OK) {
                                    result = mDecoder.output(null, len, ts);
                                }
                            }
                            codecHandler.sendEmptyMessageDelayed(MSG_DECODE, 30);
                            break;
                    }
                }
            };
            Looper.loop();
        }
    }

    private void send(int len) {
        try {
            if(socket == null) socket = new DatagramSocket();
            if(packet == null){
                packet = new DatagramPacket(mPacketBuf,0,sps_pps.length + len);
                packet.setAddress(InetAddress.getByName("192.168.43.1"));
                packet.setPort(5006);
            }
            if(mAvcBuf[4] == 0x65){
                System.arraycopy(sps_pps,0,mPacketBuf,0,sps_pps.length);
                System.arraycopy(mAvcBuf,0,mPacketBuf,sps_pps.length,len);
                len += sps_pps.length;
            }else{
                System.arraycopy(mAvcBuf,0,mPacketBuf,0,len);
            }
            packet.setLength(len);
            socket.send(packet);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void initDecoder(int[] len) {
        if(sps_pps == null){
            sps_pps = new byte[len[0]];
            System.arraycopy(mAvcBuf,0,sps_pps,0,len[0]);
        }
        if(mDecoder == null){
            mDecoder = new Decoder();
            try {
                mDecoder.init();
            } catch (IOException e) {
                e.printStackTrace();
            }
            byte[] sps_nal = null;
            int sps_len = 0;
            byte[] pps_nal = null;
            int pps_len = 0;
            ByteBuffer byteb = ByteBuffer.wrap(mAvcBuf, 0, len[0]);
            //SPS
            if (true == AvcUtils.goToPrefix(byteb)) {
                int sps_position = 0;
                int pps_position = 0;
                int nal_type = AvcUtils.getNalType(byteb);
                if (AvcUtils.NAL_TYPE_SPS == nal_type) {
                    Log.d(TAG, "OutputAvcBuffer, AVC NAL type: SPS");
                    sps_position = byteb.position() - AvcUtils.START_PREFIX_LENGTH - AvcUtils.NAL_UNIT_HEADER_LENGTH;
                    //PPS
                    if (true == AvcUtils.goToPrefix(byteb)) {
                        nal_type = AvcUtils.getNalType(byteb);
                        if (AvcUtils.NAL_TYPE_PPS == nal_type) {
                            pps_position = byteb.position() - AvcUtils.START_PREFIX_LENGTH - AvcUtils.NAL_UNIT_HEADER_LENGTH;
                            sps_len = pps_position - sps_position;
                            sps_nal = new byte[sps_len];
                            int cur_pos = byteb.position();
                            byteb.position(sps_position);
                            byteb.get(sps_nal, 0, sps_len);
                            byteb.position(cur_pos);
                            //slice
                            if (true == AvcUtils.goToPrefix(byteb)) {
                                nal_type = AvcUtils.getNalType(byteb);
                                int pps_end_position = byteb.position() - AvcUtils.START_PREFIX_LENGTH - AvcUtils.NAL_UNIT_HEADER_LENGTH;
                                pps_len = pps_end_position - pps_position;
                            } else {
                                pps_len = byteb.position() - pps_position;
                                //pps_len = byteb.limit() - pps_position + 1;
                            }
                            if (pps_len > 0) {
                                pps_nal = new byte[pps_len];
                                cur_pos = byteb.position();
                                byteb.position(pps_position);
                                byteb.get(pps_nal, 0, pps_len);
                                byteb.position(cur_pos);
                            }
                        } else {
                            //Log.d(log_tag, "OutputAvcBuffer, AVC NAL type: "+nal_type);
                            throw new UnsupportedOperationException("SPS is not followed by PPS, nal type :" + nal_type);
                        }
                    }
                } else {
                    //Log.d(log_tag, "OutputAvcBuffer, AVC NAL type: "+nal_type);
                }

                //2. configure AVC decoder with SPS/PPS
                if (sps_nal != null && pps_nal != null) {

                    int[] width = new int[1];
                    int[] height = new int[1];
                    AvcUtils.parseSPS(sps_nal, width, height);
                    mDecoder.configure(sps_nal, pps_nal,surfaceViewDecode.getHolder().getSurface());
                    mDecoder.start();
                    if (codecHandler != null) {
                        codecHandler.sendEmptyMessage(MSG_DECODE);
                    }
                }

            }
        }
    }

}

上面的send方法可以把手机捕捉并编码的视频数据发送到电脑上使用ffplay播放，使用ffplay的时候记得加上参数-analyzeduration 200000减小视频延迟。

4.要点总结

个人总结使用MediaCodec编解码的时候主要需要注意以下事项：

• 数据的输入和输出要异步进行，不要采用阻塞的方式等待输出数据
• 编码Camera预览数据的时候使用带buffer的预览回调，避免帧率过低
• 适当使用缓存队列，不要每一帧都new一个byte数组，避免频繁的GC
• 不要在主线程进行操作，在我学习的过程中看到有些朋友直接在预览回调里进行编解码，在dequeueOutputBuffer方法还传递-1，也就是无限等待程序返回