本文概述
MediaCodec是anroid api 16以后开发的硬编解码接口，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);- 1
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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);- 1
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);- 1
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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();- 1
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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);- 1
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);- 1
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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);- 1
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);- 1
3）释放缓冲区
mMC.releaseOutputBuffer(outputbufferindex, false);- 1
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);- 1
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);- 1
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3.开启编码器并获取输入输出缓冲区
mMC.start();
mInputBuffers = mMC.getInputBuffers();
mOutputBuffers = mMC.getOutputBuffers();- 1
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4.输入数据
1）获取可用的输入缓冲区
int inputbufferindex = mMC.dequeueInputBuffer(BUFFER_TIMEOUT);- 1
返回值为可用缓冲区的索引
ByteBuffer inputBuffer = mInputBuffers[inputbufferindex];
inputBuffer.clear();- 1
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2）然后输入数据
inputBuffer.put(bytes, 0, len);
mMC.queueInputBuffer(inputbufferindex, 0, len, timestamp, 0);- 1
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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);- 1
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(); } }- 1
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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; } }- 1
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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);