视频编解码技术初探

一、需要阅读的文章
        https://blog.csdn.net/feifeiwendao/article/details/52527824

        ####MediaCodec类相关的文章：########
        https://www.cnblogs.com/renhui/p/7478527.html

        https://blog.csdn.net/junzia/article/details/54018671    （思路很清晰的一篇文章）

        https://www.cnblogs.com/roger-yu/p/5635494.html

        https://www.cnblogs.com/Sharley/p/5964490.html

        https://blog.csdn.net/leif_/article/details/50971616

        MediaCodec实际上就是一个编解码的容器，将byte[]放进去，取出来就得到自己想要的编码格式的byte[]，然后
        写入文件即可。

        #########AudioRecorder录音：###################
        https://blog.csdn.net/qq_36982160/article/details/79383046

        https://www.cnblogs.com/whoislcj/p/5477216.html

        录音的流程：
        1）初始化AudioRecorder
        2）调用AudioRecorder的startRecording方法
        3）调用AudioRecorder的read方法，读出byte[]数据。你可以选择将数据存储到文件，最终得到的是.pcm文件。
             这种文件一般播放器不支持，需要用andorid的AudioTrack去播放。

        AudioTrack，播放PCM音频文件。
        https://www.cnblogs.com/stnlcd/p/7151438.html
        注意：AudioTrack的构造参数，要与录制时的参数保持一致 。如channelConfig如果不对应
        则人说话的声音就超级奇怪了。

        以下是PCM录音和播放的源码： 

package com.xinyi.czsuperrecorder;
import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioRecord;
import android.media.AudioTrack;
import android.media.MediaCodec;
import android.media.MediaCodecInfo;
import android.media.MediaFormat;
import android.media.MediaRecorder;
import android.util.Log;

import com.xinyi.baselib.io.tf.TFileHelper;

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

/**
 * Created by XinYi on 2018/7/5.
 * （录音API）
 */
public class AudioRecorder {
    private static final String TAG = "AudioRecorder";
    private int sampleRate=44100;   //采样率，默认44.1k
    private int channelConfig= AudioFormat.CHANNEL_IN_STEREO;        //通道设置，默认立体声
    private int audioFormat=AudioFormat.ENCODING_PCM_16BIT;     //设置采样数据格式，默认16比特PCM
    private AudioRecord mRecorder;
    private int bufferSize;
    private File recordingFile = new File(TFileHelper.getInstance().getRoot() + "/test/a.pcm");

    public void prepare(){
        bufferSize = AudioRecord.getMinBufferSize(sampleRate, channelConfig, audioFormat)*2;
        //        buffer=new byte[bufferSize];
        mRecorder=new AudioRecord(MediaRecorder.AudioSource.MIC,sampleRate,channelConfig,
                audioFormat,bufferSize);
    }

    public void start() throws IOException {
        byte[] tempBuffer = new byte[bufferSize];
        if (mRecorder.getState() != AudioRecord.STATE_INITIALIZED) {
            stop();
            return;
        }

        //开始录制
        mRecorder.startRecording();
        //循环读取数据到buffer中，并保存buffer中的数据到文件中
        Log.e(TAG, "start: 录音中。。。");

        TFileHelper.getInstance().deleteFile(recordingFile.getAbsolutePath());
        TFileHelper.getInstance().createFile(recordingFile.getAbsolutePath());
        FileOutputStream fileOutputStream = null;
        try {
            fileOutputStream = new FileOutputStream(recordingFile);
            int length;
            while ((length = mRecorder.read(tempBuffer, 0, bufferSize)) != -1) {
                fileOutputStream.write(tempBuffer, 0, length);
                fileOutputStream.flush();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileOutputStream != null) {
                try {
                    fileOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public void stop(){
        //中止循环并结束录制
        mRecorder.stop();
        Log.e(TAG, "start: 录音结束。。。");
    }

    //播放音频（PCM）
    public void play()
    {
        DataInputStream dis=null;
        try {
            //从音频文件中读取声音
            dis=new DataInputStream(new BufferedInputStream(new FileInputStream(recordingFile)));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        //最小缓存区
        int bufferSizeInBytes= AudioTrack.getMinBufferSize(sampleRate,AudioFormat.CHANNEL_OUT_MONO,AudioFormat.ENCODING_PCM_16BIT);
        //创建AudioTrack对象   依次传入 :流类型、采样率（与采集的要一致）、音频通道（采集是IN 播放时OUT）、量化位数、最小缓冲区、模式
        /**
         * !!注意，音频通道与录制时的音频通道要保持一致。
         */
        AudioTrack player=new AudioTrack(AudioManager.STREAM_MUSIC,sampleRate,AudioFormat.CHANNEL_OUT_STEREO,AudioFormat.ENCODING_PCM_16BIT, bufferSizeInBytes, AudioTrack.MODE_STREAM);

        byte[] data =new byte [bufferSizeInBytes];
        player.play();//开始播放
        while(true)
        {
            int i=0;
            try {
                while(dis.available()>0&&i<data.length)
                {
                    data[i]=dis.readByte();
                    i++;
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            player.write(data,0,data.length);

            if(i!=bufferSizeInBytes) //表示读取完了
            {
                player.stop();//停止播放
                player.release();//释放资源
                break;
            }
        }

    }

    public AudioRecord getmRecorder() {
        return mRecorder;
    }

    public int getBufferSize() {
        return bufferSize;
    }
}

二、缓冲区
https://blog.csdn.net/bzlj2912009596/article/details/75581675

三、音频AAC编码
关于AAC编码的文章：
https://blog.csdn.net/jay100500/article/details/52955232/ （AAC的头文件，介绍了一款工具可以查看aac文件的头文件）

     音频AAC编码实现过程
     1）开启音频录制
     2）通过MediaCodec，将音频编码，得到AAC裸流，加上AAC头，然后再写入文件。
     代码如下：

         package com.xinyi.czsuperrecorder.code.audio;

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

import com.xinyi.baselib.io.tf.TFileHelper;
import com.xinyi.czsuperrecorder.Config;

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

/**
 * Created by XinYi on 2018/7/5.
 * AAC编码
 */
public class AACEncoder {
    private static final String TAG = "AACEncoder";

    private String mime = "audio/mp4a-latm";    //录音编码的mime
    private int rate=256000;                    //编码的key bit rate
    private  MediaCodec mEnc;
    private AudioRecorder audioRecorder;
    private File recordingFile = new File(TFileHelper.getInstance().getRoot() + "/test/a.m4a");
    private boolean isStopped = true;
    private int bufferSize;

    public AACEncoder(AudioRecorder audioRecorder) {
        this.audioRecorder = audioRecorder;
        isStopped = true;
    }

    public void prepare(){
        audioRecorder.prepare();
        try {
            bufferSize = 0;
            //相对于上面的音频录制，我们需要一个编码器的实例
            MediaFormat format=MediaFormat.createAudioFormat(mime, Config.sampleRate,Config.channelCount);
            format.setInteger(MediaFormat.KEY_AAC_PROFILE, MediaCodecInfo.CodecProfileLevel.AACObjectLC);
            format.setInteger(MediaFormat.KEY_BIT_RATE, rate);
            mEnc= MediaCodec.createEncoderByType(mime);
            mEnc.configure(format,null,null,MediaCodec.CONFIGURE_FLAG_ENCODE);  //设置为编码器
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    public void start() throws IOException {
//同样，在设置录音开始的时候，也要设置编码开始
        mEnc.start();

//之前的音频录制是直接循环读取，然后写入文件，这里需要做编码处理再写入文件
//这里的处理就是和之前传送带取盒子放原料的流程一样了，注意一般在子线程中循环处理
        isStopped = false;
        MediaCodec.BufferInfo mInfo=new MediaCodec.BufferInfo();
        FileOutputStream  fos = null;
        TFileHelper.getInstance().deleteFile(recordingFile.getAbsolutePath());
        TFileHelper.getInstance().createFile(recordingFile.getAbsolutePath());

        try {
            fos = new FileOutputStream(recordingFile);
            audioRecorder.start();

            while (!isStopped){     //循环读取AudioRecorder的数据流
                int index=mEnc.dequeueInputBuffer(-1);
                Log.e(TAG, "start: index1 = " + index);
                if(index>=0){
                    final ByteBuffer buffer=mEnc.getInputBuffer(index);
                    buffer.clear();
                    int length=audioRecorder.getmRecorder().read(buffer,audioRecorder.getBufferSize());
                    Log.e(TAG, "start length = : " + length);
                    if(length>0){
                        mEnc.queueInputBuffer(index,0,length,System.nanoTime()/1000,0);
                    }
                }

                int outIndex;
                //每次取出的时候，把所有加工好的都循环取出来
                do{
                    outIndex=mEnc.dequeueOutputBuffer(mInfo,0);
                    Log.e(TAG, "start: index2 = " + outIndex);
                    if(outIndex>=0){
                        ByteBuffer buffer=mEnc.getOutputBuffer(outIndex);
                        buffer.position(mInfo.offset);
                        //AAC编码，需要加数据头，AAC编码数据头固定为7个字节
                        byte[] temp=new byte[mInfo.size+7];
                        buffer.get(temp,7,mInfo.size);
                        addADTStoPacket(temp,temp.length);
                        fos.write(temp);
                        mEnc.releaseOutputBuffer(outIndex,false);
                    }else if(outIndex ==MediaCodec.INFO_TRY_AGAIN_LATER){
                        //TODO something
                    }else if(outIndex==MediaCodec.INFO_OUTPUT_FORMAT_CHANGED){
                        //TODO something
                    }
                }while (outIndex>=0);
            }
            //编码停止，发送编码结束的标志，循环结束后，停止并释放编码器
            mEnc.stop();
            mEnc.release();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (MediaCodec.CryptoException e) {
            e.printStackTrace();
        } finally {
            if(fos != null){
                fos.close();
            }
        }
    }

    /**
     * 给编码出的aac裸流添加adts头字段
     * @param packet 要空出前7个字节，否则会搞乱数据
     * @param packetLen
     */
    private void addADTStoPacket(byte[] packet, int packetLen) {
        int profile = 2;  //AAC LC
        int freqIdx = 4;  //44.1KHz
        int chanCfg = 2;  //CPE
        packet[0] = (byte)0xFF;
        packet[1] = (byte)0xF9;
        packet[2] = (byte)(((profile-1)<<6) + (freqIdx<<2) +(chanCfg>>2));
        packet[3] = (byte)(((chanCfg&3)<<6) + (packetLen>>11));
        packet[4] = (byte)((packetLen&0x7FF) >> 3);
        packet[5] = (byte)(((packetLen&7)<<5) + 0x1F);
        packet[6] = (byte)0xFC;
    }

    public void stop(){
        audioRecorder.stop();
        isStopped = true;
    }

}