【HarmonyOS】实现将pcm音频文件进行编码并写入文件（API6 Java）

 【关键字】

音频编码、管道模式、createEncoder

【写在前面】

在使用API6开发HarmonyOS应用时，如何将pcm源文件进行编码并写入文件，最后生成aac文件，本文直接附上主要代码开发步骤供大家参考。

【主要功能代码】

import ohos.media.codec.Codec;
import ohos.media.common.BufferInfo;
import ohos.media.common.Format;
import ohos.media.common.Source;

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

public class AudioEncoder {

    void creatEncoder(){

    }

    FileOutputStream fileOutputStream = null;

    public void encode(){
        System.out.println("encode start");
        try {
            File fd = new File("/data/data/com.example.myapplication/11.aac");
            fileOutputStream = new FileOutputStream(fd, true);
        } catch (FileNotFoundException e) {
            System.out.println("FileNotFoundException");
        } finally {
        }
        final Codec encoder = Codec.createEncoder();
        String path = "/data/data/com.example.myapplication/11.pcm";
        System.out.println("encoder = " + encoder);
        boolean ret = encoder.setSource(new Source(path), null);
        System.out.println("setSource ret = " + ret);
		
        Format fmt = new Format();
	// format格式中转码率和声道需与pcm相同
        fmt.putStringValue(Format.MIME, Format.AUDIO_AAC);
        fmt.putIntValue(Format.BIT_RATE, 128000);
        fmt.putIntValue(Format.CHANNEL, 2);
        fmt.putIntValue(Format.SAMPLE_RATE, 44100);
        fmt.putIntValue(Format.FRAME_RATE, 30); // 此设置必须，数值一般为30/60，或自行设置需要数值

        boolean b1 = encoder.setSourceFormat(fmt);
        System.out.println("setSourceFormat = " + b1);
        Codec.ICodecListener listener = new Codec.ICodecListener() {
            @Override
            public void onReadBuffer(ByteBuffer byteBuffer, BufferInfo bufferInfo, int trackId) {
                System.out.println("byteBuffer = " + byteBuffer + "trackId = " + trackId + "bufferinfo = " + bufferInfo.bufferType);
                if(bufferInfo.bufferType == 4){
                    encoder.stop();
                    encoder.release();
                    try {
                        fileOutputStream.close();
                    } catch (IOException e) {
			// 打印异常
                        System.out.println("IOException");
                    }
                    return;
                }
                writeFile(byteBuffer,bufferInfo,trackId);

            }
            @Override
            public void one rror(int errorCode, int act, int trackId) {
                System.out.println( "PlayerCallback one rror errorCode: "+errorCode +", trackId:"+trackId);
            }
        };
        boolean b = encoder.registerCodecListener(listener);
        System.out.println("registerCodecListener = " + b);

        boolean start = encoder.start();
        System.out.println("start = " + start);
    }


    private void writeFile(ByteBuffer outputBuffer, BufferInfo info, int trackId) {
        try {
            final byte[] chunk = new byte[info.size+7];
            addADTSHeader(chunk,info.size+7);
            outputBuffer.get(chunk,7,info.size);
            fileOutputStream.write(chunk);
            outputBuffer.clear();
        } catch (FileNotFoundException e) {
            System.out.println("FileNotFoundException");
        } catch (IOException e) {
            System.out.println("IOException");
        } finally {
		
        }
    }
    /**
     * 添加AAC帧文件头
     *
     * @param packet    packet
     * @param packetLen packetLen
     */
    private void addADTSHeader(byte[] packet, int packetLen) {
        int profile = 2; // AAC
        int freqIdx = 4; // 44.1kHz
        int channelCount = 2;//声道
        packet[0] = (byte) 0xFF;
        packet[1] = (byte) 0xF9;
        packet[2] = (byte) (((profile - 1) << 6) + (freqIdx << 2) + (channelCount >> 2));
        packet[3] = (byte) (((channelCount & 3) << 6) + (packetLen >> 11));
        packet[4] = (byte) ((packetLen & 0x7FF) >> 3);
        packet[5] = (byte) (((packetLen & 7) << 5) + 0x1F);
        packet[6] = (byte) 0xFC;
    }
}

【说明和注意事项】

1、AAC文件有两种添加头文件方式：ADIF与ADTS，此处使用ADTS方式，ADTS是每一段编码都有一个头部，因此并不能只添加一次，需要在回调中添加头文件；添加头文件保存的aac文件可以直接播放；

2、format中需要设置FRAME_RATE，即fmt.putIntValue(Format.FRAME_RATE, 30);，数值必须大于0，否则可能会编码失败

3、编解码功能建议在子线程中执行，不要在主线程中。

【参考文档】

视频编解码文档：https://developer.harmonyos.com/cn/docs/documentation/doc-guides/media-video-codec-0000000000031749