使用FFMpeg通过Android解码音频

Question

我可以使用以下代码播放Wav文件而不会出现问题。当我尝试以Mp3格式播放完全相同的媒体时，我只会收到垃圾。我相信我从根本上误解了avcodec_decode_audio3函数的工作原理。

由于Wav文件在解码时包含PCM数据，因此可以直接进入AudioTrack.write功能。必须有一些额外的步骤才能让MP3像这样工作。我不知道我错过了什么，但我已经拔头发一个星期了。

Java代码

package com.rohaupt.RRD2;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import android.app.Activity;
import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioTrack;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.SystemClock;
public class player extends Activity
{
    private AudioTrack track;
    private FileOutputStream os;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        createEngine();
        MediaPlayer mp = new MediaPlayer();
        mp.start();
        int bufSize = AudioTrack.getMinBufferSize(32000,
                                                  AudioFormat.CHANNEL_CONFIGURATION_STEREO, 
                                                  AudioFormat.ENCODING_PCM_16BIT);

        track = new AudioTrack(AudioManager.STREAM_MUSIC, 
                               32000, 
                               AudioFormat.CHANNEL_CONFIGURATION_STEREO, 
                               AudioFormat.ENCODING_PCM_16BIT, 
                               bufSize,
                               AudioTrack.MODE_STREAM);
        byte[] bytes = new byte[bufSize];
        try {
            os = new FileOutputStream("/sdcard/a.out",false);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        String result = loadFile("/sdcard/a.mp3",bytes);
        try {
            os.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    void playSound(byte[] buf, int size) {  
        //android.util.Log.v("ROHAUPT", "RAH Playing");
        if(track.getPlayState()!=AudioTrack.PLAYSTATE_PLAYING)
            track.play();
        track.write(buf, 0, size);
        try {
            os.write(buf,0,size);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    private native void createEngine();
    private native String loadFile(String file, byte[] array);
    /** Load jni .so on initialization*/ 
    static {
         System.loadLibrary("avutil"); 
         System.loadLibrary("avcore"); 
         System.loadLibrary("avcodec");
         System.loadLibrary("avformat");
         System.loadLibrary("avdevice");
         System.loadLibrary("swscale");
         System.loadLibrary("avfilter");
         System.loadLibrary("ffmpeg");
    }
}

C代码

#include <assert.h>
#include <jni.h>
#include <string.h>
#include <android/log.h>
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#define DEBUG_TAG "ROHAUPT"  
void Java_com_rohaupt_RRD2_player_createEngine(JNIEnv* env, jclass clazz)
    {
        avcodec_init();
        av_register_all();

    }
    jstring Java_com_rohaupt_RRD2_player_loadFile(JNIEnv* env, jobject obj,jstring file,jbyteArray array)
    {   
        jboolean            isCopy;  
        int                 i;
        int                 audioStream=-1;
        int                 res;
        int                 decoded = 0;
        int                 out_size;
        AVFormatContext     *pFormatCtx;
        AVCodecContext      *aCodecCtx;
        AVCodecContext      *c= NULL;
        AVCodec             *aCodec;
        AVPacket            packet;
        jclass              cls = (*env)->GetObjectClass(env, obj);
        jmethodID           play = (*env)->GetMethodID(env, cls, "playSound", "([BI)V");//At the begining of your main function
        const char *        szfile = (*env)->GetStringUTFChars(env, file, &isCopy);
        int16_t *           pAudioBuffer = (int16_t *) av_malloc (AVCODEC_MAX_AUDIO_FRAME_SIZE*2+FF_INPUT_BUFFER_PADDING_SIZE);
        int16_t *           outBuffer = (int16_t *) av_malloc (AVCODEC_MAX_AUDIO_FRAME_SIZE*2+FF_INPUT_BUFFER_PADDING_SIZE);

        __android_log_print(ANDROID_LOG_INFO, DEBUG_TAG, "RAH28 Starting");
        res = av_open_input_file(&pFormatCtx, szfile, NULL, 0, NULL);
        if(res!=0)
        {
            __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH opening input failed with result: [%d]", res);
            return file;
        }
        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH getting stream info");
        res = av_find_stream_info(pFormatCtx);
        if(res<0)
        {
            __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH getting stream info failed with result: [%d]", res);
            return file;
        }
        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH getting audio stream");
        for(i=0; i < pFormatCtx->nb_streams; i++) {
          if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO &&
             audioStream < 0) {
            audioStream=i;
          }
        }

        if(audioStream==-1)
        {
            __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH couldn't find audio stream");
            return file;
        }
        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH audio stream found with result: [%d]", res);

        aCodecCtx=pFormatCtx->streams[audioStream]->codec;
        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH audio codec info loaded");
        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH audio codec info [%d]", aCodecCtx->codec_id);
        aCodec = avcodec_find_decoder(aCodecCtx->codec_id);
        if(!aCodec) {
           __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH audio codec unsupported");
           return file;
        }
        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH audio codec info found");

        res = avcodec_open(aCodecCtx, aCodec);
        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH audio codec loaded [%d] [%d]",aCodecCtx->sample_fmt,res);
        //c=avcodec_alloc_context();
        av_init_packet(&packet);

        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH channels [%d] sample rate [%d] sample format [%d]",aCodecCtx->channels,aCodecCtx->sample_rate,aCodecCtx->sample_fmt);

        int x,y;
        x=0;y=0;
        while (av_read_frame(pFormatCtx, &packet)>= 0) {
            __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH frame read: [%d] [%d]",x++,y);
            if (aCodecCtx->codec_type == AVMEDIA_TYPE_AUDIO) {
                        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH audio ready");
                        int data_size = AVCODEC_MAX_AUDIO_FRAME_SIZE*2+FF_INPUT_BUFFER_PADDING_SIZE;
                        int size=packet.size;
                        y=0;
                        decoded = 0;
                        __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH packet size: [%d]", size);
                        while(size > 0) {
                                __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH decoding: [%d] [%d]",x,y++);
                                int len = avcodec_decode_audio3(aCodecCtx, pAudioBuffer, &data_size, &packet);

                                __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH 1 size [%d] len [%d] data_size [%d] out_size [%d]",size,len,data_size,out_size);
                                jbyte *bytes = (*env)->GetByteArrayElements(env, array, NULL);
                                memcpy(bytes + decoded, pAudioBuffer, len); //

                                __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH 2");
                                (*env)->ReleaseByteArrayElements(env, array, bytes, 0);
                                __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH 3");
                                (*env)->CallVoidMethod(env, obj, play, array, len);
                                __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH 4");

                                size -= len;
                                decoded += len;
                       }
                       av_free_packet(&packet);
            }
     }
          // Close the video file
        av_close_input_file(pFormatCtx);
        //__android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "RAH Finished Running result: [%d]", res);
        (*env)->ReleaseStringUTFChars(env, file, szfile);   
        return file;  
    }

添加一些细节。当用Wav文件调用此函数时，我得到以下日志数据

I/ROHAUPT (  227): RAH28 Starting
D/ROHAUPT (  227): RAH getting stream info
D/ROHAUPT (  227): RAH getting audio stream
D/ROHAUPT (  227): RAH audio stream found with result: [0]
D/ROHAUPT (  227): RAH audio codec info loaded
D/ROHAUPT (  227): RAH audio codec info [65536]
D/ROHAUPT (  227): RAH audio codec info found
D/ROHAUPT (  227): RAH audio codec loaded [1] [0]
D/ROHAUPT (  227): RAH channels [2] sample rate [32000] sample format [1]
D/ROHAUPT (  227): RAH frame read: [0] [0]
D/ROHAUPT (  227): RAH audio ready
D/ROHAUPT (  227): RAH packet size: [4096]
D/ROHAUPT (  227): RAH decoding: [1] [0]
D/ROHAUPT (  227): RAH 1 size [4096] len [4096] data_size [4096] out_size [0]
D/ROHAUPT (  227): RAH 2
D/ROHAUPT (  227): RAH 3
D/ROHAUPT (  227): RAH 4
D/ROHAUPT (  227): RAH frame read: [1] [1]
D/ROHAUPT (  227): RAH audio ready
...
D/ROHAUPT (  227): RAH frame read: [924] [1]
D/ROHAUPT (  227): RAH audio ready
D/ROHAUPT (  227): RAH packet size: [4096]
D/ROHAUPT (  227): RAH decoding: [925] [0]
D/ROHAUPT (  227): RAH 1 size [4096] len [4096] data_size [4096] out_size [0]
D/ROHAUPT (  227): RAH 2
D/ROHAUPT (  227): RAH 3
D/ROHAUPT (  227): RAH 4
D/ROHAUPT (  227): RAH frame read: [925] [1]
D/ROHAUPT (  227): RAH audio ready
D/ROHAUPT (  227): RAH packet size: [3584]
D/ROHAUPT (  227): RAH decoding: [926] [0]
D/ROHAUPT (  227): RAH 1 size [3584] len [3584] data_size [3584] out_size [0]
D/ROHAUPT (  227): RAH 2
D/ROHAUPT (  227): RAH 3
D/ROHAUPT (  227): RAH 4

当用Mp3文件调用时，我得到以下

I/ROHAUPT (  280): RAH28 Starting
D/ROHAUPT (  280): RAH getting stream info
D/ROHAUPT (  280): RAH getting audio stream
D/ROHAUPT (  280): RAH audio stream found with result: [0]
D/ROHAUPT (  280): RAH audio codec info loaded
D/ROHAUPT (  280): RAH audio codec info [86017]
D/ROHAUPT (  280): RAH audio codec info found
D/ROHAUPT (  280): RAH audio codec loaded [1] [0]
D/ROHAUPT (  280): RAH channels [2] sample rate [32000] sample format [1]
D/ROHAUPT (  280): RAH frame read: [0] [0]
D/ROHAUPT (  280): RAH audio ready
D/ROHAUPT (  280): RAH packet size: [432]
D/ROHAUPT (  280): RAH decoding: [1] [0]
D/ROHAUPT (  280): RAH 1 size [432] len [432] data_size [4608] out_size [0]
D/ROHAUPT (  280): RAH 2
...
D/ROHAUPT (  280): RAH frame read: [822] [1]
D/ROHAUPT (  280): RAH audio ready
D/ROHAUPT (  280): RAH packet size: [432]
D/ROHAUPT (  280): RAH decoding: [823] [0]
D/ROHAUPT (  280): RAH 1 size [432] len [432] data_size [4608] out_size [0]
D/ROHAUPT (  280): RAH 2
D/ROHAUPT (  280): RAH 3
D/ROHAUPT (  280): RAH 4
D/ROHAUPT (  280): RAH frame read: [823] [1]
D/ROHAUPT (  280): RAH audio ready
D/ROHAUPT (  280): RAH packet size: [432]
D/ROHAUPT (  280): RAH decoding: [824] [0]
D/ROHAUPT (  280): RAH 1 size [432] len [432] data_size [4608] out_size [0]
D/ROHAUPT (  280): RAH 2
D/ROHAUPT (  280): RAH 3
D/ROHAUPT (  280): RAH 4

Answer 1

我能够通过使用在ffmpeg源代码的libavcodec中的api_example.c文件中找到的audio_decode_example代码来解决我的问题，并对其进行修改以满足我的需求。下面是代码。需要注意的是，它并没有动态地选择正确的编解码器进行解码，这是我接下来必须解决的问题，还有一些其他项目。java代码保持不变。

void Java_com_rohaupt_RRD2_player_Example(JNIEnv* env, jobject obj,jstring file,jbyteArray array)
    {
        jboolean            isfilenameCopy;
        const char *        filename = (*env)->GetStringUTFChars(env, file, &isfilenameCopy);
        AVCodec *codec;
        AVCodecContext *c= NULL;
        int out_size, len;
        FILE *f, *outfile;
        uint8_t *outbuf;
        uint8_t inbuf[AUDIO_INBUF_SIZE + FF_INPUT_BUFFER_PADDING_SIZE];
        AVPacket avpkt;
        jclass              cls = (*env)->GetObjectClass(env, obj);
        jmethodID           play = (*env)->GetMethodID(env, cls, "playSound", "([BI)V");//At the begining of your main function
        av_init_packet(&avpkt);
        printf("Audio decodingn");
        /* find the mpeg audio decoder */
        codec = avcodec_find_decoder(CODEC_ID_MP3);
        if (!codec) {
            fprintf(stderr, "codec not foundn");
            exit(1);
        }
        c= avcodec_alloc_context();
        /* open it */
        if (avcodec_open(c, codec) < 0) {
            fprintf(stderr, "could not open codecn");
            exit(1);
        }
        outbuf = malloc(AVCODEC_MAX_AUDIO_FRAME_SIZE);
        f = fopen(filename, "rb");
        if (!f) {
            fprintf(stderr, "could not open %sn", filename);
            exit(1);
        }
        /* decode until eof */
        avpkt.data = inbuf;
        avpkt.size = fread(inbuf, 1, AUDIO_INBUF_SIZE, f);
        while (avpkt.size > 0) {
            out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;
            len = avcodec_decode_audio3(c, (short *)outbuf, &out_size, &avpkt);
            if (len < 0) {
                fprintf(stderr, "Error while decodingn");
                exit(1);
            }
            if (out_size > 0) {
                /* if a frame has been decoded, output it */
                jbyte *bytes = (*env)->GetByteArrayElements(env, array, NULL);
                memcpy(bytes, outbuf, out_size); //
                (*env)->ReleaseByteArrayElements(env, array, bytes, 0);
                (*env)->CallVoidMethod(env, obj, play, array, out_size);
            }
            avpkt.size -= len;
            avpkt.data += len;
            if (avpkt.size < AUDIO_REFILL_THRESH) {
                /* Refill the input buffer, to avoid trying to decode
                 * incomplete frames. Instead of this, one could also use
                 * a parser, or use a proper container format through
                 * libavformat. */
                memmove(inbuf, avpkt.data, avpkt.size);
                avpkt.data = inbuf;
                len = fread(avpkt.data + avpkt.size, 1,
                            AUDIO_INBUF_SIZE - avpkt.size, f);
                if (len > 0)
                    avpkt.size += len;
            }
        }
        fclose(f);
        free(outbuf);
        avcodec_close(c);
        av_free(c);
    }

Answer 2

Ah，您可能需要在调用avcodec_decode_audio3之后检查data_size值：现在您总是将返回值提供给play方法，但如果data_size小于0，则它不是有效的帧解码。