使用FFMpeg解碼音頻通過Android

Question

我可以使用下面的代碼播放Wav文件沒有問題。當試圖播放Mp3格式的完全相同的媒體時，我只會看到亂碼。我相信我從根本上誤解了avcodec_decode_audio3函數的工作原理。

由於Wav文件在解碼時包含PCM數據，因此可以直接進入AudioTrack.write函數。必須有一些額外的步驟才能讓Mp3s像這樣工作。我不知道我錯過了什麼，但是我現在一直在拉我的頭髮一週。

Java代碼的

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代碼

#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; 
    } 

要添加一些細節。當調用帶有一個WAV文件這個功能我得到以下日誌數據

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 

當MP3文件，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

我能夠通過在ffmpeg源碼的libavcodec中找到api_example.c文件中的audio_decode_example代碼來解決我的問題，並對其進行修改以滿足我的需求。以下是代碼。需要注意的是，它不會動態選擇正確的解碼器進行解碼，這是我將不得不與其他一些項目一起解決的問題。 Java代碼保持不變。

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 decoding\n"); 

     /* find the mpeg audio decoder */ 
     codec = avcodec_find_decoder(CODEC_ID_MP3); 
     if (!codec) { 
      fprintf(stderr, "codec not found\n"); 
      exit(1); 
     } 

     c= avcodec_alloc_context(); 

     /* open it */ 
     if (avcodec_open(c, codec) < 0) { 
      fprintf(stderr, "could not open codec\n"); 
      exit(1); 
     } 

     outbuf = malloc(AVCODEC_MAX_AUDIO_FRAME_SIZE); 

     f = fopen(filename, "rb"); 
     if (!f) { 
      fprintf(stderr, "could not open %s\n", 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 decoding\n"); 
       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

啊叫，你可能需要後檢查data_size值調用avcodec_decode_audio3：現在您總是將返回值提供給play方法，但如果data_size小於0，那麼它不是有效的幀解碼。