Giải mã âm thanh bằng cách sử dụng libavcodec và phát bằng libAO?

Question

Tôi sử dụng đoạn mã sau để giải mã các tệp âm thanh (được thử nghiệm bằng MP3, WAV, WMV).

Nhưng khi phát âm thanh, nó chỉ phát ra âm thanh tĩnh và treo theo thời gian. Bất kỳ gợi ý nào về những gì tôi đang làm sai ở đây?

#include <stdlib.h> 
#include <stdio.h> 
#include <string.h> 
#include <math.h> 


extern "C" { 
#include "libavutil/mathematics.h" 
#include "libavformat/avformat.h" 
#include "libswscale/swscale.h" 
#include <ao/ao.h> 

} 

void die(const char *msg) 
{ 
    fprintf(stderr,"%s\n",msg); 
    exit(1); 
} 

int main(int argc, char **argv) 
{ 

    const char* input_filename=argv[1]; 

    //avcodec_register_all(); 
    av_register_all(); 
    //av_ini 

    AVFormatContext* container=avformat_alloc_context(); 
    if(avformat_open_input(&container,input_filename,NULL,NULL)<0){ 
     die("Could not open file"); 
    } 

    if(av_find_stream_info(container)<0){ 
     die("Could not find file info"); 
    } 
    av_dump_format(container,0,input_filename,false); 

    int stream_id=-1; 
    int i; 
    for(i=0;i<container->nb_streams;i++){ 
     if(container->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO){ 
      stream_id=i; 
      break; 
     } 
    } 
    if(stream_id==-1){ 
     die("Could not find Audio Stream"); 
    } 

    AVDictionary *metadata=container->metadata; 

    AVCodecContext *ctx=container->streams[stream_id]->codec; 
    AVCodec *codec=avcodec_find_decoder(ctx->codec_id); 

    if(codec==NULL){ 
     die("cannot find codec!"); 
    } 

    if(avcodec_open(ctx,codec)<0){ 
     die("Codec cannot be found"); 
    } 

    //ctx=avcodec_alloc_context3(codec); 

    //initialize AO lib 
    ao_initialize(); 

    int driver=ao_default_driver_id(); 

    ao_sample_format sformat; 
    sformat.bits=16; 
    sformat.channels=2; 
    sformat.rate=44100; 
    sformat.byte_format=AO_FMT_NATIVE; 
    sformat.matrix=0; 

    ao_device *adevice=ao_open_live(driver,&sformat,NULL); 
    //end of init AO LIB 

    AVPacket packet; 
    av_init_packet(&packet); 

    AVFrame *frame=avcodec_alloc_frame(); 

    int buffer_size=AVCODEC_MAX_AUDIO_FRAME_SIZE; 
    uint8_t buffer[buffer_size]; 
    packet.data=buffer; 
    packet.size =buffer_size; 



    int len; 
    int frameFinished=0; 
    while(av_read_frame(container,&packet)>=0) 
    { 

     if(packet.stream_index==stream_id){ 
      //printf("Audio Frame read \n"); 
      int len=avcodec_decode_audio4(ctx,frame,&frameFinished,&packet); 
      //frame-> 
      if(frameFinished){ 
       //printf("Finished reading Frame %d %d\n",packet.size,len); 
       ao_play(adevice, (char*)frame->data, len); 
      } 

     } 


    } 

    av_close_input_file(container); 
    ao_shutdown(); 
    return 0; 
} 

Answer 1

Ok, đây là một mẫu mã làm việc:

int main(int argc, char **argv) 
{ 

    const char* input_filename=argv[1]; 

    //avcodec_register_all(); 
    av_register_all(); 
    //av_ini 

    AVFormatContext* container=avformat_alloc_context(); 
    if(avformat_open_input(&container,input_filename,NULL,NULL)<0){ 
     die("Could not open file"); 
    } 

    if(av_find_stream_info(container)<0){ 
     die("Could not find file info"); 
    } 
    av_dump_format(container,0,input_filename,false); 

    int stream_id=-1; 
    int i; 
    for(i=0;i<container->nb_streams;i++){ 
     if(container->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO){ 
      stream_id=i; 
      break; 
     } 
    } 
    if(stream_id==-1){ 
     die("Could not find Audio Stream"); 
    } 

    AVDictionary *metadata=container->metadata; 

    AVCodecContext *ctx=container->streams[stream_id]->codec; 
    AVCodec *codec=avcodec_find_decoder(ctx->codec_id); 

    if(codec==NULL){ 
     die("cannot find codec!"); 
    } 

    if(avcodec_open(ctx,codec)<0){ 
     die("Codec cannot be found"); 
    } 

    //ctx=avcodec_alloc_context3(codec); 

    //initialize AO lib 
    ao_initialize(); 

    int driver=ao_default_driver_id(); 

    ao_sample_format sformat; 
    AVSampleFormat sfmt=ctx->sample_fmt; 
    if(sfmt==AV_SAMPLE_FMT_U8){ 
     printf("U8\n"); 

     sformat.bits=8; 
    }else if(sfmt==AV_SAMPLE_FMT_S16){ 
     printf("S16\n"); 
     sformat.bits=16; 
    }else if(sfmt==AV_SAMPLE_FMT_S32){ 
     printf("S32\n"); 
     sformat.bits=32; 
    } 

    sformat.channels=ctx->channels; 
    sformat.rate=ctx->sample_rate; 
    sformat.byte_format=AO_FMT_NATIVE; 
    sformat.matrix=0; 

    ao_device *adevice=ao_open_live(driver,&sformat,NULL); 
    //end of init AO LIB 

    AVPacket packet; 
    av_init_packet(&packet); 

    AVFrame *frame=avcodec_alloc_frame(); 



    int buffer_size=AVCODEC_MAX_AUDIO_FRAME_SIZE+ FF_INPUT_BUFFER_PADDING_SIZE;; 
    uint8_t buffer[buffer_size]; 
    packet.data=buffer; 
    packet.size =buffer_size; 



    int len; 
    int frameFinished=0; 
    while(av_read_frame(container,&packet)>=0) 
    { 

     if(packet.stream_index==stream_id){ 
      //printf("Audio Frame read \n"); 
      int len=avcodec_decode_audio4(ctx,frame,&frameFinished,&packet); 
      //frame-> 
      if(frameFinished){ 
       //printf("Finished reading Frame len : %d , nb_samples:%d buffer_size:%d line size: %d \n",len,frame->nb_samples,buffer_size,frame->linesize[0]); 
       ao_play(adevice, (char*)frame->extended_data[0],frame->linesize[0]); 
      }else{ 
       //printf("Not Finished\n"); 
      } 

     }else { 
      printf("Someother packet possibly Video\n"); 
     } 


    } 

    av_close_input_file(container); 
    ao_shutdown(); 
    return 0; 
}