使用libavcodec解码音频，并使用libAO播放

Question

我使用以下代码片段来解码音频文件（用MP3、WAV、WMV测试）。

但当它播放音频时，它只是发出静态声音，并不时崩溃。有没有迹象表明我做错了什么？

#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,"%sn",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 %dn",packet.size,len);
                ao_play(adevice, (char*)frame->data, len);
            }
        }

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

Answer 1

好的，这里有一个工作代码示例：

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("U8n");
        sformat.bits=8;
    }else if(sfmt==AV_SAMPLE_FMT_S16){
        printf("S16n");
        sformat.bits=16;
    }else if(sfmt==AV_SAMPLE_FMT_S32){
        printf("S32n");
        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 Finishedn");
            }
        }else {
            printf("Someother packet possibly Videon");
        }

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