使用FFmpeg库抽取视频中的音频数据

- (IBAction)extraAudioAction:(id)sender {
    
    //需要处理的视频文件路径
    NSString * path = [[NSBundle mainBundle] pathForResource:@"test" ofType:@"mp4"];
    char  srcChar [ 1024 ];
    strcpy (srcChar ,( char  *)[path  UTF8String]);
    // 处理好的文件存储路径
    NSString * dstpath = [NSString stringWithFormat:@"%@/Library/Caches/1-1.aac",NSHomeDirectory()];
    char  dstChar [ 1024 ];
    strcpy (dstChar ,( char  *)[dstpath  UTF8String]);

    char * argv[2];
    argv[0] = srcChar;
    argv[1] = dstChar;
    
    NSLog(@"存储路径：%@", dstpath);
    
    extraAudio(2, argv);
}

#pragma mark 音频抽取 aac
void extraAudio(int argc, char* argv[]) {
    
    int ret = -1;
    int idx = -1;
    
    // 1、处理一些参数
    char* src;
    char* dst;

    av_log_set_level(AV_LOG_DEBUG);
    if (argc < 2)
    {
        av_log(NULL, AV_LOG_INFO, "arguments must be more than 2!\n");
        exit(-1);
    }

    src = argv[0];
    dst = argv[1];
    
    AVFormatContext *pFmtCtx = NULL;
    AVFormatContext *oFmtCtx = NULL;

    const AVOutputFormat *outFmt = NULL;
    AVStream *outStream = NULL;
    AVStream *inStream = NULL;

    AVPacket pkt;

    // 2、打开多媒体文件
    if((ret = avformat_open_input(&pFmtCtx, src, NULL, NULL)) < 0)
    {
        av_log(NULL, AV_LOG_ERROR, "%s\n", av_err2str(ret));
        exit(-1);
    }

    // 3、从多媒体文件中找到音频流
    idx = av_find_best_stream(pFmtCtx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);
    if(idx < 0) {
        av_log(pFmtCtx, AV_LOG_ERROR, "Does not include audio stream!\n");
        goto _ERROR;
    }

    // 4、打开目的文件的上下文
    oFmtCtx = avformat_alloc_context();
    if(!oFmtCtx){
        av_log(NULL, AV_LOG_ERROR, "NO Memory!\n");
        goto _ERROR;
    }
    outFmt = av_guess_format(NULL, dst, NULL);
    oFmtCtx->oformat = outFmt;

    // 5、为目的文件创建一个新的音频流
    outStream = avformat_new_stream(oFmtCtx, NULL);

    // 6、设置输出音频参数
    inStream = pFmtCtx->streams[idx];
    avcodec_parameters_copy(outStream->codecpar, inStream->codecpar);
    outStream->codecpar->codec_tag = 0;

    //绑定
    ret = avio_open2(&oFmtCtx->pb, dst, AVIO_FLAG_WRITE, NULL, NULL);
    if(ret < 0 )
    {
        av_log(oFmtCtx, AV_LOG_ERROR, "%s", av_err2str(ret));
        goto _ERROR;
    }

    // 7、写多媒体文件头到目的文件
    ret = avformat_write_header(oFmtCtx, NULL);
    if(ret < 0 ){
        av_log(oFmtCtx, AV_LOG_ERROR, "%s", av_err2str(ret));
        goto _ERROR;
    }

    // 8、从源多媒体文件中读取音频数据到目的文件中
    while(av_read_frame(pFmtCtx, &pkt) >= 0) {
        if(pkt.stream_index == idx) {
            pkt.pts = av_rescale_q_rnd(pkt.pts, inStream->time_base, outStream->time_base, (AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
            pkt.dts = pkt.pts;
            pkt.duration = av_rescale_q(pkt.duration, inStream->time_base, outStream->time_base);
            pkt.stream_index = 0;
            pkt.pos = -1;
            av_interleaved_write_frame(oFmtCtx, &pkt);
            av_packet_unref(&pkt);
        }
    }

    // 9、写多媒体文件尾到文件中
    av_write_trailer(oFmtCtx);

    // 10、将申请的资源释放掉
_ERROR:
    if(pFmtCtx)
    {
        avformat_close_input(&pFmtCtx);
        pFmtCtx = NULL;
    }
    if(oFmtCtx->pb)
    {
        avio_close(oFmtCtx->pb);
    }

    if(oFmtCtx)
    {
        avformat_free_context(oFmtCtx);
        oFmtCtx = NULL;
    }
}