FFmpeg 获取视频文件中的音视频源数据

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#define AUDIO_AAC_ADTS_LEN  7
#define FILE_PATH_LENGTH    64

int set_acc_adts_header(uint8_t *header, int packet_len)
{
    int profile = 2;  //AAC LC，MediaCodecInfo.CodecProfileLevel.AACObjectLC;
    int freqIdx = 4;  //32K, 见后面注释avpriv_mpeg4audio_sample_rates中32000对应的数组下标，来自ffmpeg源码
    int chanCfg = 2;  //见后面注释channel_configuration，Stero双声道立体声

    /*int avpriv_mpeg4audio_sample_rates[] = {
    96000, 88200, 64000, 48000, 44100, 32000,
    24000, 22050, 16000, 12000, 11025, 8000, 7350
    };
    channel_configuration: 表示声道数chanCfg
    0: Defined in AOT Specifc Config
    1: 1 channel: front-center
    2: 2 channels: front-left, front-right
    3: 3 channels: front-center, front-left, front-right
    4: 4 channels: front-center, front-left, front-right, back-center
    5: 5 channels: front-center, front-left, front-right, back-left, back-right
    6: 6 channels: front-center, front-left, front-right, back-left, back-right, LFE-channel
    7: 8 channels: front-center, front-left, front-right, side-left, side-right, back-left, back-right, LFE-channel
    8-15: Reserved
    */

    //Fill in ADTS data
    header[0] = (uint8_t)0xFF;
    header[1] = (uint8_t)0xF1;
    header[2] = (uint8_t)(((profile - 1) << 6) + (freqIdx << 2) + (chanCfg >> 2));
    header[3] = (uint8_t)(((chanCfg & 3) << 6) + (packet_len >> 11));
    header[4] = (uint8_t)((packet_len & 0x7FF) >> 3);
    header[5] = (uint8_t)(((packet_len & 7) << 5) + 0x1F);
    header[6] = (uint8_t)0xFC;

    return 0;
}


int main()
{
    AVFormatContext*                format_context_p = NULL;	//ffmpeg文件管理器
    AVPacket                        pkt;
    AVCodecContext*                 codec_context_p = NULL;
    AVBitStreamFilterContext*       bit_stream_filter_p = NULL;
    int                             read_ret = 0;
    int                             video_index = -1;
    int                             audio_index = -1;
    int                             err_no;
    int                             ff_ret;
    char                            address[FILE_PATH_LENGTH] = "D://TEST.mp4"
    char                            adts_head[AUDIO_AAC_ADTS_LEN]
    unsigned char*                  begin_p = NULL;



    av_register_all();

    //打开文件
    err_no = avformat_open_input(&format_context_p, address, 0, 0);
    if (err_no < 0) {
        printf("avformat_open_input() error [%d].\n", err_no);
        return -1;
    }

    //找到流信息
    err_no = avformat_find_stream_info(format_context_p, 0);
    if (err_no < 0) {
        printf("avformat_find_stream_info() error [%d].\n", err_no);
        return -1;
    }

    av_dump_format(format_context_p, 0, format_context_p->filename, 0);

    //获取视频索引
    for (unsigned int i = 0; i < format_context_p->nb_streams; i++) {

        if (format_context_p->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_index = i;
            break;
        }
    }

    //获取音频索引
    for (unsigned int i = 0; i < format_context_p->nb_streams; i++) {

        if (format_context_p->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
            audio_index = i;
            break;
        }
    }

    //获取音频编码
    if (audio_index == -1 && video_index == -1) {
        printf("%s\n", "can not find audio or video codec index error.");
        return -1;
    }

    if (video_index >= 0) {
        //mp4中read出来的帧数据并非标准的H264 nal数据，需要filter过滤
        bit_stream_filter_p = av_bitstream_filter_init("h264_mp4toannexb");
        if (!bit_stream_filter_p) {
            printf("%s\n", "av_bitstream_filter_init() error");
            return -1;
        }
    }
    
    //初始化pkt
    av_init_packet(&pkt);
    //读取帧数据
    while(1) {      
        read_ret = av_read_frame(format_context_p, &pkt);    
        if (read_ret == AVERROR_EOF) {
            /* 
             说明：格式为mp4、avi等封装格式可以使用seek接口定位到指定位置
             但如果是一个H264等源码流的文件无法使用，需要重新初始化format_context
             */
             
            //如果起始时间戳可用
            if (format_context_p->streams[video_index]->start_time >= 0) {
                read_ret = av_seek_frame(format_context_p, video_index, format_context_p->streams[video_index]->start_time, 0);
                if (read_ret >= 0) {
                    continue;
                }
            } else {
                break;
            }
        }

        if (read_ret < 0) {
            printf("av_read_frame() error [%d].", read_ret);
            break;
        }
        
        if (pkt.stream_index == video_index) {
            //视频流
            codec_context_p = format_context_p->streams[video_index]->codec;
            /*
             说明：av_bitstream_filter_filter()函数,根据返回值判断资源的回收
             返回值 = 0，没有开辟新的内存空间，pkt.data仍然指向pkt.buf->data
             返回值 > 0, 重新开辟了新的内存空间，pkt.data为指针，pkt.size为长度
             返回值 < 0, 这种情况可能需要放弃掉该帧数据
             */
            ff_ret = av_bitstream_filter_filter(bit_stream_filter_p, codec_context_p, NULL, &pkt.data, &pkt.size, pkt.data, pkt.size, 0);
            if (ff_ret >= 0) {
                begin_p = pkt.data;
                rd_len = pkt.size;
            }

            //视频帧数据以及长度，保存文件后可以使用H264VISTA查看帧数据的正确性
            begin_p;
            rd_len;

            //分配了新的pkt->data空间,使用后销毁
            if (ff_ret > 0 && pkt.size > 0){
                av_free(pkt.data);
            }
        } else if (pkt.stream_index == audio_index) {
            //音频流
            /*
             说明：当音频编码格式为AAC时，是缺少ADTS头信息的，
             创建ADTS头
             */          
            if (format_context_p->streams[audio_index]->codec->codec_id == AV_CODEC_ID_AAC) {
                set_acc_adts_header(adts_head, pkt.size + CSS_MEDIA_CHANNEL_MEDIA_AUDIO_AAC_ATDS_LEN);

                //拼装音频数据ADTS+pkt.data
            } else {
                //音频数据，保存文件后使用播放器播放
            }

        }
        av_free_packet(&pkt);
    }

    if (bit_stream_filter_p) {
        av_bitstream_filter_close(bit_stream_filter_p);
    }

    if(format_context_p) {
        avformat_close_input(&format_context_p);
    }

    return 0;
}

 

转载于:https://my.oschina.net/xiaot99/blog/812983