如何使用 FFmpeg 和 C/C++ 将数据流添加到 MXF（使用 mpeg2video）文件中

Question

I'm a little bit stuck here trying create a MXF file with data stream on it. I have several MXF video files that contain this standard

**1 Video Stream:
     Stream #0:0: Video: mpeg2video (4:2:2), yuv422p(tv, bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], 50000 kb/s, 29.9
16 audio streams
     Audio: pcm_s24le, 48000 Hz, 1 channels, s32 (24 bit), 1152 kb/s
1 Data Stream:
     Data: none**

This data stream, contain personal data inside video file. I can open this stream and data is really there. Is all ok. But, when i try to create a file exactly like this, everytime i call "avformat_write_header" it returns an error.

If i do comment the creation of this data streams the video file is succeffully created.

If i change to "mpegts" with this data stream, the video file is also succeffully created.

But, i can't use mpets and i need this data stream.

I know that is possible MXF with data stream cause i have this originals files that have this combination.

So, i know that i missing something in my code.

This is the way i create this Data Stream:

 void CFFmpegVideoWriter::addDataStream(EOutputStream *ost, AVFormatContext *oc, AVCodec **codec, enum AVCodecID codec_id)
    {
        AVCodecParameters *par;

        ost->stream = avformat_new_stream(oc, NULL);
        if (ost->stream == NULL)
        {
            fprintf(stderr, "OOooohhh man: avformat_new_stream() failed.\n");
            return;
        }

        par = ost->stream->codecpar;
        ost->stream->index = 17;
        par->codec_id = AV_CODEC_ID_NONE;
        par->codec_type = AVMEDIA_TYPE_DATA;

        ost->stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }

the file openning is this:

CFFMpegVideoWriter::CFFMpegVideoWriter(QString outputfilename) : QThread()
{
    av_register_all();
    avcodec_register_all();

    isOpen = false;
    shouldClose = false;

    frameIndex = 0;

#ifdef __linux__
    QByteArray bFilename = outputfilename.toUtf8();
#else
    QByteArray bFilename = outputfilename.toLatin1();
#endif

    const char* filename = bFilename.data();

    codecContext = NULL;

    //encontra o formato desejado...
    outputFormat = av_guess_format("mp2v", filename, nullptr);
    if (!outputFormat)
    {
        qDebug("Could not find suitable output format\n");
        return;
    }

    //encontra o codec...
    codec = avcodec_find_encoder(outputFormat->video_codec);
    if (!codec)
    {
        qDebug( "Codec not found\n");
        return;
    }

    //aloca o contexto do codec...
    codecContext = avcodec_alloc_context3(codec);
    codecContext->field_order = AV_FIELD_TT;
    codecContext->profile = FF_PROFILE_MPEG2_422;

    //aloca o contexto do formato...
    formatContext = avformat_alloc_context();
    formatContext->oformat = outputFormat;

    //aloca o contexto da midia de saida...
    avformat_alloc_output_context2(&formatContext, NULL, NULL, filename);
    if (!formatContext)
    {
        qDebug("Erro");
        return;
    }

    videoStream.tmp_frame = NULL;
    videoStream.swr_ctx = NULL;

    //adiciona a stream de video...
    if (outputFormat->video_codec != AV_CODEC_ID_NONE)
    {
        addVideoStream(&videoStream, formatContext, &video_codec, outputFormat->video_codec);       
    }

    //adiciona as 16 streams de audio...
    if (outputFormat->audio_codec != AV_CODEC_ID_NONE)
    {
        for (int i = 0; i < 16; i++)
        {
            addAudioStream(&audioStream[i], formatContext, &audio_codec, outputFormat->audio_codec);
        }       
    }

    addDataStream(&datastream, formatContext, &video_codec, outputFormat->video_codec);     

    videoStream.sws_ctx = NULL;
    for (int i = 0; i < 16; i++)
    {
        audioStream[i].sws_ctx = NULL;
    }   
    opt = NULL;


    //carreca o codec de video para stream de video...      
    initVideoCodec(formatContext, video_codec, &videoStream, opt);


    //carrega o codec de audio para stream de audio...s
    for (int i = 0; i < 16; i++)
    {
        initAudioCodec(formatContext, audio_codec, &audioStream[i], opt);
    }


    av_dump_format(formatContext, 0, filename, 1);

    //abrea o arquivo de saida..
    if (!(outputFormat->flags & AVFMT_NOFILE))
    {
        ret = avio_open(&formatContext->pb, filename, AVIO_FLAG_WRITE);
        if (ret < 0)
        {
            qDebug("Could not open'%s", filename);
            return;
        }
    }

    //escreve o cabecalho do arquivo...
    ret = avformat_write_header(formatContext, &opt);
    if (ret < 0)
    {
        qDebug("Error occurred when opening output file");
        return;
    }

    isOpen = true;

    QThread::start();
}

The code always fails at "avformat_write_header" call.

But if i remove "datastream" or change it to mpegts everything runs fine.

Any ideia of what am i doing wrong here?

Thanks for reading this.

Helmuth

Answer 1

After some long hours trying a lot of solutions i found what was wrong. I had to add a metadata item specifing data type.

In my case, data type was "vbi_vanc_smpte_436M" wich is supported by MXF.

so, i dit with:

av_dict_set(&out_stream->metadata, "data_type", "vbi_vanc_smpte_436M",  AV_DICT_IGNORE_SUFFIX);  

Then everything works fine.

I hope this can help anyone else with same problem.