Ndtyjky

I writting a software for my classes that receive a h264 stream from a drone and i need to convert the video stream to opencv Mat.

I have no trouble to receive the frame and if i save it to a .264 file i can read the output with VLC.

The drone is sending IDR-Frame and P-Frame , since i don't need to see the video stream juste some frame of it, i was thinking of only using the IDR-Frame to get the image but i have trouble to understand how to use libavcodec from FFMPEG, how can i create a AVFrame from my IDR-Frame and how to convert it to cv::Mat after.

i have try the following code, i have store the full frame in .raw file and i try to decode them , but i get read error when i try to parse the packet to a frame, i don't thing a initialize the buffer of ARPacket the right way :

AVFormatContext* fc = 0;

int vi = -1; // vi veut dire video index





inline cv::Mat avframe_to_mat(const AVFrame* avframe) 

{

    AVFrame dst;

    cv::Mat m;



memset(&dst, 0, sizeof(dst));



int w = avframe->width, h = avframe->height;



m = cv::Mat(h, w, CV_8UC3);

dst.data[0] = (uint8_t*)m.data;



avpicture_fill((AVPicture*)&dst, dst.data[0], AV_PIX_FMT_BGR24, w, h);



struct SwsContext *convert_ctx = NULL;



enum AVPixelFormat src_pixfmt = AV_PIX_FMT_BGR24;

enum AVPixelFormat dst_pixfmt = AV_PIX_FMT_BGR24;



convert_ctx = sws_getContext(w, h, src_pixfmt, w, h, dst_pixfmt, SWS_FAST_BILINEAR, NULL, NULL, NULL);



sws_scale(convert_ctx, avframe->data, avframe->linesize, 0, h, dst.data, dst.linesize);

sws_freeContext(convert_ctx);



return m;



}



inline bool init_stream(unsigned char* data, int len)

{



const char* file = "test.avi";



const AVCodecID codec_id = AV_CODEC_ID_H264;

AVCodec* codec = avcodec_find_encoder(codec_id);

// Crée le container pour le stream

fc = avformat_alloc_context();



/*

AVOutputFormat *of = av_guess_format(0, file, 0);

fc = avformat_alloc_context();

fc->oformat = of;

strcpy(fc->filename, file);

*/

int br = 1000000;

int w = 640;

int h = 360;



int fps = 24;





// ajoute un stream video

AVStream* pst = avformat_new_stream(fc, codec); // Pourquoi je passe pas le codec ici ?

vi = pst->index;



codec_context = avcodec_alloc_context3(codec);



codec_context->bit_rate = br;

codec_context->width = w;

codec_context->height = h;

codec_context->time_base = {1,fps};

codec_context->gop_size = 10; // Emit one intra frame every ten frames

codec_context->max_b_frames = 1;

codec_context->pix_fmt = AV_PIX_FMT_YUV420P;



// Vu quon n'est en h264

av_opt_set(codec_context->priv_data, "preset", "slow", 0);





// Ouvre notre codec    

if(avcodec_open2(codec_context, codec,nullptr) < 0)

{

    cerr << "Impossible d'ouvrir le codec" << endl;

    return false;

}



if (!(fc->oformat->flags & AVFMT_NOFILE))

    avio_open(&fc->pb, fc->filename,0);



//  avformat_write_header(fc,nullptr);





return true;

}





inline void append_stream(uint8_t* data, int len)

{

if( 0 > vi)

{

    cerr << "video index is less than 0" << endl;

    return;

}

AVStream* pst = fc->streams[vi];



AVPacket pkt;





// Init un nouveau packet

av_init_packet(&pkt);

pkt.flags |= AV_PKT_FLAG_KEY;

pkt.data = data;

pkt.stream_index = pst->index;

pkt.size = len;



pkt.dts = AV_NOPTS_VALUE;

pkt.pts = AV_NOPTS_VALUE;



// ERROR accessing location

av_interleaved_write_frame(fc, &pkt);





}





inline void execute_staging_test(const fs::path& folder, int nbr_trame)

{

fs::path file_name = folder / "stream.bin";

if(!fs::exists(file_name))

{

    cerr << "The file " << file_name.string() << " does not exists" << endl;

    return;

}



avcodec_register_all();



av_log_set_level(AV_LOG_DEBUG);

int length = 0;

char* buffer;



for(int i = 0; i < nbr_trame;i++)

{

    fs::path file = std::to_string(i) + ".raw";

    file = folder / file;

    cout << "Got frame on " << file.string() << endl;

    ifstream ifs(file, ofstream::binary);



    // Get la longeur du fichier pour savoir le buffer a prendre

    ifs.seekg(0, ios::end);

    length = ifs.tellg();

    ifs.seekg(0, ios::beg);



    if (length == 0) {

        std::cerr << "No data in file " << file << std::endl;

        return;

    }



    buffer = new char[length];



    std::cout << "File " << file << " length is " << length << std::endl;



    ifs.read(buffer, length);



    cv::VideoWriter vw;

    int codec = cv::VideoWriter::fourcc('X', '2', '6', '4');





    if(!fc)

    {

        if(!init_stream((unsigned char*)buffer, length))

        {

            return;

        }

    }

    if(fc)

    {

        append_stream((unsigned char*)buffer, length);

    }   

}

}

Thanks you very mutch if you can help me , i'm a novice in c++ and i have never deal with video stream. If you want to see the full code its host on github repo to this project