libav

void video_parser::process_data(own_data *cd, const char *video_type) { // own_data has a std::vector<unsigned char> data
    AVCodec *codec;
    AVCodecContext *codec_context = NULL;
    AVPacket packet;
    AVFrame *frame;

    av_init_packet(&packet);

    if (strcmp(video_type, "mpeg1") == 0) {
        codec = avcodec_find_decoder(CODEC_ID_MPEG1VIDEO);
    }
    if (strcmp(video_type, "mp4") == 0) {
        codec = avcodec_find_decoder(CODEC_ID_MPEG4);
    }

    if (!codec) {
        std::cerr << "codec not found\n";
        exit(1);
    }

    codec_context = avcodec_alloc_context3(codec);
    if (!codec_context) {
        std::cerr << "could not allocate video codec context\n";
        exit(1);
    }

    frame = avcodec_alloc_frame();

    if (codec->capabilities & CODEC_CAP_TRUNCATED) {
        codec_context->flags |= CODEC_FLAG_TRUNCATED;
    }

    if (avcodec_open2(codec_context, codec, NULL) < 0) {
        std::cerr << "could not open codec\n";
        exit(1);
    }

    frame = avcodec_alloc_frame();
    if (!frame) {
        std::cerr << "could not allocate frame\n";
        exit(1);
    }

    int frame_count = 0;
    int got_frame;
    bool wrote_frame_to_disk = false;

    if (cd->get_buff_size() <= 0) {
        std::cerr << "no data available\n";
        exit(1);
    }
    //
    packet.size = cd->get_buff_size();
    packet.data = &cd->data[0];

    std::cout <<"packet.size: " << packet.size << std::endl;
    codec_context->width = 640;
    codec_context->height = 480;

    while (packet.size > 0) {
        int len = avcodec_decode_video2(codec_context, frame, &got_frame, &packet);
        std::cout <<"len: " << len << std::endl;
        if (len < 0) {
            std::cerr << "error while decoding frame " << frame_count << "\n";
            exit(1);
        }
        if (got_frame) {
            // do stuff
            frame_count++;
        }
        if (packet.data) {
            packet.size -= len;
            packet.data += len;
        }
    }

    std::cout << "found " << frame_count << " frames \n";

    packet.data = NULL;
    packet.size = 0;
    avcodec_close(codec_context);
    av_free(codec_context);
    avcodec_free_frame(&frame);