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• libav C++ sw_scale returns variable byte size of BGR24 buffer

  6 mars 2021, par igor

  I'm trying to convert my local /dev/video0 cam to BGR24 format. It works if I resize the image (although not 100% of the time, more like 85% of the time), but I'd like to keep the same size as input video.

  


  I initialize BGR image like so including the sws context :

  


  AVPixelFormat outputPixFormat = AV_PIX_FMT_BGR24;

    AVFrame* pFrameBGR = av_frame_alloc();
    pFrameBGR->width = decoder->video_codec_context->width;
    pFrameBGR->height = decoder->video_codec_context->height;
    pFrameBGR->format = outputPixFormat;

    int alloRet = av_image_alloc(pFrameBGR->data, pFrameBGR->linesize, decoder->video_codec_context->width, decoder->video_codec_context->height, outputPixFormat, 1);
    if (alloRet < 0) {
        logging("failed to allocate image");
        return -1;
    }

    struct SwsContext *sws_ctx = NULL;

    sws_ctx = sws_getContext(decoder->video_codec_context->width,
    decoder->video_codec_context->height,
    decoder->video_codec_context->pix_fmt,
    decoder->video_codec_context->width,
    decoder->video_codec_context->height,
    outputPixFormat,
    SWS_DIRECT_BGR,
    0,
    0,
    0
    );


  


  This is the portion of my decoding loop :

  


  int response = avcodec_send_packet(pCodecContext, pPacket);
    if (response < 0) {
        logging("Error while sending a packet to decoder: %s", av_err2str(response));
        return response;
    }

    while (response >= 0) {
        response = avcodec_receive_frame(pCodecContext, pFrame);
         if (response == AVERROR(EAGAIN) || response == AVERROR_EOF) {
            break;
        } else if (response < 0) {
            logging("Error while receiving a frame from the decoder: %s", av_err2str(response));
            return response;
        }
        if (response >= 0) {

            sws_scale(sws_ctx,  (uint8_t const * const *)pFrame->data, pFrame->linesize, 0, pCodecContext->height, pFrameBGR->data, pFrameBGR->linesize);



  


  THe question is how to copy the plane of AVFrame into a buffer :

  


    size_t rgb_size = av_image_get_buffer_size(AV_PIX_FMT_BGR24, bgrFrame->width, bgrFrame->height, 1);

    uint8_t *dst_data;
    dst_data = (uint8_t *)(av_malloc(rgb_size));

    av_image_copy_to_buffer(dst_data, rgb_size, (const uint8_t* const *)bgrFrame->data, bgrFrame->linesize, AV_PIX_FMT_BGR24, bgrFrame->width, bgrFrame->height, 1);



  


  If I try to save to file the BGR image is correctly copied :

  


  char filebuf[256];
snprintf(filebuf, sizeof filebuf, "%s%d%s", "out_", pPacket->dts, ".rgb");
std::FILE *output=fopen(filebuf,"wb+");  

fwrite(bgrFrame->data[0],(pFrame->width)*(pFrame->height)*3,1,output);  
std::fclose(output);


  


  So it looks like my copy to buffer function is faulty, but I can figure out what's wrong with it :

  


    uint8_t *dst_data;
    dst_data = (uint8_t *)(av_malloc(rgb_size));

    av_image_copy_to_buffer(dst_data, rgb_size, (const uint8_t* const *)bgrFrame->data, bgrFrame->linesize, AV_PIX_FMT_BGR24, bgrFrame->width, bgrFrame->height, 1);


  


• Re-encoding vlc-created mpeg2 .ts file results in 20 second file ; AKA : multi-stream file with hidden streams

  6 septembre 2017, par insaner

  I was recording something with vlc off v4l2 (in case that makes a difference), and I just selected the first format that worked, being mpeg2 using TS container. File resulted in .ts extension, as automatically selected by vlc. When I then tried to put the video file in my video editor, it said the video was 19,884 hours long, when it should be about 6 minutes (it is 80mb in size). When I try to play it in xine, it correctly shows the duration (vlc doesn’t), and when I use ffprobe :

  [mpegts @ 0x9b2c0a0] max_analyze_duration 5000000 reached at 5000000
  
  Input #0, mpegts, from 'loopbacktestcap.ts':   Duration: N/A, start:
  
  17978.139456, bitrate: N/A   Program 1 
  
       Stream #0:0[0x44](): Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p, 640x480 [SAR 1:1 DAR 4:3], 104857 kb/s, 30 fps, 30
  
  tbr, 90k tbn, 60 tbc
  
       Stream #0:1[0x46](): Video: mpeg2video ([2][0][0][0] / 0x0002), 90k tbn

  Notice especially this line :

     Duration: N/A, start: 17978.139456, bitrate: N/A   Program 1 

  I looked it up and it seems the lack of duration has to do with the container. But I have tried a few things to reencode (I tried -vcodec copy, mpeg2, libx264...) and all I can get is 20 second files of 1.1mb - 1.8mb.

  So how can I reencode this file so the duration appears, and I get the full 6 minutes, instead of just the first 20 seconds ?

• Re-encoding vlc-created mpeg2 .ts file results in 20 second file ; AKA : multi-stream file with hidden streams

  23 novembre 2016, par insaner

  I was recording something with vlc off v4l2 (in case that makes a difference), and I just selected the first format that worked, being mpeg2 using TS container. File resulted in .ts extension, as automatically selected by vlc. When I then tried to put the video file in my video editor, it said the video was 19,884 hours long, when it should be about 6 minutes (it is 80mb in size). When I try to play it in xine, it correctly shows the duration (vlc doesn’t), and when I use ffprobe :

  [mpegts @ 0x9b2c0a0] max_analyze_duration 5000000 reached at 5000000
  
  Input #0, mpegts, from 'loopbacktestcap.ts':   Duration: N/A, start:
  
  17978.139456, bitrate: N/A   Program 1 
  
       Stream #0:0[0x44](): Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p, 640x480 [SAR 1:1 DAR 4:3], 104857 kb/s, 30 fps, 30
  
  tbr, 90k tbn, 60 tbc
  
       Stream #0:1[0x46](): Video: mpeg2video ([2][0][0][0] / 0x0002), 90k tbn

  Notice especially this line :

     Duration: N/A, start: 17978.139456, bitrate: N/A   Program 1 

  I looked it up and it seems the lack of duration has to do with the container. But I have tried a few things to reencode (I tried -vcodec copy, mpeg2, libx264...) and all I can get is 20 second files of 1.1mb - 1.8mb.

  So how can I reencode this file so the duration appears, and I get the full 6 minutes, instead of just the first 20 seconds ?