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• lavfi/overlay : show incoming frames on debug messages

  20 juin 2014, par Stefano Sabatini

  lavfi/overlay : show incoming frames on debug messages
  This is especially useful to debug queue overflow issues.
  Ideally we should be able to set the debug message at the
  
  dualinput/framesync level, but they do not have the information related
  
  to the filter context and the inlink, so cannot access much useful
  
  information.
  Signed-off-by : Stefano Sabatini <stefasab@gmail.com>
  

  • [DH] libavfilter/vf_overlay.c

• How correctly show video with transparency in Qt with OpenCV + FFMpeg

  11 avril 2022, par TheEnigmist

  I'm trying to show a video with transparency in a Qt6 application using OpenCV + FFMPEG.
Actually those are tool versions :

  


  

  • Win 11

  


  • Qt 6.3.0

  


  • OpenCV 4.5.5 (built with CMake)

  


  • FFMPEG 2022-04-03-git-1291568c98-full_build-www.gyan.dev

  


  


  I've used a base .mov video with transparency as test (link provided below).
First of all I've converted .mov video to .webm video (VP9) and I see in output text that alpha channel remains

  


  


  ffmpeg -i '.\Retro Bars.mov' -c:v libvpx-vp9 -crf 30 -b:v 0 output.webm

  


  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2,
    ...
    Stream #0:0[0x1](eng): Video: qtrle (rle  / 0x20656C72), argb(progressive),
    ...

Output #0, webm, 
   ...
   Stream #0:0(eng): Video: vp9, yuva420p(tv, progressive),
   ...


  


  But when I show info of output file with ffmpeg it loses alpha channel :

  


  


  ffmpeg -i .\output.webm

  


  


  Input #0, matroska,webm,
    ...
    Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv, progressive),
    ...


  


  If I open output.webm with OBS it is shown correctly without a background, as shown in picture :


  


  If I try to open it with OpenCV + FFMPEG it shows a black background under bars, as shown in picture :


  


  This is how I load video in Qt :

  


  cv::VideoCapture capture;
capture.open(filename, cv::CAP_FFMPEG);
capture.set(cv::CAP_PROP_CONVERT_RGB, false); // try forcing load alpha channel
... //in a thread
while (capture.read(frame)) {
    qDebug() << "c" << frame.channels() << "t" <<  frame.type() << "d" <<  frame.depth(); // output: c 3 t 16 d 0
    cv::cvtColor(frame, frame, cv::COLOR_BGR2RGBA); //useless since no alpha channel is detected
    img = QImage(frame.data, frame.cols, frame.rows, QImage::Format_RGBA8888);
    emit processedImage(img); // to show image in a QLabel with QPixmap::fromImage(img)
}


  


  I think the problem is when I load the video with OpenCV, it doens't detect alpha channel, since I can load correctly in other player (obs, html5, etc.)

  


  What I'm wrong with all process to show this video in Qt with transparency ?

  


  EDIT : Added dropbox link with test video + ffmpeg outputs :
sample items

  


• Revision 047b0b01bb : Fix show existing frame - Disable mode info update in case where current frame

  5 décembre 2013, par Tero Rintaluoma

  Changed Paths :
   Modify /vp9/common/vp9_onyxc_int.h

  
   Modify /vp9/decoder/vp9_decodeframe.c

  
   Modify /vp9/decoder/vp9_onyxd_if.c

  
  
  Fix show existing frame

   Disable mode info update in case where current frame is coded
  as "show existing frame".
   Should fix issue 676.

  Change-Id : Ibee681850eb307f982da6528d3e31cb94f881c08