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• FFMPEG show an Image with specific duration in filter_complex chain

  26 juin 2021, par Digerkam

  I have trouble with showing images with a specific duration in filter_complex.

  


  I have to use filter_complex, and getting error : "No such filter : 'duration'"

  


  So which filter do I need to use ?

  


  ffmpeg \
    -i "music.mp3" \
    -i "01.mp4" \
    -i "02.jpg" \
    -i "03.mp4" \
    -i "04.jpg" \
    -i "05.mp4" \
    -filter_complex " \
        [1:v]scale=300:400,trim=0:2,setpts=PTS-STARTPTS[v1]; \
        // Correct filter needed here: \
        [2:v]scale=300:400,duration=2,setpts=PTS-STARTPTS[v2]; \
        [3:v]scale=300:400,trim=4:6,setpts=PTS-STARTPTS[v3]; \
        // And here:
        [4:v]scale=300:400,duration=2,setpts=PTS-STARTPTS[v4]; \
        [5:v]scale=300:400,trim=8:10,setpts=PTS-STARTPTS[v5]; \
        [v1][v2][v3][v4][v5]concat=n=5:v=1:a=0[out] \
    " \
    -map "[out]" -map "0:a" -t "12" -c:v "libx264" -pix_fmt "yuv420p" -s "300x400" output.mp4


  


• In ffmpeg command-line, how to show all filter settings and their parameters before encoding ?

  7 décembre 2023, par F.X.

  Is there a way to force the ffmpeg command-line to display a comprehensive list of all filters and their parameters, even those that are applied automatically like -vf scale ?

  


  (EDIT : To clarify, I do not mean filter documentation, but rather displaying filters that are instantiated at runtime for a particular command-line, just before transcoding starts. The goal of this is mostly checking that ffmpeg is indeed doing the right thing and not inserting/changing filters when I do not intend it to.)

  


  There are a few options available, but none are comprehensive enough. For example :

  


  

  • The lavfi module has a dumpgraph option (here) but only if you're using lavfi.

  


  • The -sws_flags print_info option (here) can be used to determine if -vf scale is applied automatically and shows a subset of its parameters, but not all of them.

  


  


  Additionally, this question appears related the answer doesn't answer what I'm looking for.

  


  Are there better ways to achieve that ?

  


• 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