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• Use FFMPEG in OpenCV without internet connection

  17 novembre 2022, par Henalds

  I am creating a project in c++ with QtCreator (5.14.1, MingGW compiler) and trying to use OpenCv (3.4.16) to read video files. I have tried many files of standard formats and codecs (H.264, yuv420, .mov etc). However, no matter what I try, VideoCapture() always silently fails. It doesn’t crash or show any error code, instead isOpened() is just always false.

  


  I think the cause is that I am building opencv (via this tutorial https://wiki.qt.io/How_to_setup_Qt_and_openCV_on_Windows) without internet connection (I cannot have internet connection on this machine, so please do not ask me to) and therefore it can’t download the FFMPEG libraries during this process. I have been looking everywhere for information about how to download the FFMPEG libraries for opencv directly but I haven’t had any luck.

  


  Can someone please explain what libraries I need to download and how opencv goes about looking for them ? because at the moment I don’t know what I need, nor where to put them, and I cant find any information on the topic.

  


  Or, can someone explain why calling VideoCapture(“video.mov”, cv::CAP_ANY) doesn’t have any effect ? (despite being able to play the video easily in VLC, MediaPlayer etc).

  


  Code :
`

  


  int main()
{
    VideoCapture cap(“C://video.mov”);
    //VideoCapture cap(“C:/video.mov”);
    //VideoCapture cap(“C:\video.mov”);
    //VideoCapture cap(“C:\video.mov”);

    if (!cap.isOpened()){
        cout << "Error opening video stream or file"<< endl;
        return -1;
    }
}


  


  `

  


  I have tried downloading some ffmpeg DLLs and the EXEs and adding them to the PATH, no success. I have also tried downloading the shared GPL of ffmpeg (that comes with the libs and include) and added them my .pro file but no change in VideoCapture behavior.

  


  I have also tried moving the opencv_ffmpeg_64.dll (found in opencv/build/bin) to my executable directory but that didn't fix anything.

  


• ffmpeg scale down video dynamically (squeeze-back) or zoompan out to smaller than original VER2

  19 juillet 2023, par loarrin

  I have 2 videos, I'm trying to overlay one on top of the other, and have it shrink down in an animated fashion until it appears like a picture-in-picture setup. Then, after a few seconds it should scale back up. Just like in this question. Here is the working code from there :

  


  ffmpeg -i bg.mov -i top.mov -filter_complex "[0:v]scale=1920x1080,setpts=PTS-STARTPTS[bg]; [1:v]setpts=PTS-STARTPTS+2/TB, scale=-1:'480+600*abs(sin((t-2)*2*PI/8))':eval=frame[top]; [bg][top]overlay" -vcodec libx264 out.mp4


  


  It works perfectly, but I have one difference I cannot achieve modifying existing code : scale filter in this example resizes the second video stream having attraction point in the top left corner of this stream. I mean, when the second stream is getting smaller, it is scaled to the top left corner. And if it is getting bigger, it again stretches from the top left corner. The top left corner of the stream being scaled is staying in one place constantly no matter what.

  


  Is it possible to make more symmetrical version of this scale code, so when the second stream is scaled it is scaled from and to the top center of it (So the top left corner would move right when the stream is getting smaller and move to the left then the stream is getting bigger) ?

  


  

  


• How to play back images at high speed using ffmpeg

  12 octobre 2018, par yyms

  You are playing a video using FFmpegMediaPlayer
  . You can play normal, but are there options for fast playback and slow playback ?