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• Record specific window using ffmpeg

  5 décembre 2022, par Ahmed A. Mansour

  I have been trying the below code (which I found on other similiar problem on this site here : How to record a specific window using ffmpeg But it gives me black video and the same video is not playable by windows media player (it works on vlc but with black video..)

  


  ffmpeg -f gdigrab -framerate 30 -i title="german.avi - VLC media player" -b:v 3M  germ.flv


  


  Video example :
Weird thumbnail by WMP which shows it can't play it
Black screen as described, but it opens with black video in VLC

  


  I tried the other suggestions, but this one sometimes (less than 40% of the time) works.
I also noticed it doesn't show the window main title, which is a bit confusing, as it causes the mouse cursor to appear a little down where it should be.

  


• Cannot get first frames using av_seek_file

  31 janvier 2014, par JonesV

  I want to seek for an arbitrary frame in a video using libav. More precisely, using the function avformat_seek_file, which apparently uses av_seek_frame internally.

  I want to make a backward search (i.e. to get the closest possible frame before the one I seek), so that I can then go forward until I find precisely the one I want. For this, I use the function as follows :

  avformat_seek_file(..., ...,
  
                     std::numeric_limits::min(),
  
                     target_pts,
  
                     target_pts,
  
                     ...);

  Which means that I don't have any tolerance about finding a frame that comes after my target_pts, but I am happy with any frame coming before.

  I am using the Big Buck Bunny videos for testing. Using the 480p H.264 video, I can seek any pts without problems. But using the 480p OGG video, I can't. Actually, I can seek for any frame after pts = 73, but not before. Seeking for pts = 0 sets the video to pts = 73.

  One might think that the stream actually begins at pts = 73, but this is not what <stream>.start_time</stream> returns. Moreover, if I only load the video and read the frames in order, I can get the first 73 frames without any problem. The issue is that I can never come back to one of those frames by using avformat_seek_file.

  Last point : if I use the flag AVSEEK_FLAG_ANY, then it works. But that might result in me decoding only a part of the frame I want, which is not a solution for me.

  Can anybody explain this weird behavior ?

• Cannot get first frames using avformat_seek_file

  14 octobre 2015, par JonesV

  I want to seek for an arbitrary frame in a video using libav. More precisely, using the function avformat_seek_file, which apparently uses av_seek_frame internally.

  I want to make a backward search (i.e. to get the closest possible frame before the one I seek), so that I can then go forward until I find precisely the one I want. For this, I use the function as follows :

  avformat_seek_file(..., ...,
  
                     std::numeric_limits::min(),
  
                     target_pts,
  
                     target_pts,
  
                     ...);

  Which means that I don’t have any tolerance about finding a frame that comes after my target_pts, but I am happy with any frame coming before.

  I am using the Big Buck Bunny videos for testing. Using the 480p H.264 video, I can seek any pts without problems. But using the 480p OGG video, I can’t. Actually, I can seek for any frame after pts = 73, but not before. Seeking for pts = 0 sets the video to pts = 73.

  One might think that the stream actually begins at pts = 73, but this is not what <stream>.start_time</stream> returns. Moreover, if I only load the video and read the frames in order, I can get the first 73 frames without any problem. The issue is that I can never come back to one of those frames by using avformat_seek_file.

  Last point : if I use the flag AVSEEK_FLAG_ANY, then it works. But that might result in me decoding only a part of the frame I want, which is not a solution for me.

  Can anybody explain this weird behavior ?