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• webm files created with ffmpeg are too long

  6 août 2022, par Azrael

  I have a folder of exactly 300 images in png format (labelled 1.png, 2.png, ..., 300.png), which I'm trying to convert to a video. I would like the video to be in the webm format, but there seems to be an issue :

  


  using the following command :

  


  ffmpeg -start_number 1 -i ./frames/%d.png -frames:v 300 -r 30 out.webm


  


  does generate an out.webm file, and, according to ffprobe -select_streams v -count_frames -show_entries stream=nb_read_frames,r_frame_rate out.webm (which is presumably quite an inefficient way to get that information, but that's besides the point), it does contain 300 frames and has a framerate of exactly 30/1, however, instead of the expected exactly 10 seconds (from 300 frames being played at 30 fps), the video lasts slightly longer (about 12 seconds).
  
This discrepancy does seem to scale up with video length ; 900 frames being converted to a video the same way and with the same frame rate yield a 36 (instead of 30) second video.

  


  For testing, I also tried generating an mp4 file instead of a webm one, with the following command (exact same as above, but out.mp4 instead of out.webm), and that worked exactly as expected, out.mp4 was a 10-second long video.

  


  ffmpeg -start_number 1 -i ./frames/%d.png -frames:v 100 -r 30 out.mp4


  


  How do I fix this ? is my ffmpeg command off or is this a bug within the tool ?

  


• Documentation #2846 : blocage des notification à cause d’une protection .htaccess

  3 mai 2013, par cedric -

  Je lis que l’on peut faire quelque chose comme
  

  SetEnvIf Request_URI ^spip.php~?action=cron$ bypass=1
  Satisfy any
  Order allow,deny
  
  Allow from env=bypass
  AuthUserFile ...
  
  AuthName ...
  
  AuthType Basic
  
  Require valid-user
  

  A tester

• Why do I get different codecs on Windows and Linux with same code ?

  27 janvier 2016, par user3277340

  I am using the API version of FFMPEG to generate a MP4 file from a series of images. I specify the output by calling

  AVFormatContext *oc = NULL ;
  avformat_alloc_output_context2 (&oc,NULL,"mp4",NULL) ;

  Running the exact same code on Windows and Linux I get different codecs assigned. On Windows, the value of oc->oformat->video_code is AV_CODEC_ID_H264 (28), but on Linux I get AV_CODEC_ID_MPEG4.

  I tracked this down because on Windows my calls to avcodec_encode_video2(.,.,.,&got_packet) were always returning got_packet=0 so I never called av_interleaved_write_frame. I added a NULL AVFrame at the end to flush the video. But it was very small and did not contain the images I expected to see there.

  But on Linux everything worked just fine. So I went ahead and manually changed the value of oc->oformat->video_code and I got the expected results.

  My questions :

  1) Why do I get different codec types on different platforms with the same code ? Is there a parameter I need to set to force MPEG4 ?

  2) Is it "legal" to change this parameter after the call to avformat_alloc_output_context2 ? My concern is that "oc" has been properly initialized and, with the change, something may be inconsistent.

  3) Is there a way to force the MPEG4 codec on any machine ?

  Thanks.