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• Watch multi-stream video file while being recorded by ffmpeg

  20 janvier 2020, par Luke Gorrie

  I am using ffmpeg to record four 1080p video streams simultaneously and I would like to view these streams in real time while they are being recorded. Ideally I would like to view them from a separate machine, using some convenient Linux data sharing method like ssh/sshfs/..., but that is a nice-to-have. Is there a practical way to accomplish this ?

  The ffmpeg recording command that I currently use is like this :

  ffmpeg \
  
    -f v4l2 -i $cam0 \
  
    -f v4l2 -i $cam1 \
  
    -f v4l2 -i $cam2 \
  
    -f v4l2 -i $cam3 \
  
    -f matroska \
  
    -map 0 \
  
    -map 1 \
  
    -map 2 \
  
    -map 3 \
  
    -c copy \
  
    $output.mkv

  My problem would be solved if I could use a command like ffplay or vlc to play one or more of the video streams, always tracking close to the end of the stream, playing more as data becomes available. I haven’t found such an option though.

  One alternative might be to have the recording ffmpeg process also tile the four 1080p videos into one 4K grid and pipe that to ffplay. Then I could at least preview on the same machine that is recording. I have not been able to work out the right ffmpeg command to do the tiling though and would appreciate an example.

• Anomalie #4430 : image_reduire gère mal les arrondis

  4 février 2020, par jluc -

  J’ai ajouté des logs et vu que le pb est créé par image_ratio. La fonction n’est pas compliquée pourtant : https://code.spip.net/autodoc/tree/ecrire/inc/filtres_images_lib_mini.php.html#function_image_ratio

  J’ai testé sur l’image carrée en 427x427.
  À la fin j’ai ajouté un log à l’entrée qui témoigne que la fonction reçoit les arguments suivants : (427, 427, 200, 200) et un log à la fin qui montre ce qui va être renvoyé
  

  log("image_ratio renvoie ceil($destWidth)=".ceil($destWidth)
          .", ceil($destHeight)=".ceil($destHeight)
          .", max($ratioWidth, $ratioHeight)=".max($ratioWidth, $ratioHeight)) ;
  

  
  Et ça donne ça :
  

  image_ratio renvoie ceil(200)=200, ceil(200)=201, max(2.135, 2.135)=2.135
  

  Le 2eme "200" traîne un karma nano-décimal inconscient issu d’une mauvaise expérience d’arrondi à sa naissance ($destHeight = $srcHeight / $ratioWidth ; dans les lignes précédentes) et le ceil PHP en abuse violemment.

• Fix js MediaRecorder video file duration with js or ffmpeg

  20 juillet 2023, par NickG

  I am trying to create a playable video file with js MediaRecorder containing a video and audio stream. So far i managed to record the streams and create video files (.webm as default, .mp4 for Safari due to lacking .webm support).

  


  BUT : The recorded files are missing a duration when inspecting them or when opening them and are therefore not seekable in any videoplayer. For the .webm files i was able to resolve it by simply using this package and fixing the duration : https://github.com/yusitnikov/fix-webm-duration

  


  Unfortunetly, for .mp4 files this doesn't work. Any suggestions how i can fix the .mp4 files to be correctly playable in standard video players ?

  


  Sidenote :
I've also tried to postprocess the .mp4 files with ffmpeg on the server - without success. Weirdly enough, the conversion seems to work correctly on a windows machine, but not on a Unix machine (with the same command used, produces different output). If someone has experience with this, maybe he could guide me in the right direction how i could solve it via postprocessing ?