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• ffmpeg Reduce frame rate

  10 July 2019, by Chieron

  I am trying to convert h264 vids to h265. Some of the vids are 50fps and seem to have a lot of duplicate frames(100000+). I guess these are 25fps vids and somehow they have every frame duplicated.

  ffmpeg is not dropping the frames it seems and so I guess this is wasting space(although I’d hope very little but it’s probably not optimal).

  I’d like to fix this though.

  is there a way to set the frame rate to 30, say(-r 30) and have ffmpeg correctly keep everything in sync(audio aligned properly) and not have any real issues? this might require interpolation and all that but I definitely do not want the audio to be off(it’s crucial) and I don’t want the length to change.

  I’m not sure if I can just specify -r 30 and everything will work out, if it even matters(maybe h265 handles these duplicates very efficiently?), or if I need to specify more?

  So, in some sense, I’m actually increasing the frame rate(if it is 25fps and I’m going to 30, hence the interpolation).

  I also have a lot of videos that this happened to. Is there any efficient way to go back and recode them if necessary?

  What are the compression consequences of having these duplicate frames in h265? Does it store them very efficiently or am I wasting space?

  I have a few hundred GB of files and probably a lot have this issue as I didn’t know what was going on and didn’t investigate it but saw the message a lot. I actually thought it was just some meaningless error since it was clear the video was consistent with the other. If 100k duplicate frames would imply a static video but it didn’t occur to me that someone would duplicate every frame(since that would simply waste space). [I tried to search but little exists about this specific issue]

• Evolution #4613 (Nouveau): créer une aide ré-actualisée pour Spip 3.*

  10 December 2020, by Laurent Lefebvre

  Bonjour,

  quelques affirmations concernant les retours à la ligne sont fausses depuis Spip 3.0 :

  Ex :

  • "Le fait de simplement « revenir à la ligne » (retour-chariot) sans séparer les deux paragraphes par une ligne vide ne suffit pas pour provoquer un changement de paragraphe (cela ne provoque même pas un retour à la ligne)._" -> Il faudrait retirer la parenthèse et son contenu.
  • "Notez : ici un simple retour à la ligne suffit (on peut faire des énumérations dans le même paragraphe) ; mais si l’on « saute » une ligne avant la ligne commençant par un tiret, une ligne vide est affichée avant l’énumération._" -> Ce paragraphe ne sert plus dans le contexte Spip 3.*

  On pourrait aussi moderniser l’aide. Ajouter la mention aux touches raccourcis par exemple ( pour l’italique, le gras, les intertitres ... ).
  En attendant ce changement, ne pourrait-on pas modifier rapidement les affirmations sur les retours à la ligne ? (c’est crucial pour les nouveaux utilisateurs et ce sont eux qui utilisent l’aide.)

• How to efficiently create H264 mpeg from two clips with known different motion intensity?

  14 February 2017, by Serge

  Given an audio and an image we create a static image "video" and then append a short clip that has a rather intense motion.

  Audio and image varies from run to run. Appended animation is always the same. Rendering is done with ffmpeg on a remote server. Rendered file must be in h264 codec mpg.

  Speed of encoding is crucial. Is there a fast and effective way to generate and merge the two clips quickly?

  Atm we use the following ffmpeg commands:

  // create first clip from image
  
  ffmpeg -loop 1 -r 24 -i $IMAGE -i $AUDIO -t $AUDIO_LENGTH -c:a aac -profile:a aac_low -ar 48000 -b:a 192k -bsf:a aac_adtstoasc -strict -2 -y -c:v libx264 -profile:v high -preset veryfast  -tune stillimage -crf 24 -x264opts bframes=2 -pix_fmt yuv420p -safe 0  clip1.mpg
  
  // . . .
  
  // then append the animation
  
  ffmpeg -f concat -safe 0 -i list.txt -c copy -y -safe 0 final.mpg 

  Intuition is that we can benefit form knowing exact timing of a first clip with a static image and the second one with intense animation – like it is determined in the 1-st pass of a 2-pass compression.

  Someone experienced in tech of h264 codec and mpeg please advice.