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

  14 février 2017, par 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.

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

  10 décembre 2020, par 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.)

• ffmpeg Reduce frame rate

  10 juillet 2019, par 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]