Recherche avancée

Sur d’autres sites (9831)

• lavc : Deprecate avctx.rtp_callback field

  19 novembre 2015, par Vittorio Giovara

  lavc : Deprecate avctx.rtp_callback field
  This function returns the encoded data of a frame, one slice at a time
  
  directly when that slice is encoded, instead of waiting for the full
  
  frame to be done. However this field has a debatable usefulness, since
  
  it looks like it is just a convoluted way to get data at lowest
  
  possible latency, or a somewhat hacky way to store h263 in RFC-2190
  
  rtp encapsulation.
  Moreover when multi-threading is enabled (which is by default) the order
  
  of returned slices is not deterministic at all, making the use of this
  
  function not reliable at all (or at the very least, more complicated
  
  than it should be).
  So, for the reasons stated above, and being used by only a single encoder
  
  family (mpegvideo), this field is deemed unnecessary, overcomplicated,
  
  and not really belonging to libavcodec. Libavformat features a complete
  
  implementation of RFC-2190, for any other case.
  Signed-off-by : Vittorio Giovara <vittorio.giovara@gmail.com>
  

  • [DBH] doc/APIchanges
  • [DBH] libavcodec/avcodec.h
  • [DBH] libavcodec/mpegvideo_enc.c
  • [DBH] libavcodec/version.h

• FFMPEG H264 with custom overlay per frame

  4 octobre 2020, par La bla bla

  We have a stream that is stored in the cloud (Amazon S3) as individual H264 frames. The frames are stored as framexxxxxx.264, the numbering doesn't start from 0 but rather from some larger number, say 1000 (so, frame001000.264)

  


  The goal is to create a mp4 clip which is either timelapse or just faster for inspection and other checking (much faster, compressing around 3 hours of video down to < 20 minutes), this also requires we overlay the frame number (the filename) on the frame itself

  &#xA;

  At first I was creating a timelapse by pulling from S3 only the keyframes (i-frames ? still rather new to codecs & stuff) and overlaying the filename on them and saving as png (which probably isn't needed, but that's what I did) using (this command is used inside a python script)

  &#xA;

  ffmpeg -y -i {h264_name} -vf \"scale=1920:-1, 
drawtext=fontfile=/usr/share/fonts/truetype/ubuntu-font-family/Ubuntu-B.ttf:fontsize=34:text={txt}:fontcolor=white:x=50:y=50:bordercolor=black:borderw=2\" 
-c:a copy -pix_fmt yuv420p {basename}.png


  &#xA;

  after this I combined all the frames by using python to convert the lowest numbered frame to 0.png and incrementing (so it would be continuous, because I only used keyframes the numbers originally weren't sequential) and running

  &#xA;

  ffmpeg -y -f image2 -i %d.png -r {self.params.fps} -vcodec libx264 -crf {self.params.crf} -pix_fmt yuv420p {out_file}


  &#xA;

  and this worked great, but the difference between keyframes was too long to allow for proper inspection

  &#xA;

  so now for the question(s)

  &#xA;

  since I know frames that are not keyframes (p-frames ?) can't be used alone by ffmpeg, the method of overlaying the file name and converting it to png (or keep as h264, same thing) won't work, or at least, I couldn't find a way for it to work, maybe there's a way to specify a frame's keyframe ?, how can one overlay the filename (and not the frame number as shown here for example)

  &#xA;

  Also, is it possible to skip some p-frames between the keyframes ? (so if a keyframe is every 30 frames, we would take a keyframe, a frame 15 frames later, and next another keyframe)

  &#xA;

  I thought about using ffmpeg's pipe option to feed it with the files as they're being downloaded, but I'm not sure if I can specify drawtext this way

  &#xA;

  Also, if there's another alternative that can achieve that (at first I was converting to png, using python and OpenCV to add the filename and then merging the pngs to mp4, but then I found drawtext can do that in a single command so I used it)

  &#xA;

• Anomalie #3991 : Erreur compression CSS et base64

  29 août 2017, par tcharlss (*´_ゝ｀)

  La ligne fautive se trouve ici : https://zone.spip.org/trac/spip-zone/browser/_core_/plugins/compresseur/inc/compresseur_minifier.php#L100

  // zero est zero, quelle que soit l’unite (sauf pour % car casse les @keyframes cf https://core.spip.net/issues/3128)
  $contenu = preg_replace("/([^0-9.]0)(em|px|pt)/ms", "$1", $contenu) ;
  

  Ça cherche le nombre zéro précédé de n’importe quel caractère (autre qu’un chiffre) ou d’un point.
  Du coup ça peut matcher avec les data URIs :
  

  @font-facefont-family :’spip’ ;src:url("data:application/font-woff ;base64,abc0pxyz") ;
  

  Pour éviter ce souci, on pourrait préciser exactement quels caractères peuvent précéder le zéro pour considérer qu’il s’agit d’une unité. On peut avoir :

  1) deux points
  

  font-size:0px ;
  

  2) un ou plusieurs espaces
  

  font-size : 0px ;
  font-size : calc(10px + 0px) ;
  

  3) une parenthèse dans le cas de calc()
  

  font-size : calc(0px) ;
  

  4) Autres unités

  À noter qu’il y a aussi pas mal d’autres unités qui ne sont pas prises en compte dans la regex actuelle : https://www.w3schools.com/cssref/css_units.asp
  

  rem ex pc
  vh vw vmin vmax 
  cm mm in
  ch 
  

  ---

  Ce qui donne au final la regex suivante, qui laisse mes data URIs tranquilles :
  

  $contenu = preg_replace("/((?: :|\s+|\()0)(em|px|pt|rem|ex|pc|vh|vw|vmin|vmax|cm|mm|in|ch)/ms", "$1", $contenu) ;