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• avcodec : clarify some decoding/encoding API details

  6 mars 2017, par wm4

  avcodec : clarify some decoding/encoding API details
  Make it clear that there is no timing-dependent behavior. In particular,
  
  there is no state in which both input and output are denied, and where
  
  you have to wait for a while yourself to make progress (apparently some
  
  hardware decoders like to do this).
  Avoid wording that makes references to time. It shouldn’t be mistaken
  
  for some kind of asynchronous API (like POSIX read() can return EAGAIN
  
  if there is no new input yet). It’s a state machine, so try to use
  
  appropriate terms.
  Signed-off-by : Diego Biurrun <diego@biurrun.de>
  Merges Libav commit 8a60bba0ae.
  

  • [DH] libavcodec/avcodec.h

• Embedding many small movies in page (gif vs mp4 vs webm vs ?)

  25 mars 2017, par genekogan

  I am making a webpage which will contain around 20-25 small-resolution ( 56x56) and short-length ( 3 sec) movies which will be set to autoplay and loop, so they will be looping on the page at all times. They are mostly dispersed throughout the page, so cannot easily be merged into bigger movies.

  I’m trying to decide on the right format to use, balancing filesize, quality, and processor overhead.

  mp4 seems the best option in terms of quality and filesize, however embedding many small mp4s on the page felt to me slow and made my computer get hot. Despite the fact that if they were one mp4, it would be only around 300x240 — it seems there is a lot of CPU overhead if they are divided.

  gif is lower quality and bigger filesize, but the CPU performance felt smoother. I can’t prove it though because I didn’t measure it — are gif’s known to be better performance than mp4 ?

  I have not tried other formats (webm, avi, ogg, etc) but I am unsure of how supported all of these formats are by most browsers and I want the webpage to be viewable from multiple browsers/countries.

  How can I determine the best format to use for these videos ? Is there a tool which can measure the CPU performance of my webpage so I can quantify the performance issues ?

• How to concatenate VP9-encoded video without re-encoding ?

  1er juin 2023, par ProgrammingLlama

  For H264 files, I'm currently using the following approach :

  


  

  1. First "prepare" the file for merging (I think unwrapping the byte stream from the overall encoded video ?) by using ffmpeg -i file.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts file.ts

  


  2. Concat the files into the resulting video using ffmpeg -i "concat:file1.ts|file2.ts" -c copy -bsf:a aac_adtstoasc out.mp4

  


  


  Now I'm trying to do the same with VP9 encoded files. I sense some step similar to (1) above is necessary, but I can't seem to find details on how I should do this. I'm currently just trying to concatenate the files like this :

  


  ffmpeg -i "concat:file1.webm|file2.webm" -c copy -bsf:v vp9_superframe out.webm`


  


  While this does merge the files (the resulting file size is approximately the same as the sum of the sizes of the input file), it doesn't actually merge the videos in terms of playback. Only the first video in the concatenation is playable (and the duration of the video matches the first).

  


  How is this done correctly with VP9 ?