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• FFmpeg re-wrap of a TS-AAC audio transport stream file to M4A-AAC : what happens by default (no "-codec copy" etc.) ?

  22 avril 2022, par esp

  What happens if you simply do ffmpeg -i aFile.ts aFile.m4a as opposed to ffmpeg -i aFile.ts -codec copy aFile.m4a, when the TS file contains only a single stream, namely AAC, and knowing that m4a files also typically contain AAC.

  


  Does ffmpeg - even in the absence of any filters etc. - decode the original AAC and re-encode back to AAC (with whatever default parameters ffmpeg assumes for that - not necessarily matching those of the original) ? Or does it do something else ?

  


  I tried this both with and without "-codec copy" and the results in each case were AAC but the files were significantly different in size (Original TS : 8.5 MB, ffmpeg'd without "-codec copy" 7 MB, ffmpeg'd with latter 5.1 MB.

  


  At https://ffmpeg.org/ffmpeg.html it is stated (under "3.2 Stream copy"...

  


  


  Stream copy is a mode selected by supplying the copy parameter to the
-codec option. It makes ffmpeg omit the decoding and encoding step for the specified stream, so it does only demuxing and muxing. It is
useful for changing the container format or modifying container-level
metadata.
Implied by the inverse of that situation is that, in the absence of "-codec copy", ffmpeg will carry out the decoding and encoding steps.

  


  


• lavc/mediacodecdec : set codec profile and level from extradata for H264+HEVC

  13 décembre 2021, par sfan5

  lavc/mediacodecdec : set codec profile and level from extradata for H264+HEVC
  This value is later passed to MediaCodec and checked at decoder init.
  
  Notably decoding of 10-bit streams before this commit would "work" without
  
  returning errors but only return garbage output (on most Android devices).
  

  • [DH] libavcodec/mediacodecdec.c

• ffmpeg (IMAGE THUMBNAIL 1 frame) how to "choose" compression quality when we use -vframes 1 (how to do like convert -quality 60....)

  25 juillet 2021, par jini

  • PRE-CONTEXT : with ImageMagick, I'm use to do convert -quality 60 1.jpg 1.webp here "quality 60" affect the final size of the output

  


  • CONTEXT : create a poster.webp OR poster.jpg of a movie.mp4

  


  • QUESTION : how can we "achieve" the same compression level choice with ffmpeg when we want 1 frame

  


  • WHAT I TRIED [1] :

  


  ffmpeg -i movie.mp4 -vframes 1 -qmin 0 -qmax 1  0.webp

  


  and ffmpeg -i movie.mp4 -vframes 1 -qmin 50 -qmax 51 50.webp

  


  ==>> both gives the exact same size for the output.

  


  • WHAT I TRIED [2] :

  


  ffmpeg -i movie.mp4 -vframes 1 -b:v 9k bv9k.webp

  


  and ffmpeg -i movie.mp4 -vframes 1 -b:v 1k bv1k.webp

  


  ==>> both gives the exact same size for the output.

  


  what I'm I missing or miss using here ?

  


  Thanks