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• 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

  


• aarch64 : vp9 : loop_filter : fix typo in skip flatout8 check

  14 novembre 2016, par Janne Grunau

  aarch64 : vp9 : loop_filter : fix typo in skip flatout8 check
  The 16_16 loop filter functions could miss an early exit before
  
  flatout8.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavcodec/aarch64/vp9lpf_neon.S

• Any other better ways to extract frames from a large size video according to the timecode given ?

  6 avril 2020, par Yong En

  Given a video from youtube with at least 600 MB. The video is annotated with labels that happens in multiple timecodes. The timecodes are in millisecond (SSSS.ss). I am trying to get the frames that fall within a time period (2 timecodes). There are TWO approaches that I used with different tools, one is using openCV in python and FFmpeg in bash script :

  



  I would stick with few variables here,

  



  

  • fps = 25

  


  • timecode (after convert into second) = 333.44 to 334.00 take note that I am dealing with time period that might less than a second.

  


  



  openCV

  



  

  1. Using openCV in python, I read the video as frames into a numpy array. Using the fps from video, 25. I can estimate where do the frames that fall under this time period by diving total video duration in second with length of the numpy array.

  


  2. Problem here is I will miss out some frames here due to the video fps is not really 25 as given by the video meta info, it could be 24.xx. Any solutions ?

  


  



  ffmpeg

  



  

  1. What I did, every time I want to get the frames, I run the script.

  


  2. Problem here is I need to read the video 100 times if I have 100 time periods. Any ways to overcome this ?

  


  



  Thanks for reading it.