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• ffmpeg - multiple output with thumbnails

  9 décembre 2016, par Thomas

  I would like ffmpeg to do the following :

  • read an input mp4 (-i movie.mp4)
  • skip the first 5 seconds (-ss 5)
  • find scene changes and display the frame numbers (-vf "select=gt(scene\, 0.4, showinfo))
  • output #1 - a gif file (output.gif)
  • output #2 - a contact sheet with all the thumbnails (-vf "select scale=320 :-1, tile=12x200" thumbnails.png)

  This will generate the thumbnails :

  ffmpeg -hide_banner -i d:/Test/movie01.mp4 -ss 5 -vf "select=gt(scene\,0.4), showinfo, scale=320:-1, tile=12x200" -vsync 0 thumbnails%03d.png

  this will generate the gif :

  ffmpeg -hide_banner -i d:/Test/movie01.mp4 -ss 5 -vf "select='not(mod(n,60))',setpts='N/(30*TB)', scale=320:-1" -vsync 0 output.gif

  I would like to do both at once with 2 more features :

  • set fps and resolution for the gif ; I would like the gif to represent the whole movie in X seconds, at Y fps (I know the duration of the input movie so I can calculate how often a frame needs to be captured)

  • set the width only for the thumbnail picture (tile=12 for example) and let ffmpeg determine the appropriate height

  I have tried to compose a command line from what I read on this page : https://trac.ffmpeg.org/wiki/Creating%20multiple%20outputs, using the split / map commands but I couldn’t get it to work

• How to calculate ffmpeg output file size ?

  25 septembre 2011, par poundifdef

  I am using ffmpeg to convert home videos to DVD format and want to calculate the output file size before doing the conversion.

  My input file has a bit rate of 7700 kbps and is 114 seconds long. The audio bitrate is 256 kbit (per second ?) The input file is 77MB. To get this information I ran :

  mplayer -vo null -ao null -frames 0 -identify input.MOD

  So in theory, the input file should have (roughly) a file size of :

  ((7700 / 8) * 114) / 1024

  That is, (7700 / 8) is kilobytes/second, multiplied by 114 seconds, and then converted to megabytes. This gives me 107MB, which is way beyond my 77. Thus I am skeptical of his formula.

  That said, after converting the video :

  ffmpeg -i input.MOD -y -target ntsc-dvd -sameq -aspect 4:3 output.mpg

  The numbers seem to make more sense. Bitrate is 9000 kbps, and applying the above formula, I get 125MB, and my actual output file size is 126MB.

  So, two questions :

  1. How do I factor the audio bitrate into this calculation ? Is it additive (video file size + audio file size) ?

  2. Do DVDs always have a 9000 kilobit/second rate ? Is that the definition of a DVD ? Or might that change depending on video quality of my input video ? What does "-target ntsc-dvd" guarantee about my video ?

  3. Why does my input file not "match" the calculation, but the output file does ? Is there some other variable I'm not accounting for ?

  What is the correct way to calculate filesize ?

• avcodec/librav1e : Pass through timestamps as opaque user data

  17 mai 2020, par Derek Buitenhuis

  avcodec/librav1e : Pass through timestamps as opaque user data
  avcodec has no facilities to generate timestamps properly from
  
  output frame numbers (and it would be wrong for VFR anyway),
  
  so pass through the timestamps using rav1e's opaque user data
  
  feature, which was added in v0.4.0.
  This bumps the minimum librav1e version to 0.4.0.
  Signed-off-by : Derek Buitenhuis <derek.buitenhuis@gmail.com>
  

  • [DH] configure
  • [DH] libavcodec/librav1e.c