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• Use bash script with yt-download and ffmpeg to extract OR covert depending on format

  7 juin 2018, par Keyslinger

  I have a batch of files I uploaded to YouTube which I now wish to backup on my MacBook. When I download and extract the audio, I get either *.m4a or *. opus :

  #!/bin/sh
  
  ID="$1"
  
  
  
  youtube-dl -f bestaudio -x -i --audio-format best -o '%(playlist)s/%(playlist_index)s %(uploader)s - %(title)s.%(ext)s' https://www.youtube.com/playlist?list="$ID"

  When the file extension is m4a, I need to leave it that way and perform no conversion, when the extension is opus, I need to convert it to m4a.

  If I want to convert every file, I can do something like this :

  youtube-dl -f bestaudio -x -i --audio-format m4a -o '%(playlist)s/%(playlist_index)s %(uploader)s - %(title)s.%(ext)s' https://www.youtube.com/playlist?list="$ID"

  But then the conversion is performed no matter what.

  How can I extract and only convert when the file extension is not m4a ?

• ffmpeg extract subclips from video at 10s ; 30% ; 60% ; last 30s of a video

  2 juillet 2018, par martins

  I am writing Bash command on a Mac Terminal. To be able to use a loop, I’d like to extract 4 subclips of different inputfile .mp4 videos : 1st subclip (from second 10 to 20), 2nd subclip (10 seconds starting at a 33% stage of the inputfile), 3rd subclip (10 seconds starting at a 66% of the inputfile), and a 4th subclip (10 seconds starting 30seconds before the end of the inputfile).

  So far I only know how to make it work with fixed timings (i.e. seconds) but these correspond only to my first video (I have +200) :

  #!/bin/bash
  
  for file in *.mp4; do ffmpeg -i "$file" -vf "select='between(t, 10, 20) + between(t, 197, 207) + between(t, 393, 403) + between(t, 570,580)',
  
  setpts=N/FRAME_RATE/TB" -qscale 0 -af "aselect='between(t, 10, 20) + 
  
  between(t, 197, 207) + between(t, 393, 403) + between(t, 570, 580)', 
  
  asetpts=N/SR/TB" ${file%.mp4}_1.mp4; done

  For the first subclip, I always want from second 10 to 20, so I can leave it as it is, but for the 2nd to 4th subclip I need some formulas, but no idea which ones. Any suggestions ?

  Thanks for your time

• DVD m2v to mp4, Anamorphic to Square Pixels, 640x480 or 720x540 ?

  10 juillet 2018, par Matt McManis

  I want to use FFmpeg to convert an NTSC DVD .m2v file to an .mp4.

  The original resolution is 720x480 4:3 Anamorphic.

  I want to convert for playback on a computer using a player like VLC, with Square Pixels.

  ---

  To preserve the best quality

  Should I convert stretching the height 720x540 ?

  Or shrink the width 640x480 ?

  Or should I leave it Anamorphic 720x480 ?

  ---

  What is the difference between playing Anamorphic and Square Pixels on a computer monitor ?

  Does the media player always stretch the pixels to display correctly if Anamorphic ?

  Does encoding the height stretch from 480 to 540 by FFmpeg improve anything ?

  ---

  FFmpeg

  ffmpeg
  
  
  
  -framerate ntsc 
  
  
  
  -i input.m2v 
  
  
  
  -c:v libx264 
  
  -preset medium -crf 18 
  
  -pix_fmt yuv420p 
  
  
  
  -s 720x540 
  
  -aspect 4:3 
  
  
  
  -vf "fps=24000/1001" 
  
  
  
  output.mp4