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• ffmpeg select subclips from large video bash and create outputfile names

  29 juin 2018, par martins

  I am using bash command on a Mac Terminal. For each of the 250 .mp4 files in a directory I need to create a new outputfile which extracts 4 subclips from each inputfile : 1st subclip (from second 10 to 20), 2nd subclip (10 seconds at a 33% stage of the inputfile), 3rd subclip (10 seconds at a 66% of the inputfile), and a 4th subclip (10 seconds starting 30seconds before the end of the inputfile). Each inputfile has a different length of about 10-15minutes.

  I tried with one inputfile and the following bash script works :

  #!/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" outputfile.mp4; done

  However, I don’t know how to loop it over the 250 mp4 files. Specifically, I have 2 issues :

  1. The above code shows specific seconds I manually checked from the inputfile I used to test the code. I need to automatize the code according to the timings above.
  2. Name the outputfile the same as the inputfile but adding "_1" suffix

  In sum, I have a directory with inputfiles between 10-15minutes long :

  inputfile1.mp4
  
  inputfile2.mp4
  
  inputfile3.mp4
  
  .......
  
  inputfile250.mp4

  And I want the same directory with inputfiles and outputfiles together :

  inputfile1.mp4
  
  inputfile1_1.mp4 #this is 40 seconds long
  
  inputfile2.mp4
  
  inputfile2_1.mp4 #this is 40 seconds long
  
  inputfile3.mp4
  
  inputfile3_1.mp4 #this is 40 seconds long
  
  .......
  
  inputfile250.mp4
  
  inputfile250_1.mp4 #this is 40 seconds long

  Thank you very much in advance.

• avconv "select" filter doesn't discard first frames

  1er avril 2014, par user2152106

  I'm trying to segment a video using avconv's "select" filter to extract only a specific range of frames from the input file. As an example, imagine I have a 60fps video file called input.mp4, with 3000 frames (i.e. 50 seconds), and I run

  avconv -i input.mp4 -vf "select='lt(n,2000)'" output1.mp4
  
  avconv -i input.mp4 -vf "select='gte(n,2000)'" output2.mp4

  What I expect is that output1.mp4 has the first 2000 frames of input.mp4 (and lasts 33 seconds), and output2.mp4 has the last 1000 (and lasts 17 seconds).

  I count the frames by running

  avconv -i video.mp4 -vcodec copy -an -f null /dev/null 2>&1 | grep 'frame='

  and checking the value assigned to 'frame'.

  What I actually get, is that output1.mp4 has 2000 frames and lasts 33 seconds, but output2.mp4 has 2999 frames, and still lasts the full 50 seconds. When I open output2.mp4, I notice that the first 2000 frames of the video are actually just a repetition of the 2000th frame of the input, i.e. the first 2000 frames seem to be correctly filtered, but replaced by the first of the accepted frames.

  This is not a pts problem. I check the number of packets and their relative pts using avprobe :

  avprobe -show_packets output2.mp4
  
  echo $(avprobe -show_packets output2.mp4 2>/dev/null | grep PACKET | wc -l)/2 | bc

  I see that there are actually 2999 packets.

  What am I doing wrong ?

  Side questions :

  • Assuming I'm doing something wrong, why does output2.mp4 contain 2999 rather than the full 3000 ?
  • The behaviour doesn't change whether I use the "gte" or "gt" function in the filter. Why could that be ?

• avcodec/av1dec : add an option to select an operating point

  15 novembre 2020, par James Almer

  avcodec/av1dec : add an option to select an operating point
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] doc/decoders.texi
  • [DH] libavcodec/av1dec.c
  • [DH] libavcodec/av1dec.h