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• How to get the real, actual duration of an MP3 file (VBR or CBR) server-side

  27 janvier 2021, par SquareCat

  I used to calculate the duration of MP3 files server-side using ffmpeg - which seemed to work fine. Today i discovered that some of the calculations were wrong. Somehow, for some reason, ffmpeg will miscalculate the duration and it seems to happen with variable bit rate mp3 files only.

  



  When testing this locally, i noticed that ffmpeg printed two extra lines in green.

  



  Command used :

  



  ffmpeg -i song_9747c077aef8.mp3


  



  ffmpeg says :

  



  [mp3 @ 0x102052600] max_analyze_duration 5000000 reached at 5015510
[mp3 @ 0x102052600] Estimating duration from bitrate, this may be inaccurate


  



  After a nice, warm google session, i discovered some posts on this, but no solution was found.

  



  I then tried to increase the maximum duration :

  



  ffmpeg -analyzeduration 999999999 -i song_9747c077aef8.mp3


  



  After this, ffmpeg returned only the second line :

  



  [mp3 @ 0x102052600] Estimating duration from bitrate, this may be inaccurate


  



  But in either case, the calculated duration was just plain wrong. Comparing it to VLC i noticed that there the duration is correct.

  



  After more research i stumbled over mp3info - which i installed and used.

  



  mp3info -p "%S" song_9747c077aef8.mp3


  



  mp3info then returned the CORRECT duration, but only as an integer, which i cannot use as i need a more accurate number here. The reason for this was explained in a comment below, by user blahdiblah - mp3info is simply pulling ID3 info from the file and not actually performing any calculations.

  



  I also tried using mplayer to retrieve the duration, but just as ffmpeg, mplayer is returning the wrong value.

  


• How to get the real, actual duration of an MP3 file (VBR or CBR) server-side

  25 septembre 2016, par SquareCat

  I used to calculate the duration of MP3 files server-side using ffmpeg - which seemed to work fine. Today i discovered that some of the calculations were wrong. Somehow, for some reason, ffmpeg will miscalculate the duration and it seems to happen with variable bit rate mp3 files only.

  When testing this locally, i noticed that ffmpeg printed two extra lines in green.

  Command used :

  ffmpeg -i song_9747c077aef8.mp3

  ffmpeg says :

  [mp3 @ 0x102052600] max_analyze_duration 5000000 reached at 5015510
  
  [mp3 @ 0x102052600] Estimating duration from bitrate, this may be inaccurate

  After a nice, warm google session, i discovered some posts on this, but no solution was found.

  I then tried to increase the maximum duration :

  ffmpeg -analyzeduration 999999999 -i song_9747c077aef8.mp3

  After this, ffmpeg returned only the second line :

  [mp3 @ 0x102052600] Estimating duration from bitrate, this may be inaccurate

  But in either case, the calculated duration was just plain wrong. Comparing it to VLC i noticed that there the duration is correct.

  After more research i stumbled over mp3info - which i installed and used.

  mp3info -p "%S" song_9747c077aef8.mp3

  mp3info then returned the CORRECT duration, but only as an integer, which i cannot use as i need a more accurate number here. The reason for this was explained in a comment below, by user blahdiblah - mp3info is simply pulling ID3 info from the file and not actually performing any calculations.

  I also tried using mplayer to retrieve the duration, but just as ffmpeg, mplayer is returning the wrong value.

• FFmpeg : How do i use this script to concatenate incoming segments

  5 juillet 2017, par NGage

  I’d like to use this script but i don’t know how it should be applied. I was going to use it for encoding tv-shows and be able to start encoding as i had cut out the first segment.

  According to the ffmpeg-wiki (where i found the script) it says : "Concatenation becomes troublesome, if next clip for concatenation does not exist at the moment, because decoding won’t start until the whole list is read. However, it is possible to refer another list at the end of the current list :"

  Bear in mind that i dont know to much about bash

  #!/bin/bash
  
  
  
  fn_concat_init() {
  
  echo "fn_concat_init"
  
  concat_pls=`mktemp -u -p . concat.XXXXXXXXXX.txt`
  
  concat_pls="${concat_pls#./}"
  
  echo "concat_pls=${concat_pls:?}"
  
  mkfifo "${concat_pls:?}"
  
  echo
  
  }
  
  
  
  fn_concat_feed() {
  
  echo "fn_concat_feed ${1:?}"
  
  {
  
      >&2 echo "removing ${concat_pls:?}"
  
      rm "${concat_pls:?}"
  
      concat_pls=
  
      >&2 fn_concat_init
  
      echo 'ffconcat version 1.0'
  
      echo "file '${1:?}'"
  
      echo "file '${concat_pls:?}'"
  
  } >"${concat_pls:?}"
  
  echo
  
  }
  
  
  
  fn_concat_end() {
  
  echo "fn_concat_end"
  
  {
  
      >&2 echo "removing ${concat_pls:?}"
  
      rm "${concat_pls:?}"
  
      # not writing header.
  
  } >"${concat_pls:?}"
  
  echo
  
  }
  
  
  
  fn_concat_init
  
  
  
  echo "launching ffmpeg ... all.mkv"
  
  timeout 60s ffmpeg -y -re -loglevel warning -i "${concat_pls:?}" -pix_fmt 
  
  yuv422p all.mkv &
  
  
  
  ffplaypid=$!
  
  
  
  
  
  echo "generating some test data..."
  
  i=0; for c in red yellow green blue; do
  
  ffmpeg -loglevel warning -y -f lavfi -i testsrc=s=720x576:r=12:d=4 -pix_fmt 
  
  yuv422p -vf "drawbox=w=50:h=w:t=w:c=${c:?}" test$i.mkv
  
  fn_concat_feed test$i.mkv
  
  ((i++));
  
  echo
  
  done
  
  echo "done"
  
  
  
  fn_concat_end
  
  
  
  wait "${ffplaypid:?}"
  
  
  
  echo "done encoding all.mkv"