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• How can I detect which audio channels in a video file are silent using FFMPEG ? [migrated]

  15 mars 2024, par kfank

  I need to be able to scan video files and report which audio tracks/channels are silent without knowing anything about the file's audio mapping ahead of time. I have tried this ffmpeg (v4.1) command on a file that contains 16 audio channels :

  


  $ ffmpeg -i foo5.mxf -map 0:a -af astats -f null -
...
Stream mapping:
  Stream #0:1 -> #0:0 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:2 -> #0:1 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:3 -> #0:2 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:4 -> #0:3 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:5 -> #0:4 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:6 -> #0:5 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:7 -> #0:6 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:8 -> #0:7 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:9 -> #0:8 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:10 -> #0:9 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:11 -> #0:10 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:12 -> #0:11 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:13 -> #0:12 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:14 -> #0:13 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:15 -> #0:14 (pcm_s24be (native) -> pcm_s16le (native))
  Stream #0:16 -> #0:15 (pcm_s24be (native) -> pcm_s16le (native))
...
[Parsed_astats_0 @ 0x9123c0] Channel: 1
[Parsed_astats_0 @ 0x9123c0] DC offset: 0.000070
[Parsed_astats_0 @ 0x9123c0] Min level: -170426368.000000
[Parsed_astats_0 @ 0x9123c0] Max level: 172195840.000000
[Parsed_astats_0 @ 0x9123c0] Min difference: 0.000000
[Parsed_astats_0 @ 0x9123c0] Max difference: 58281984.000000
[Parsed_astats_0 @ 0x9123c0] Mean difference: 3089081.855667
[Parsed_astats_0 @ 0x9123c0] RMS difference: 4825348.720329
[Parsed_astats_0 @ 0x9123c0] Peak level dB: -21.918144
[Parsed_astats_0 @ 0x9123c0] RMS level dB: -34.035425
[Parsed_astats_0 @ 0x9123c0] RMS peak dB: -27.320939
[Parsed_astats_0 @ 0x9123c0] RMS trough dB: -48.414915
[Parsed_astats_0 @ 0x9123c0] Crest factor: 4.035190
[Parsed_astats_0 @ 0x9123c0] Flat factor: 0.000000
[Parsed_astats_0 @ 0x9123c0] Peak count: 2
[Parsed_astats_0 @ 0x9123c0] Bit depth: 20/20
[Parsed_astats_0 @ 0x9123c0] Dynamic range: 98.493854
[Parsed_astats_0 @ 0x9123c0] Zero crossings: 10216
[Parsed_astats_0 @ 0x9123c0] Zero crossings rate: 0.042383
[Parsed_astats_0 @ 0x9123c0] Overall
[Parsed_astats_0 @ 0x9123c0] DC offset: 0.000070
[Parsed_astats_0 @ 0x9123c0] Min level: -170426368.000000
[Parsed_astats_0 @ 0x9123c0] Max level: 172195840.000000
[Parsed_astats_0 @ 0x9123c0] Min difference: 0.000000
[Parsed_astats_0 @ 0x9123c0] Max difference: 58281984.000000
[Parsed_astats_0 @ 0x9123c0] Mean difference: 3089081.855667
[Parsed_astats_0 @ 0x9123c0] RMS difference: 4825348.720329
[Parsed_astats_0 @ 0x9123c0] Peak level dB: -21.918144
[Parsed_astats_0 @ 0x9123c0] RMS level dB: -34.035425
[Parsed_astats_0 @ 0x9123c0] RMS peak dB: -27.320939
[Parsed_astats_0 @ 0x9123c0] RMS trough dB: -48.414915
[Parsed_astats_0 @ 0x9123c0] Flat factor: 0.000000
[Parsed_astats_0 @ 0x9123c0] Peak count: 2.000000
[Parsed_astats_0 @ 0x9123c0] Bit depth: 20/20
[Parsed_astats_0 @ 0x9123c0] Number of samples: 241040
[Parsed_astats_0 @ 0x4def40] Channel: 1
[Parsed_astats_0 @ 0x4def40] DC offset: 0.000070
[Parsed_astats_0 @ 0x4def40] Min level: -170426368.000000
[Parsed_astats_0 @ 0x4def40] Max level: 172199936.000000
[Parsed_astats_0 @ 0x4def40] Min difference: 0.000000
[Parsed_astats_0 @ 0x4def40] Max difference: 58277888.000000
[Parsed_astats_0 @ 0x4def40] Mean difference: 3089075.891088
[Parsed_astats_0 @ 0x4def40] RMS difference: 4825346.346176
[Parsed_astats_0 @ 0x4def40] Peak level dB: -21.917938
[Parsed_astats_0 @ 0x4def40] RMS level dB: -34.035425
[Parsed_astats_0 @ 0x4def40] RMS peak dB: -27.320942
[Parsed_astats_0 @ 0x4def40] RMS trough dB: -48.414908
[Parsed_astats_0 @ 0x4def40] Crest factor: 4.035287
[Parsed_astats_0 @ 0x4def40] Flat factor: 0.000000
[Parsed_astats_0 @ 0x4def40] Peak count: 2
[Parsed_astats_0 @ 0x4def40] Bit depth: 20/20
[Parsed_astats_0 @ 0x4def40] Dynamic range: 98.494061
[Parsed_astats_0 @ 0x4def40] Zero crossings: 10220
[Parsed_astats_0 @ 0x4def40] Zero crossings rate: 0.042400
[Parsed_astats_0 @ 0x4def40] Overall
[Parsed_astats_0 @ 0x4def40] DC offset: 0.000070
[Parsed_astats_0 @ 0x4def40] Min level: -170426368.000000
[Parsed_astats_0 @ 0x4def40] Max level: 172199936.000000
[Parsed_astats_0 @ 0x4def40] Min difference: 0.000000
[Parsed_astats_0 @ 0x4def40] Max difference: 58277888.000000
[Parsed_astats_0 @ 0x4def40] Mean difference: 3089075.891088
[Parsed_astats_0 @ 0x4def40] RMS difference: 4825346.346176
[Parsed_astats_0 @ 0x4def40] Peak level dB: -21.917938
[Parsed_astats_0 @ 0x4def40] RMS level dB: -34.035425
[Parsed_astats_0 @ 0x4def40] RMS peak dB: -27.320942
[Parsed_astats_0 @ 0x4def40] RMS trough dB: -48.414908
[Parsed_astats_0 @ 0x4def40] Flat factor: 0.000000
[Parsed_astats_0 @ 0x4def40] Peak count: 2.000000
[Parsed_astats_0 @ 0x4def40] Bit depth: 20/20
[Parsed_astats_0 @ 0x4def40] Number of samples: 241040
...


  


  By piping to grep (and a little more filtering) I can consolidate this and examine the peak levels on the audio channels :

  


  $ ffmpeg -i foo5.mxf -map 0:a -af astats -f null - 2>&1 | grep -E "(Channel:|Peak level|Overall)"
[Parsed_astats_0 @ 0x9123c0] Channel: 1
[Parsed_astats_0 @ 0x9123c0] Peak level dB: -21.918144
[Parsed_astats_0 @ 0x9123c0] Overall
[Parsed_astats_0 @ 0x9123c0] Peak level dB: -21.918144
[Parsed_astats_0 @ 0x4def40] Channel: 1
[Parsed_astats_0 @ 0x4def40] Peak level dB: -21.917938
[Parsed_astats_0 @ 0x4def40] Overall
[Parsed_astats_0 @ 0x4def40] Peak level dB: -21.917938
[Parsed_astats_0 @ 0xb92180] Channel: 1
[Parsed_astats_0 @ 0xb92180] Peak level dB: -6153.053111
[Parsed_astats_0 @ 0xb92180] Overall
[Parsed_astats_0 @ 0xb92180] Peak level dB: -6153.053111
...


  


  It gets me mostly what I need if I filter out peak levels < -120db. The problem is it identifies all channels as "Channel 1". Maybe this is because each audio stream only has a single channel in it. But I find nothing in the original output to tie each "audio status section" (the part containing "Channel :" through "Sero crossings rate") to the associated stream (e.g., 0:0, 0:1, etc.). Can I reliably deduce this just based on the order of the output ?

  &#xA;

  Should I be using a different filter (instead of astats) or parameter set to get this info ?

  &#xA;

• ffmpeg video duration is not equal to duration after hls process

  9 décembre 2022, par Timur Khazhiev

  Problem

  &#xA;

  For videofile input I preprocess/encode it to libx264. Then I'm trying to cut video into 2 second chunks except last one (last one being < 2 seconds) using hls processing

  &#xA;

  ffmpeg -v error -i video.mp4 -x264-params "keyint=60:min-keyint=60:scenecut=0" 
-hls_time 2 -hls_list_size 0 -hls_segment_filename chunk%03d.ts index.m3u8


  &#xA;

  which follows this problem

  &#xA;

  then looking into index.m3u8 file reveals that sum of all chunks' durations does not add up to original video duration :

  &#xA;

  % ffprobe -loglevel quiet -print_format flat -show_entries format=duration index.m3u8     

format.duration="204.880000"

% ffprobe -loglevel quiet -print_format flat -show_entries format=duration video.mp4 

format.duration="204.892813"


  &#xA;

  Moreover duration of a chunk in index.m3u8 is not the same as in chunk file.

  &#xA;

  % ffprobe -loglevel quiet -print_format flat -show_entries format=duration chunk000.ts

format.duration="2.023222"

% cat index.m3u8
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:2
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:2.000000,
chunk000.ts
#EXTINF:2.000000,
chunk001.ts
#EXTINF:2.000000,
chunk002.ts
...


  &#xA;

  Misc

  &#xA;

  Used these videos : Me at the zoo and I finally found a useful monorail.

  &#xA;

  OS : macos Monterey 12.3.1 (21E258)

  &#xA;

  ffmpeg version 5.1.2 Copyright (c) 2000-2022 the FFmpeg developers
built with Apple clang version 14.0.0 (clang-1400.0.29.102)
configuration: --prefix=/usr/local/Cellar/ffmpeg/5.1.2 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
libavutil      57. 28.100 / 57. 28.100
libavcodec     59. 37.100 / 59. 37.100
libavformat    59. 27.100 / 59. 27.100
libavdevice    59.  7.100 / 59.  7.100
libavfilter     8. 44.100 /  8. 44.100
libswscale      6.  7.100 /  6.  7.100
libswresample   4.  7.100 /  4.  7.100
libpostproc    56.  6.100 / 56.  6.100


  &#xA;

  What I tried

  &#xA;

  &#xA;
  • Preprocess/transcode video before proceeding with hls

  &#xA;

  • Force keyframes before proceeding with hls

  &#xA;

  • Use 1, 3, 4 seconds chunks

  &#xA;

  • Use different GOP sizes

  &#xA;

  • -hls_flags split_by_time

  &#xA;

  &#xA;

  but it leads to same result or very unequal chunks

  &#xA;

  Questions

  &#xA;

  &#xA;
  1. Is it ok or I'm missing something ?

  &#xA;

  2. If not, what parameters/options should I use to force chunks to be precisely 2 seconds ?

  &#xA;

  &#xA;

• Converting video with ffmpeg from a script not in the root folder

  30 octobre 2017, par Daniel Ormerod

  I am using ffmpeg to convert videos, create thumbnails etc.

  I made the below function to convert a video and when I run it in a script in the root folder it converts ok.

  However, I am using ajax to upload the video and the script is located /ajax/upload-video.php and when I run it in that folder it fails to convert.

  I have tried sending the $src and $dest up with ../ before the filenames to go back a folder but it isn’t working.

  Can anybody help ?

  Do I need to add something to the $command line to tell it to go back a folder ?

  These are the variables being used in the function :

  $ffmpegpath = 'ffmpeg.exe';
  
  $src = 'videos/video1.wmv';
  
  $dest = 'videos/video1.mp4';

  I have tried :

  $ffmpegpath = 'ffmpeg.exe';
  
  $src = '../videos/video1.wmv';
  
  $dest = '../videos/video1.mp4';

  And the function :

  function convert_video($src, $dest) {
  
  
  
      global $ffmpegpath;
  
  
  
      if (!file_exists($src)) {
  
  
  
          echo '<p>The file does not exist</p>';
  
  
  
      } else {
  
  
  
          $command = "$ffmpegpath -i $src $dest";
  
  
  
          @exec($command, $ret);
  
  
  
          if (!file_exists($dest)) {
  
  
  
              echo '<p>The file failed to create</p>';
  
  
  
          } else {
  
  
  
              if (filesize($dest)==0) {
  
  
  
                  echo '<p>The file created but has not filesize</p>';
  
  
  
              } else {
  
  
  
                  echo '<p>File Created Successfully</p>';
  
  
  
              }
  
  
  
          }
  
  
  
      }
  
  
  
  }