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I am trying to pass audio and video files into FFMPEG and determine if their audio is entirely silent (I don't need to detect if the audio stream is present or not, just if it is silent), and ideally return a boolean at the end of it all, or a 0/1. I am able to output the silence information via:

ffmpeg -i FILE.mov -af silencedetect=noise=0.0001 -f null - 2>&1

I think I would need to check if the last silence_duration value is equal to the duration.

There seems to be different rounding of decimal points depending on the values for FFMPEG's output (duration = 15.67, silence_duration=15.6667), so whatever accuracy is possible given these circumstances is ok.

I'm not sure how to parse the output in order to do this and any nudges in the right direction would be extremely helpful - Thanks!

Here are two possible examples that contain silence:

Entirely Silent File

ffmpeg version 4.4.1 Copyright (c) 2000-2021 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.29)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.4.1_3 --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-avresample --enable-videotoolbox
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/user/Desktop/SilenceAll.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 1
    compatible_brands: qt  
    creation_time   : 2021-11-23T16:08:58.000000Z
    timecode        : 01:00:00:09
  Duration: 00:00:15.67, start: 0.000000, bitrate: 11795 kb/s
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 8955 kb/s, 30 fps, 30 tbr, 3k tbn, 60 tbc (default)
    Metadata:
      handler_name    : Video Handler
      vendor_id       : [0][0][0][0]
      encoder         : H.264
  Stream #0:1(und): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, stereo, s32 (24 bit), 2304 kb/s (default)
    Metadata:
      handler_name    : Sound Handler
      vendor_id       : [0][0][0][0]
  Stream #0:2(und): Data: none (tmcd / 0x64636D74), 0 kb/s (default)
    Metadata:
      handler_name    : Timecode Handler
      timecode        : 01:00:00:09
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> wrapped_avframe (native))
  Stream #0:1 -> #0:1 (pcm_s24le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, null, to 'pipe:':
  Metadata:
    major_brand     : qt  
    minor_version   : 1
    compatible_brands: qt  
    timecode        : 01:00:00:09
    encoder         : Lavf58.76.100
  Stream #0:0(und): Video: wrapped_avframe, yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 30 fps, 30 tbn (default)
    Metadata:
      handler_name    : Video Handler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc58.134.100 wrapped_avframe
  Stream #0:1(und): Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s (default)
    Metadata:
      handler_name    : Sound Handler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc58.134.100 pcm_s16le
[silencedetect @ 0x7f93de904280] silence_start: 0.49 bitrate=N/A speed=11.7x    
frame=  470 fps=0.0 q=-0.0 Lsize=N/A time=00:00:15.66 bitrate=N/A speed=31.7x    
video:246kB audio:2938kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[silencedetect @ 0x7f93de904280] silence_end: 15.6667 | silence_duration: 15.6667

Silent at the Begging and End of File (Two sections of silence, but not entirely silent)

ffmpeg version 4.4.1 Copyright (c) 2000-2021 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.29)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.4.1_3 --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-avresample --enable-videotoolbox
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/user/Desktop/SilenceTopTail.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 1
    compatible_brands: qt  
    creation_time   : 2021-11-23T16:09:32.000000Z
    timecode        : 01:00:00:09
  Duration: 00:00:15.67, start: 0.000000, bitrate: 11795 kb/s
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 8955 kb/s, 30 fps, 30 tbr, 3k tbn, 60 tbc (default)
    Metadata:
      handler_name    : Video Handler
      vendor_id       : [0][0][0][0]
      encoder         : H.264
  Stream #0:1(und): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, stereo, s32 (24 bit), 2304 kb/s (default)
    Metadata:
      handler_name    : Sound Handler
      vendor_id       : [0][0][0][0]
  Stream #0:2(und): Data: none (tmcd / 0x64636D74), 0 kb/s (default)
    Metadata:
      handler_name    : Timecode Handler
      timecode        : 01:00:00:09
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> wrapped_avframe (native))
  Stream #0:1 -> #0:1 (pcm_s24le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, null, to 'pipe:':
  Metadata:
    major_brand     : qt  
    minor_version   : 1
    compatible_brands: qt  
    timecode        : 01:00:00:09
    encoder         : Lavf58.76.100
  Stream #0:0(und): Video: wrapped_avframe, yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 30 fps, 30 tbn (default)
    Metadata:
      handler_name    : Video Handler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc58.134.100 wrapped_avframe
  Stream #0:1(und): Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s (default)
    Metadata:
      handler_name    : Sound Handler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc58.134.100 pcm_s16le
[silencedetect @ 0x7fb140d0d100] silence_start: 0.49 bitrate=N/A speed=12.8x    
[silencedetect @ 0x7fb140d0d100] silence_end: 5.16667 | silence_duration: 5.16667
[silencedetect @ 0x7fb140d0d100] silence_start: 10.1
frame=  470 fps=0.0 q=-0.0 Lsize=N/A time=00:00:15.66 bitrate=N/A speed=31.9x    
video:246kB audio:2938kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[silencedetect @ 0x7fb140d0d100] silence_end: 15.6667 | silence_duration: 5.56667
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3 Answers 3

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2

You can pipe the output of ffmpeg through awk for further processing:

ffmpeg ... | awk '/silence_end/ && ($5 == $8) {print "silent"}'

I didn't bother to check silence_start because for the whole audio to be silent, silent_end needs to match silence_duration anyway.

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5
  • Thanks for the response @nohillside! It seems my assumption about the output was not correct. Unfortunately, the silence_duration just outputs the silence duration for whatever the section of silence it has detected, so if there are multiple sections of silence, with the end of the file containing the last piece of detected silence (begginning >middle>end where it is silent>not silent>silent), then this sort of parsing would still 'think' that the file is silent. I've edited my post to be more compreshensive and I’ve included the entire output of the commands for both scenarios. Thanks again!
    – Darbis
    Nov 23, 2021 at 16:25
  • @Darbis Thanks for the updated output. Not sure I understand the math though, silence_end - silence_start isn't equal to silence_duration. It would be possible to find out whether there is a time gap between the slices in case there are several, would this be good enough?
    – nohillside ♦
    Nov 23, 2021 at 16:38
  • Thanks @nohillside. I guess the math would be something like "if sum of all silence_duration items equals duration of file, then file is silent. Else file is not silent". Also, I guess if the file was entirely silent, there would only be one silencedetect entry and its value for silence_duration would be the same length as the duration (not the silence_duration, but file duration which is up higher in the output as "Duration"), so alternatively the math could be "If the last entry of silence_duration is equal to Duration then file is silent". That making more sense? Thanks again!
    – Darbis
    Nov 23, 2021 at 17:23
  • @Darbis Sure it does. But if you look at your second example the math of the slices itself doesn't work: the first slice starts at 0.49 and ends at 5.16667, yet the duration is 5.16667 as well (similar for the second slice). And the duration itself is 15.67 while the last slice ends at 15.6667. Sure, we can round off the values etc but it gets tricky quickly
    – nohillside ♦
    Nov 23, 2021 at 19:10
  • Thanks @nohillside. Yeah, I'm not sure why FFMPEG reports the first slice as beginning at 0.49. I've tried with multiple different files and there doesn't seem to be consistency in what I've found. Would a modified version of my last logic idea work instead: "If everything before the "." in the last entry of silence_duration is equal to the Duration in seconds then the file is silent. Else not silent" Because Duration is output as HH:MM:SS.MS and silence_duration is output as SS.MS (regardless of how long the file is it is always in seconds). This would give a resolution of 1 second. Thanks!
    – Darbis
    Nov 23, 2021 at 19:58
1

Another way to check if it is a silence file is to use peak detection.

If the file has no peaks, ffmpeg will output the peak as "-inf".

ffmpeg -i input.ogg -af ebur128=peak=true -f null -

outputs:

  Integrated loudness:
    I:         -70.0 LUFS
    Threshold:   0.0 LUFS

  Loudness range:
    LRA:         0.0 LU
    Threshold:   0.0 LUFS
    LRA low:     0.0 LUFS
    LRA high:    0.0 LUFS

  True peak:
    Peak:       -inf dBFS

By outputting -inf, it has no peaks.

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0
0

The last line of ffmpeg output includes size information for each track of an mp4. If your silence is actual silence (and not a quiet hiss or something), you could also consider checking if the file has 0kb of audio.

$ ffmpeg -i silentvideo.mp4 -f null -

...

video:271kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

We can grep for that, so here's a one-liner that will print NO AUDIO (0) or HAS AUDIO (1).

ffmpeg -I silentvideo.mp4 -f null - 2>&1 | grep -q "audio:0kB" && echo "NO AUDIO (0)" || echo "HAS AUDIO (1)"

$ ffmpeg -i silentvideo.mp4 -f null - 2>&1 | grep -q "audio:0kB" && echo "NO AUDIO (0)" || echo "HAS AUDIO (1)"
NO AUDIO (0)
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