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• Script to cut video by silence part with FFMPEG

  11 février 2020, par fricadelle

  This is a question that is raised here How to split video or audio by silent parts or here How can I split an mp4 video with ffmpeg every time the volume is zero ?

  So I was able to come up with a straightforward bash script that works on my Mac.

  Here it is (only argument is the name of the video to be cut, it will generate a file start_timestamps.txt with the list of silence starts if the file does not exist and reuse it otherwise) :

  #!/bin/bash
  
  
  
  INPUT=$1
  
  
  
  filename=$(basename -- "$INPUT")
  
  extension="${filename##*.}"
  
  filename="${filename%.*}"
  
  
  
  SILENCE_DETECT="silence_detect_logs.txt"
  
  TIMESTAMPS="start_timestamps.txt"
  
  
  
  if [ ! -f $TIMESTAMPS ]; then
  
      echo "Probing start timestamps"
  
      ffmpeg -i "$INPUT" -af "silencedetect=n=-50dB:d=3" -f null - 2> "$SILENCE_DETECT"
  
      cat "$SILENCE_DETECT"| grep "silence_start: [0-9.]*" -o| grep -E '[0-9]+(?:\.[0-9]*)?' -o > "$TIMESTAMPS"
  
  fi
  
  
  
  PREV=0.0
  
  number=0
  
  
  
  cat "$TIMESTAMPS"| ( while read ts
  
  do
  
      printf -v fname -- "$filename-%02d.$extension" "$(( ++number ))"
  
      DURATION=$( bc <<< "$ts - $PREV")
  
      ffmpeg -y -ss "$PREV" -i "$INPUT" -t "$DURATION" -c copy "$fname"
  
      PREV=$ts
  
  done
  
  printf -v fname -- "$filename-%02d.$extension" "$(( ++number ))"
  
  ffmpeg -y -ss "$PREV" -i "$INPUT" -c copy "$fname" )

  Unfortunately it does not seem to work :

  I have a video that is basically a collection of clips, each clip being introduced by a 5 second silence with a static frame with a title on it. So I want to cut the original video so that each chunk is the 5 seconds "introduction" + video until the next introduction. Hope it’s clear.

  Anyway, in my script I first find all silence_start using ffmpeg silencedetect plugin. I get a start_timestamps.txt that read :

  141.126
  
  350.107
  
  1016.07
  
  etc.

  Then for example I would call (I don’t need to transcode again the video), knowing that (1016.07 - 350.107) = 665.963

  ffmpeg -ss 350.107 -i Some_video.mp4 -t 665.963 -c copy "Some_video02.mp4"

  The edge cases being the first chunk that has to go from 0 to 141.126 and the last chunk that has to go from last timestamp to end of the video.

  Anyway the start_timestamps seem legit. But my output chunks are completely wrong. Sometimes the video does not even play anymore in Quicktime. I don’t even have my static frame with the title in any of the videos...

  Hope someone can help. Thanks.

  EDIT Ok as explained in the comments, if I echo $PREV while commenting out the ffmpeg command I get a perfectly legit list of values :

  0.0
  
  141.126
  
  350.107
  
  1016.07
  
  etc.

  With the ffmpeg command I get :

  0.0
  
  141.126
  
  50.107
  
  016.07
  
  etc.

  bash variable changes in loop with ffmpeg shows why.

  I just need to append < /dev/null to the ffmpeg command or add -nostdin argument. Thanks everybody.

• How do you generate a looping animated gif for Facebook with ffmpeg

  7 février 2020, par Alan W. Smith

  When I paste a giphy url (like this one) into a facebook post or comment, the gif plays immediately and loops indefinitely. When I upload ones I make from ffmpeg, neither of those things happen. You have to click a play button to start the animation and then it ends after one time through.

  I have a couple of ffmpeg commands I use to create the gifs. They are :

  ffmpeg -ss 10 -t 5  -i input.m4v -vf "fps=15,scale=800:-2:flags=lanczos,palettegen" -y palette.png

  and

  ffmpeg -ss 10.6 -t 5 -i input.m4v -i palette.png -filter_complex "fps=15,scale=800:-1:lanczos[video];[video][1:v]paletteuse" output.gif

  The first one generates a custom color pallet that’s used by the second one to create a high quality animated gif. I’ve also tried adding -loop 0 (i.e. ffmpeg -ss 10.6 -t 5 -i input.m4v -i palette.png -filter_complex "fps=15,scale=800:-1:lanczos[video];[video][1:v]paletteuse" -loop 0 output.gif) but that didn’t work either.

  I also tried uploading the ffmpeg generated images to a personal website and calling them from there but those didn’t load at all.

  In case it helps, here’s a copy of one of the gifs (which autostarts and loops on StackOverflow for me but not on FB)

  

  How does one go about creating a gif that will autostart and loop indefinitely for facebook ?

  (Note : I’ve got no problem if I need to do something with a personal website, but I don’t want to use Giphly or the other animated gif sites directly if at all possible. Also worth pointing out that I discovered if I download the image from giphly and upload it, it doesn’t autostart either. So, this may be something internal to FB, but I’d still like to figure that out.)

• Command line ffmpeg, to insert part of a mp3 audio to another file

  14 janvier 2020, par tgkprog

  Want to copy from 3rd second of b.mp3 till 2:05 seconds of b.mp3 and append to the end of a.mp3 (its 3:23 long).

  Command :

  ffmpeg -i a.mp3 -i b.mp3

  Output :

  ffmpeg version 4.0.4-0ubuntu1 Copyright (c) 2000-2019 the FFmpeg developers   built with gcc 8 (Ubuntu 8.2.0-7ubuntu1)
  
    configuration: --prefix=/usr --extra-version=0ubuntu1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      56. 14.100 / 56. 14.100
  
    libavcodec     58. 18.100 / 58. 18.100
  
    libavformat    58. 12.100 / 58. 12.100
  
    libavdevice    58.  3.100 / 58.  3.100
  
    libavfilter     7. 16.100 /  7. 16.100
  
    libavresample   4.  0.  0 /  4.  0.  0
  
    libswscale      5.  1.100 /  5.  1.100
  
    libswresample   3.  1.100 /  3.  1.100
  
    libpostproc    55.  1.100 / 55.  1.100
  
  Input #0, mp3, from 'a.mp3':
  
    Metadata:
  
      encoder         : Lavf58.12.100
  
    Duration: 00:02:48.00, start: 0.011021, bitrate: 144 kb/s
  
      Stream #0:0: Audio: mp3, 48000 Hz, stereo, fltp, 144 kb/s
  
      Metadata:
  
        encoder         : Lavc58.18
  
  Input #1, mp3, from 'b.mp3':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2mp41
  
      encoder         : Lavf58.12.100
  
    Duration: 00:01:33.02, start: 0.011995, bitrate: 117 kb/s
  
      Stream #1:0: Audio: mp3, 44100 Hz, stereo, fltp, 117 kb/s
  
      Metadata:
  
        encoder         : Lavc58.18
  
  At least one output file must be specified