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• FFmpeg Negative Duration [migrated]

  22 septembre 2014, par filby

  i have a large number of small videos (parts of a larger) of the form :

  Metadata:
  
  major_brand     : isom
  
  minor_version   : 512
  
  compatible_brands: isomiso2avc1mp41
  
  encoder         : Lavf55.43.100
  
  Duration: 00:00:05.53, start: -1.831497, bitrate: 3355 kb/s
  
  Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 4760 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
  
  Metadata:
  
    handler_name    : VideoHandler
  
  Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 157 kb/s (default)
  
  Metadata:
  
    handler_name    : SoundHandler

  I want to completely discard the negative start, the 1.83 seconds, and keep only the 3.67 seconds in the positive ’axis’.

  I cut the videos with the correct duration however i believe due to some sync i did in sound (in the original), resulted in me having a video of 5.53 second, of which 1.83 is audio only, and the last 3.67 seconds are the ones i want to keep (and the ones i did cut).

  In a video player i can watch the 3.67 seconds i want to however if i extract the audio i get +1.83 seconds of audio at start from the original video (from which i cut the parts) which i didnt intend to cut. What can i do ;

  P.S.
  Example of the command i used to cut the part :

  ffmpeg -ss 818 -i input -t 3.67 -codec:v libx264 -profile:v high -preset slow -b:v 5000k -maxrate 5000k -threads 0 -codec:a copy output

• How can I split a bunch of m4a files in chunks and replace their metadata with ffmpeg ?

  28 novembre 2018, par adrifromhh

  I read through a lot of threads that adressed my issue partially and tried to write a script that splits an .m4a audiofile in parts and replaces its metadata.

  I didn’t manage to achieve this in a single line (Maybe you can tell me how to) but came pretty close with these two scripts. (I split them in two just for readability and debugging.)

  #!/bin/bash
  
  # cutaudio.sh
  
  
  
  input=$1
  
  output=$2
  
  duration=$3
  
  
  
  ffmpeg -i $input -map 0 -f segment -segment_time $duration -c copy "$output-%03d.m4a"

  The above script works fine and splits the files in chunks of the provided length.

  #! /bin/bash
  
  # stripmetadata.sh
  
  
  
  
  
  input=$1
  
  
  
  n="1"
  
  for i in $input*; do 
  
      title="Part $n"
  
      ffmpeg -i $i -map 0 -metadata title="$title" -c copy -y "$i"
  
      n=$((n + 1))
  
  done

  This script actually manages to replace the title in the metadata, however the files are also being stripped to the first second. They’re all 33,7 kb in size after the second script. I am still new to ffmpeg so help would be appreciated a lot !

  Edit :
  Here’s the resulting script, for anyone interested :
  https://github.com/adrifromhh/cutaudio
  I use it to cut downloaded Audiobooks (from youtube or recorded from Audible) in usable parts.

• How to mimic Audacity's "truncate silence" with ffmpeg "silenceremove" filter

  16 juin 2024, par Cara Duf

  I want to remove completely silence parts from wav files with ffmpeg.

  


  Input wav can be like :


  


  I am using the following ffmpeg command to remove silence part ffmpeg -i input.wav -af silenceremove=stop_periods=-1:stop_duration=0.2:stop_threshold=-45dB output.wav because I understand from the doc that it will remove all silence parts longer than 0.2 s (silence being below -45dB).

  


  But I get that where silence part has only been reduced to around 0.1 wheras I want it to be 0 (no remaining silence).

  


  In Audacity I will use "truncate audio" filter and choose the above parameters to detect silence and in the action part I will choose to truncate to 0 : .

  


  This will yield to what I want (ie an audio with no silence part remaining) :


  


  Searching on the internet only lead me to what I already do.

  


  So how can I reproduce the output I get from Audacity "Truncate Silence" filter with ffmpeg and remove all silence parts from audio ?

  


  Edit : The output from silencedetect filter is correct : ffmpeg -i input.wav -af silencedetect=0.2:n=-45dB -f null - detects exactly what audacity detects.

  


  Thanks in advance for your help