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• How to use sexagesimal syntax in arguments of FFmpeg or if impossible how to convert it in Windows CMD shell

  6 décembre 2020, par Link-akro

  Question updated 2020-12-06 to enlarge the scope without discarding the prior answer which applies to both prior and larger cases.

  


  I had trouble to provide a sexagesimal time (HH:MM:SS.mm) to a filter option that was not an expression. For instance trim filter.
It happens there is an escaping rule i did not know yet when i first asked, and was addressed in the first comment by @Gyan.

  


  The problem is universal, but the solution may depend on the shell if we go the scripting route... and i am currently stuck with Windows's CMD.exe.

  


  For instance the following skips one minute and 4 tenths of seconds in all streams as accurately as it can seek each, then invokes the trim filter to keep the segment between one and two minutes of the remaining duration, and do so with two different syntaxes. This example happens to be compatible with both CMD and BASH shells so no escaping hell.

  


  ffmpeg -ss "1:00.4" -i INPUT -vf "trim=start='1\:00':end='120'" OUTPUT


  


  Then how do we achieve the same in the expressions within the filters ?
If we cannot avoid using the scripting of the shell, i am looking for a Windows CMD solution.
I had posted one answer with a piece of script to convert a textual sexagesimal time to a textual decimal fractional time in seconds, which was not useful for the original case, but may apply to more generic cases and in particular to the expressions.

  


  Example of failed attempt with one expression in the select filter.

  


  ffmpeg -ss "1:00.4" -i INPUT -vf "select='between(t,1\:00',120)'" OUTPUT


  


  The sexagesimal notation seems to not be supported by ffmpeg filter expressions as i found no reference of it in the documentation nor in SO/web.

  


  I browsed through the list of functions defined in ffmpeg expression library but did not find any way to parse the sexagesimal input there yet, nor any way to use text in its semantics.

  


  However i found some unrelated example that hard-coded some arithmetical expression to provide the numerical decimal amount of seconds equivalent to what was intended, such as 2*60+2 to mean 2:02.

  


  The polynome used above to compute seconds may use preprocessing of shell variable, whichever shell it is, but we need to parse the components of HH:MM:SS.mm to put them in those variable first. You know, using bash $var or cmd %var%/%~1 styles. Otherwise we may compute the polynome completely in the shell instead of the expression but it is so much trouble for little gain.

  


  So while CMD still exists like an undead and becomes really dead , and while i do not have the opportunity yet to replace it, i wish for an answer that either :

  


  

  • does not need the shell/script at all, OR

  


  • provide a solution in Windows CMD, although relying on it as little as possible.

  


  


  Reminder and clarification, the use case assumes that we are given a textual sexagesimal time as input and intend to use it in an expression of ffmpeg filter with as little shell dependency as possible or otherwise satisfy Windows CMD.

  


• Using FFMPEG : How to do a Scene Change Detection by audio

  9 janvier 2021, par dantedel

  I have a video that has many scenes, within each scene there are several video cuts with and single unique narator.
I'm trying to split the video to individual scenes based on narator. So far only found only a way using select/scene to get timestamps based on scene video changes.

  


  Using FFMPEG : How to do a Scene Change Detection ? with timecode ?

  


  ffmpeg -i input.flv  \
       -filter:v "select='gt(scene,0.4)',showinfo" \
       -f null \
       - 2> ffout


  


  Is there an equivalent way to get the scene changes by examining changes in audio ?

  


• Blown-out speaker ffmpeg sound effect

  8 février 2021, par Shalin Shah

  I was wondering how to do the blown-out speaker effect using ffmpeg where the audio just sounds completely destroyed.

  


  I've tried a bunch of combinations of different commands on ffmpeg and the closest I've gotten is the following (where I use the superequalizer and then make the volume super high) :

  


  import ffmpeg
(
    ffmpeg
    .input('shark.wav')
    .filter("superequalizer", 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20)
    .filter("volume", 10)
    .output('output_speaker.wav')
    .run()
)


  


  I'm using a python wrapper but here's the command line equivalent :

  


  ffmpeg -i shark.wav -af "superequalizer=1b=20:2b=20:3b=20:4b=20:5b=20:6b=20:7b=20:8b=20:9b=20:10b=20:11b=20:12b=20:13b=20:14b=20:15b=20:16b=20:17b=20:18b=20,volume=10" output_speaker.wav


  


  The problem with the above is that it doesn't do anything for files that aren't already super loud (such as recorded audio) and most of the time the audio actually just ends up clipping and then being super soft.

  


  Does anyone have suggestions on how to do this effect ? Thanks !