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• ffmpeg : Apply a time-based expression to control lowpass, highpass, aphaser, or aecho [closed]

  17 mai 2024, par Wes Modes

  I am constructing complexFilters to procedurally generate audio with ffmpeg via fluent-ffmpeg. The interesting part of my fluent-ffmpeg complex filters look like :

  


  {
   "filter": "volume",
   "options": {
       "volume": "min(1, max(0, ((cos(PI * t * 1 / 13) * 1 + cos(PI * t * 1 / 7) * 0.5 + cos(PI * t * 1 / 3) * 0.25) +
-0.5 ) * 0.75 * -1 + 0.5))",
       "eval": "frame"
    },
    "inputs": "track_1_output",
    "outputs": "track_1_adjusted"
},


  


  Note that I am using an expression to determine the volume dynamically. To simplify my tests, I'm constructing complexFilters on the command line to understand the mysteries of some of the lightly-documented ffmpeg filters. Here's a working CLI test of using the volume filter to fade the sources in and out according to a time-based expresssion :

  


  # working fade in/out
ffmpeg -i knox.mp3 -i static.mp3 -filter_complex \
"[0:a] \
    volume = 'min(1, max(0, 0.5 + 0.5 * cos(PI * t / 5)))': eval=frame \
    [a0]; \
[1:a] \
    volume = 'min(1, max(0, 0.5 - 0.5 * cos(PI * t / 5)))': eval=frame \
    [a1]; \
[a0][a1]
    amix = inputs=2: duration=shortest" \
-c:a libmp3lame -q:a 2 output.mp3


  


  Now I want to apply lowpass, highpass, aphaser, and/or aecho to the transitions using a time-based expression. For instance, looking at lowpasss, according to ffmpeg -filters it says that it has time-based support :

  


    T.. = Timeline support
 TSC lowpass           A->A       Apply a low-pass filter with 3dB point frequency.


  


  How can I similarly apply a time-based expression to lowpass, highpass, aphaser, or aecho ? I thought the mix option might be the key, but I couldn't construct a working example and couldn't find any examples.

  


  # applying a lowpass filter
ffmpeg -i knox.mp3 -filter_complex \
"[0:a] \
    lowpass=f=3000:mix='0.5 + 0.5 * cos(PI * t / 5)';" \
-c:a libmp3lame -q:a 2 output.mp3


  


  Or if you prefer the fluent-ffmpeg filter :

  


  const ffmpeg = require('fluent-ffmpeg');

ffmpeg('knox.mp3')
    .complexFilter([
        {
            filter: 'lowpass',
            options: {
                f: 3000,
                mix: '0.5 + 0.5 * cos(PI * t / 5)'
            },
            inputs: '[0:a]',
        }
    ])
    .audioCodec('libmp3lame')
    .audioQuality(2)
    .save('output.mp3')
    .on('end', () => {
        console.log('Processing finished successfully');
    })
    .on('error', (err) => {
        console.error('Error: ' + err.message);
    });


  


  With the resultant error :

  


  [Parsed_lowpass_1 @ 0x7f9a72005c00] [Eval @ 0x7ff7bec423d8] Undefined constant or missing '(' in 't/5)'
[Parsed_lowpass_1 @ 0x7f9a72005c00] Unable to parse option value "0.5 + 0.5 * cos(PI * t / 5)"
Error applying option 'mix' to filter 'lowpass': Invalid argument


  


  What complicated fffmpeg faerie magic is needed to make some of the filters other than volume controlled by a time-based expr ?

  


• When converting a PNG with transparency to AVIF with FFmpeg, the transparency is lost [closed]

  24 novembre 2023, par Rodrigo

  I have the following script that converts all PNGs to AVIF in the current directory.

  


  #!/bin/zsh

setopt nullglob

for file in *.png; do
  filename="${file%.*}"
  
  ffmpeg -i "$file" -c:v libaom-av1 -pix_fmt yuva420p -lossless 1 -metadata:s:v:0 rotate="" "${filename}.avif"
done

unsetopt nullglob


  


  When converting, the alpha channel is lost. How can this be adjusted, is there a specific parameter ?

  


  Original image

  


  

  


  AVIF image

  


  

  


• openCV 2.4.10 lost cinepak radius codec

  28 octobre 2014, par user3652747

  I am working on a Windows 7 64 bit platform.

  Before :
  I was using OpenCV 2.4.6, compiled by myself with CodeBlocks and a MinGW compiler. When recording a video, I was able to select the Cinepak Radius Codec (CVID) and all my world was shinny. I don’t remember tweaking a lot the configuration of CMAKE when creating the CodeBlocks project to compile OpenCV.

  Now :
  I download the last stable version OpenCV 2.4.10 and I have to use this one. So I applied the same recipe : CMAKE, CodeBlocks project, compile. But then I cannot choose the Cinepak Radius Coded while creating a new video.

  Questions :
  Did the Codec disappears from OpenCV or did I miss one flag in the CMAKE configuration ?

  Of course I tried other config, but to me, I just had to activate WITH_FFMPEG and WITH_VFW flags. Do you have any tips on that ?

  Thanks !