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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 ?

  


• How can I read System.Drawing.Bitmaps from a video file using FFMpegCore ?

  18 avril 2021, par David Sackstein

  I am using https://github.com/rosenbjerg/FFMpegCore to write System.Drawing.Bitmaps to a video file and to read them back as bitmaps.

  


  Based on the examples I was able to implement the first step as so :

  


  public static void WriteToH264(System.Drawing.Bitmap[] bitmaps, string fileName)&#xA;{&#xA;    Directory.CreateDirectory(Path.GetDirectoryName(fileName)!);&#xA;&#xA;    WriteToH264(&#xA;        bitmaps.Select(bitmap => new BitmapVideoFrameWrapper(bitmap)),  &#xA;        4,            &#xA;        fileName);&#xA;}&#xA;&#xA;private static void WriteToH264(IEnumerable<ivideoframe> bitmaps, int frameRate, string fileName)&#xA;{&#xA;    var videoFramesSource = new RawVideoPipeSource(bitmaps)&#xA;    {&#xA;        FrameRate = frameRate&#xA;    };&#xA;  &#xA;    FFMpegArguments&#xA;        .FromPipeInput(videoFramesSource)&#xA;        .OutputToFile(fileName, true, options => options&#xA;            .WithVideoCodec(VideoCodec.LibX264))&#xA;        .ProcessSynchronously();&#xA;}&#xA;</ivideoframe>

  


  For the second part I need to implement the following function using the same library :

  


  public static System.Drawing.Bitmap[] ReadFromH264(string fileName)


  


  But I have not find an samples of how to do this.

  


  How should I implement this function ?

  


• mov : fill in subtitle dimensions after parsing tkhd

  20 mars 2014, par Michael Niedermayer

  mov : fill in subtitle dimensions after parsing tkhd
  Sample-Id : NeroRecodeSample.mp4
  

  • [DBH] libavformat/mov.c