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• How to scale watermark in percent with ffmpeg ? [duplicate]

  31 décembre 2015, par user3390767

  This question already has an answer here :

  • How to scale and position watermark to scale ?
    
    1 answer
    

  I run a video site, but watermark logo still in different sizes in every video with different resolution.
  My question : is there a way to scale watermark image in every video by some kind of percentage ?
  I use next command :

  /usr/bin/ffmpeg -i video_in.mp4 -f mp4 -vcodec libx264 -r 30 -movflags
  faststart -profile:v baseline -vf "movie=logo.png, scale=200:37
  [watermark] ; [in][watermark] overlay=10:10 [out]" -s 640x360 -acodec
  libfaac -ab 128k -ar 44100 video_out.mp4

  So as you see the scale of watermark is static, but I want to make it dynamic. Is there way to do this in percentage by depending of video resolution ?

  Cheers !

• FFmpeg massive data loss when writing large data and swapping segments

  25 avril 2023, par Bohdan Petrenko

  I have an ffmpeg process running which continiously writes audio data to two 30 seconds (for testing, I'm actually planning to use 5 minutes) segments. The problem is that when I write some audio data with length more than size of two segments (60 seconds), 8-17 seconds of audio is lost. Here is how I run FFmpeg and write data :

  


      _ffmpeg = Process.Start(new ProcessStartInfo
    {
        FileName = "ffmpeg",
        Arguments = 
            $"-y -f s16le -ar 48000 -ac {Channels} -i pipe:0 -c:a libmp3lame -f segment -segment_time {BufferDuration} -segment_format mp3 -segment_wrap 2 -reset_timestamps 1 -segment_list \"{_segmentListPath}\" \"{segmentName}\"",
        UseShellExecute = false,
        RedirectStandardInput = true
    })!;
    // Channels is usually 1, BufferDuration is 30


  


  And here is how I write data :

  


  public async Task WriteSilenceAsync(int amount)
{
    if (amount > _size) amount = _size; // _size is 48000 * 1 * 2 * 30 * 2 = 5760000 (size of 1 minute of audio)
    
    var silence = _silenceBuffer.AsMemory(0, amount);
    await _ffmpeg.StandardInput.BaseStream.WriteAsync(silence);
}


  


  I tried to change the ffmpeg parameters and ways I write data. But I haven't found the solution.

  


  I'm sure that the problem is caused by ffmpeg segments, because if I disable segmenting and write audio to a single file, there are no problems with data loss or audio missmatch. I also sure that amount of silence to add in WriteSilenceAsync() method is calculated right. I'm not sure if the problem appears with data length more than 30 seconds but less then 1 minute, but I think it doesn't.

  


  I don't know how to solve this problem and would be glad to see any suggestions or solutions.

  


• Aligning multiple words vertically with drawtext & ffmpeg

  26 mai 2023, par CRAIG

  I am needing to vertically align several drawtext chained commands that are of various font sizes off of a center point, but in a way where similar fonts/sizes will appear to be correctly aligned off of their baselines.

  


  The $centerline is a vertical top positioned line that theoretically is the vertical center that each text would sit upon regardless of total text height/font size so even differing fonts of differing sizes will look good together.

  


  But the max_glyph_a is to ensure that the same fonts with the same font size will sit on the same baseline. I would think this would do it, but no, it's off vertically.

  


   $y = '(' . $centerline . '+(text_h/2)-max_glyph_a)';


  


  I can't wrap my noggin around this. Any ideas ?