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• 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.

  


• SVT-AV1 : After encoding the video seeking is very bad in any video player (even HTML5)

  18 juin 2020, par Viktor Machnik

  i am using SVT-AV1 and FFMPEG to encode Videos into the AV1 video and opus audio codec (.webm), it works fine, except that the video seeking do not work really (extremly bad). When i seek, the CPU useage jumps up and it takes up to minutes until the seeking process finishes.

  



  Here is how i encode the videos :

  



  

  1. Convert any video into yuv : ffmpeg -i  -preset veryslow -level 6.2 .yuv

  


  2. First AV1 run svt-av1 -i '.yuv' -w  -h  --fps  --rc 0 -q 30 --preset 8 -b '.\output1.ivf' --output-stat-file '.\stat_file.stat' --keyint 1 --enable-restoration-filtering 1

  


  3. Second AV1 run svt-av1 -i '.yuv' -w  -h  --fps  --rc 0 -q 30 --preset 3 -b '.\output.ivf' --input-stat-file '.\stat_file.stat' --keyint 1 --enable-restoration-filtering 1

  


  4. Get source video audio in opus codec ffmpeg -i  -c:a libopus -vn -preset veryslow -level 6.2 output.ogg

  


  5. Get final .webm video ffmpeg -i output.ivf -i output.ogg -c copy output.webm

  


  



  I have allready tryed to play with the —keyin option, also just letting it away and use the encoder default, but the results are always the same. (--keyin 1 seems to work better than without this option, but also very very bad)

  



  What am i doing wrong ?

  



  Extras : I am using Windows 10 with downloaded version of SVT-AV1 and FFMPEG (I just renamed the SVT-AV1 Encoder .exe file to be svt-av1.exe). Used CPU is Ryzen 9 3900X

  


• Adding transparency to a video from black and white (and gray) alpha information video images

  3 juillet 2018, par Jan F.

  I’d like to create a video with transparency (and semi transparency) in android. The images of the source video are split into two images, the top one with color information (looks like the normal video image), the bottom one with alpha information (the same shapes but only in black and white and gray, black means transparent).

  This is the solution for iOS :
  https://medium.com/@quentinfasquel/ios-transparent-video-with-coreimage-52cfb2544d54

  What would be the best way to to this in android ?

  Can this be solved with javacv, FFmpegFrameGrabber, FFmpegFrameFilter etc.?

  Or better with OpenGL ES and shaders ?

  Are there any samples ?

  Thanks !