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• Find/extract the frames which are different in two videos

  24 novembre 2022, par Greendrake

  I have two H.264 video files roughly 30GB each, with 256291 frames in each. Most, if not all, frames in the 1st video appear identical to their counterparts in the 2nd video. That said, the video content is seemingly almost (maybe completely) identical.

  


  The raw H.264 streams extracted from the video files are actually supposed to be identical but they are not : one is bigger than the other by about 2MB. So, it seems like there ought to be some differences in the picture somewhere.

  


  I have used the following command to extract a frame each 0.5s from the files and then compared the frames' md5 hashes. All 21356 frame files extracted from the first video exactly match their counterparts from the second video.

  


  for i in {0..21356} ; do ffmpeg -hide_banner -loglevel error -accurate_seek -ss `echo $i*0.5 | bc` -i video.mp4 -frames:v 1 frames/period_down_$i.bmp ; done


  


  So, the odds that the video is anyhow different are low. But not 0% chance as the one or a few different frames could just fall outside of the 0.5s picks that I tried.

  


  Is there any smart way to find/extract the diffing frames only ?

  


  I could extract all frames and compare them but that's not smart at all and would take lots of time / disk space.

  


• How to use custom function to calculate 'x' in ffmpeg crop

  17 septembre 2016, par Sasha Kastsiushkin

  ffmpeg docs have this example :

  crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(n/10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(n/7)

  To make it simpler, I will use named params and only affect output width and position x
crop=w=in_w/3:x=(in_w-out_w)/2+((in_w-out_w)/2)*sin(n/10)

  The result will be the video that is 3 times shorter than original and it will ’float’ along the x axis thanks to that sin(n/10) function. x is evaluated for each frame and n(number of the input frame) will increase and change the x position dynamically.

  I’m trying to create a custom function, which will take n or t and based on it return some value of x.

  Please help me or perhaps this is not possible. I was trying to create a small bash script, which will do so unsuccessfully.

  Thank you

• FFMpegCore .Net cuts off the fist few ( 1.5) seconds of audio

  28 mai 2024, par Tim

  I want to use FFMpegCore to convert some audio files to raw pcm. I noticed that this always cuts off 1.5 seconds of my audio from the start. I check my input stream, saved it to HD all good. If use it from cli with the same arguments everything seem fine. I tried -ss 0, no luck. This behavior is observed with .wav (RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 44100 Hz), same issue with different sample rate. I tested mp3 works fine.

  


  public async Task<memorystream> ConvertToPcmStreamAsync(Stream inputStream)&#xA;{&#xA;    var outputStream = new MemoryStream();&#xA;    &#xA;    var audioInput = new StreamPipeSource(inputStream);&#xA;    var audioOutput = new StreamPipeSink(outputStream);&#xA;&#xA;    await FFMpegArguments&#xA;        .FromPipeInput(audioInput)&#xA;        .OutputToPipe(audioOutput, options => options&#xA;            .WithCustomArgument("-ss 0 -f s16le -acodec pcm_s16le -ac 1"))&#xA;        .ProcessAsynchronously();&#xA;&#xA;    // Reset the position of the memory stream to the beginning&#xA;    outputStream.Position = 0;&#xA;&#xA;    return outputStream;&#xA;}&#xA;</memorystream>