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• avfilter/vf_idet : Fixing idet for single-frame inputs.

  28 novembre 2014, par Neil Birkbeck

  avfilter/vf_idet : Fixing idet for single-frame inputs.
  Handle single frame inputs similar to yadif (e.g., https://github.com/FFmpeg/FFmpeg/commit/0f9f24c9cfd291c7ece4d3bad64fdf06d107168a and https://github.com/FFmpeg/FFmpeg/commit/681e008d06d2241d50abe6316c908a184ddc5942)
  Example :
  
    ffmpeg -r 1 -t 1 -i fate-suite/ffmpeg-synthetic/vsynth1/%02d.pgm  -vf idet,showinfo -f null -y /dev/null
  Previously :
  
    Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)
  
    [Parsed_idet_0 @ 0x36389d0] Repeated Fields : Neither :     0 Top :     0 Bottom :     0
  After patch :
  
    [Parsed_showinfo_1 @ 0x1909810] n:0 pts:0 pts_time:0 pos :-1 fmt:gray sar:0/1 s:352x432 ...
  
    [Parsed_idet_0 @ 0x18f9bb0] Repeated Fields : Neither :     1 Top :     0 Bottom :     0
  Fate looks good.
  Signed-off-by : Neil Birkbeck <neil.birkbeck@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavfilter/vf_idet.c

• what random function the ffmpeg filter expression called ?

  8 octobre 2020, par Wang

  for example this random(-1) in geq :

  


  ffmpeg -f lavfi -i nullsrc=s=10x10:r=25:d=4 -vf geq=lum='255':cb='255*random(-1)':cr='255*random(-1)',scale=200:200:flags=neighbor -bf 0 test.mp4


  


  I always get exactly the same color of first 2 pixels in the first frame. And the first frame always has very similar colors. Star from 3rd frame its start to getting better. Moreover, the random() seems only introduce random inside single frame. The sequence of first pixel of each frame is exactly the same :

  


  ffmpeg -f lavfi -i nullsrc=s=1x1:r=25:d=4 -vf geq=lum=255:cb='255*random(-1)':cr='255*random(-1)',scale=10:10:flags=neighbor -vframes 10 f%05d.png


  


  

  


  

  


  I looked into source code, but I cannot see what random function actually get called :

  


          case e_random:{
            int idx= av_clip(eval_expr(p, e->param[0]), 0, VARS-1);
            uint64_t r= isnan(p->var[idx]) ? 0 : p->var[idx];
            r= r*1664525+1013904223;
            p->var[idx]= r;
            return e->value * (r * (1.0/UINT64_MAX));
        }



  


  How do I suppose to get proper randomness in the geq ?

  


• Fix motion blur in still frames from mpeg2video

  14 mars 2017, par Bird

  I’m extracting still frames from a video using the basic code :

  ffmpeg -i video.MXF -vf fps=1 output_%04d.png  

  In some videos, this yields images that, when the camera was moving, look much blurrier than when watching the video (see example below). The still frames from when the camera was not moving look sharper (closer to how it looks in video playback).

  The video specs are : mpeg2video, yuv422p, 1280x720 (according to FFprobe).

  Is this inherent within the video coding or structure ? The video looks so nice when in motion, but even when I pause in VLC the frame goes from sharp to blurred.

  Are there any additions to my FFmpeg code that could result in sharper images ? I tried adding a yadif filter, but it made no difference (the video isn’t interlaced anyways).

  Unfortunately I can’t post a video sample online, but below is an example of a sharper image and a blurry image ; both look in focus during video playback and are about a second apart in the video (that’s the same orange sea star on the left side).