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• Why are Cb and Cr planes displaced differently from lum by the displace complex filter in ffmpeg ?

  10 janvier 2024, par Neb

  I have a video encoded with the yuv420p pixel format and I want to displace its pixels. I'm using ffmpeg and its new displace filter. The filter takes as inputs (the video to be displaced and) two displacement maps respectively for X and Y axis. I decided to create the displacement maps directly into ffmpeg using the nullsrc video source filter and the geq filter to specify the value of the three planes : lum, Cb, Cr. The script is the following :

  



  ffmpeg INPUT.mp4 -f lavfi -i nullsrc=size=${WIDTH}x${HEIGHT}:d=0.1,geq='lum=128+30*sin(2*PI*X/400):Cb=128+30*sin(2*PI*X/400):Cr='128+30*sin(2*PI*X/400)' -f lavfi -i nullsrc=size=${WIDTH}x${HEIGHT}:d=0.1,geq='lum=128+30*sin(2*PI*X/400):Cb=128+30*sin(2*PI*X/400):Cr=128+30*sin(2*PI*X/400)' -lavfi '[0][1][2]displace' OUTPUT.mp4


  



  I used the example provided in the documentation of ffmpeg, since the expression used in geq is irrelevant for the purposes of the problem.

  



  At the and of the computation, I get the pixels of the input video not properly displaced, meaning that I can clearly see a sort of ghost carrying-color-information video under a displaced but b/w one.
After some tests, I noticed that the displacemnt map created had only the luma plane displaced correctly while the chrominance planes were displaced, but differently from luma, which is the origin of the planes disalignment in the intput video as you can see in the following extract frames :

  



  

  



  I also noticed that the video describing the Cb and Cr planes of the displacement maps have half resolution of the luma plane.

  



  My question is : how can i setup correctly the Cr and Cb planes in the geq definition so that they are exactly identical to the luma plane ?

  



  It would be also great if someone could explain me why ffmpeg gives me an output so much different for luma and Cb, Cr planes even if the function provided is the same.

  



  If, it can help, i'm using ffmpeg 3.3-static build.

  



  Thanks for your time.

  


• ffmpeg slower than downloading

  7 août 2017, par Krylic

  When trying to get a clip of a video from a remote source
  Input source :
  

  ffprobe version 3.3.2-static http://johnvansickle.com/ffmpeg/  Copyright (c) 2007-2017 the FFmpeg developers
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'http://website.com/video.mp4':
 Metadata:
   major_brand     : mp42
   minor_version   : 0
   compatible_brands: mp42mp41
   creation_time   : 2017-07-13T15:44:58.000000Z
 Duration: 00:57:32.42, start: 0.000000, bitrate: 1939 kb/s
   Stream #0:0(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv), 720x480 [SAR 10:11 DAR 15:11], 1745 kb/s, 29.97 fps, 29.97 tbr, 29970 tbn, 59.94 tbc (default)
   Metadata:
     creation_time   : 2017-07-13T15:44:58.000000Z
     handler_name    : Mainconcept MP4 Video Media Handler
     encoder         : AVC Coding
   Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 189 kb/s (default)
   Metadata:
     creation_time   : 2017-07-13T15:44:58.000000Z
     handler_name    : Mainconcept MP4 Sound Media Handler

  Current command :
  ffmpeg version 3.3.2-static
  ffmpeg.linux -threads 2 -y -ss 3273 -i "http://website.com/video.mp4" -an -movflags +faststart -preset veryfast -codec copy /outputfolder/trimmed_video.mp4
  This 5m35.102s to create a 45mb 2min file.

  If I download the file using wget it takes 28s and using ffmpeg only takes 0.243s

  If I add -vn OR -an to the output portion of the command it completes the trim in about 2.101s. Meaning it’s faster to download the two stream and merge them myself.

  Can anyone explain this behaviour and why my first command takes so long when on a lot of other video files it’s very fast ?

• ffmpeg http slower than downloading first

  9 août 2017, par Krylic

  When trying to get a clip of a video from a remote source
  Input source :
  

  ffprobe version 3.3.2-static http://johnvansickle.com/ffmpeg/  Copyright (c) 2007-2017 the FFmpeg developers
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'http://website.com/video.mp4':
 Metadata:
   major_brand     : mp42
   minor_version   : 0
   compatible_brands: mp42mp41
   creation_time   : 2017-07-13T15:44:58.000000Z
 Duration: 00:57:32.42, start: 0.000000, bitrate: 1939 kb/s
   Stream #0:0(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv), 720x480 [SAR 10:11 DAR 15:11], 1745 kb/s, 29.97 fps, 29.97 tbr, 29970 tbn, 59.94 tbc (default)
   Metadata:
     creation_time   : 2017-07-13T15:44:58.000000Z
     handler_name    : Mainconcept MP4 Video Media Handler
     encoder         : AVC Coding
   Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 189 kb/s (default)
   Metadata:
     creation_time   : 2017-07-13T15:44:58.000000Z
     handler_name    : Mainconcept MP4 Sound Media Handler

  Current command :
  ffmpeg version 3.3.2-static
  ffmpeg.linux -threads 2 -y -ss 3273 -i "http://website.com/video.mp4" -an -movflags +faststart -preset veryfast -codec copy /outputfolder/trimmed_video.mp4
  This 5m35.102s to create a 45mb 2min file.

  If I download the file using wget it takes 28s and using ffmpeg only takes 0.243s

  If I add -vn OR -an to the output portion of the command it completes the trim in about 2.101s. Meaning it’s faster to download the two stream and merge them myself.

  Can anyone explain this behaviour and why my first command takes so long when on a lot of other video files it’s very fast ?