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• can ffmpeg detect monochromatic parts of a video and conditionally set filter parameters accordingly

  15 juillet 2021, par Silentfury

  I have input videos that switch back and forth between coloured and monochrome/grey parts (frames that only contain luma information). Is there a way in ffmpeg to detect whether the current frame is coloured or monochrome and is it possible to use this information to change the parameters of a filter ?

  


  As an example I want to apply the mpdecimate filter and I want it to use a "hi" parameter of 50 (per pixel) for coloured frames and 20 for monochrome frames.

  


  So in pseudo code I want something something like

  


  -vf mpdecimate=hi=if(coloured,64*50,64*20)

  


  but obviously the "coloured" condition doesnt work that way.

  


  Is that somehow achievable ?

  


  PS :
Concernig the detection of monochrome frames I have identified two filters that have a related functionality but I am unable to use the information in another filter :

  


  

  • "geq" can get a good idea of frame colors using cbsum(x,y) and/or crsum(x,y)

  


  • "signalstats" can use the property "SATMAX" to tell about the color level of a frame

  


  


  Is there any way to use the resulting number of any of the two above filters in another filter ?

  


• Drop some parts of video and re-make key frames (c++ + libav)

  8 juillet 2021, par Hamed Masafi

  I'm trying to drop some parts of video in my app using libav, for example in a video that has 00:08:00 length, I try to drop frames 100-250 and 400-500 (Just for example).
I wrote this code that copy AVPacket and drop some packets, But there is a problem ! In our videos every keyframe followed by 29 non-key frames. So when my code goes to drop frames 100-250 the frame 100 may be is a non-key frame, in this case the parts that are going to join (In this example frame 250 to frame 400) the frame 400 is positioned after a keyframe that is not belogs to.

  


  In this section video frames shown garbled,

  


  Video cutting speed is so important in my code, so I can't decode/re-encode all of video frames.

  


  The question is that, How can I decode encode begin of each parts (from begin frame to first key frame) and make another frames copy without decode ?

  


  Or, Is there any another FAST solution for splitting/merging (Dropping some parts of video) ?

  


• Quickly split videos into parts with ffmpeg

  20 avril 2021, par RewossKy

  I'm doing splitting on FFMPEG. I divide 1.5 hour videos into 30 minutes. I have two ways of partitioning, the first is the method of rendering by recodecing on the top, I do not have any problem in this, but the time is quite long despite the GTX 1660s graphics card and the ryzen5 3500x processor.

  


  At the bottom, the time is short, but the first 3-4 seconds of the second part videos are frozen. Sometimes this causes problems like not reading in video editing programs.

  


  With recodec (slow, no problem)
ffmpeg -i 1.mp4 -vcodec libx264 -crf 30 -ss 00:00:00 -t 00:29:30 s1.mp4
ffmpeg -i 1.mp4 -vcodec libx264 -crf 30 -ss 00:29:31 -t 00:29:30 s2.mp4
ffmpeg -i 1.mp4 -vcodec libx264 -crf 30 -ss 00:59:01 -t 00:29:30 s3.mp4
ffmpeg -i 1.mp4 -vcodec libx264 -crf 30 -ss 01:28:30 -t 00:29:30 s4.mp4

  


  Without recodec (fast but have problem sometimes)
ffmpeg -i 1.mp4 -vcodec copy -ss 00:00:00 -t 00:29:30 s1.mp4
ffmpeg -i 1.mp4 -vcodec copy -ss 00:29:31 -t 00:29:30 s2.mp4
ffmpeg -i 1.mp4 -vcodec copy -ss 00:59:01 -t 00:29:30 s3.mp4
ffmpeg -i 1.mp4 -vcodec copy -ss 01:28:30 -t 00:29:30 s4.mp4