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• How to concat videos and apply filters to one/both of them in one render ?

  29 juillet 2019, par NeeFuu

  I am merging two files but one of them needs hard subtitle applied. I can hardcode once and then concat files but because of codec conflict, it needs encoding two times which I want to avoid because of performance issues.

  I have tried to add simple subtitle in filter complex, which I found in this documentation. Then I tried to apply it on concat video filter example code found on StackOverflow.

  ffmpeg -i segment.mp4 -i video.mp4 -filter_complex "[0:v] [0:a] [1:v] ass=subtitle.ass [1:a] concat=n=2:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" output.mkv

  I have tried to add subtitle only for video.mp4 but then I got :

  [Parsed_ass_0 @ 000002db090dd000] Shaper: FriBidi 1.0.4 (SIMPLE)
  
  [Parsed_ass_0 @ 000002db090dd000] Using font provider directwrite
  
  [Parsed_ass_0 @ 000002db090dd000] Added subtitle file: 'subtitle.ass' (2 styles, 3 events)
  
  [AVFilterGraph @ 000002db096e6680] Too many inputs specified for the "ass" filter.
  
  Error initializing complex filters.
  
  Invalid argument

  I am not sure If I am just adding filter wrong or it’s just wrong way to do it.

• Grid/Mesh warping of videos with OpenCV

  2 février 2017, par andreas

  I would like to do some warping with OpenCV applied on Videos. Here is a demo in Javascript which perfectly explains what I want to achieve via OpenCV :

  http://persistent.info/web-experiments/distortion/
  Please select "Tron Legacy" in the drop down menu "Datasource"

  Here is also screenshot of the demo :

  Screenshot of the Demo

  I am not an expert in OpenCV, but as far as I know there are only methods about camera calibration which deals with distortions (but only with special ones like radial and tangential distortions). For my purpose, I need a more general approach.

  The overall goal : apply some kind of "filter" on any video which generates this kind of distortion, based on a grid which can be adjusted via drag and drop by a user. This filter does not have to work in real time. Hence, if you know any other frameworks which can be used for this, please let me know :-) I´ve checked the filter section of FFMPEG, but it seems that also these filters are not appropriate.

  Thanks for your help !!

• How to manipulate YUV frames obtained from an ffmpeg video decoder ?

  23 juillet 2014, par user3665376

  I wanted to apply effects on video while rendering on android . I decoded the mpeg4 video using ffmpeg to raw YUV(YUV420P) frames .

  I modified the Y(luminescence) bytes using the below snippet and rendered it to screen after converting it to RGB frames .

  AVFrame *frame = [YUV420P frame recieved from ffmpeg decoder]
  
  uint8_t *tempPtr = NULL;
  
  tempPtr = frame->data[0];
  
  int j;
  
  for(j = 0 ; j < frame->linesize[0] ; j++){
  
      *(tempPtr++) = 1;
  
  }

  I applied a Y value of 1 to all pixels of all frames . I expected an output video of low luminescence ie.much darker video . But I was not able to notice any change in luma of the rendered video .

  Note : The YCbCr data planes at AVFRame.data[0] , AVFrame.data[1] , Avframe.data[2] of the decoded frame has expected values . The AVFrame.buf pointers were all pointing to NULL (Don’t know whether it has anything to do with data).

  Wanted to know whether anybody has encountered this situation before ??Links to related opics also will be very much helpful.

  Thanks.