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• avcodec/hevc_ps : fix the problem of memcmp losing effectiveness

  29 mars 2024, par Tong Wu

  avcodec/hevc_ps : fix the problem of memcmp losing effectiveness
  HEVCHdrParams* receives a pointer which points to a dynamically
  
  allocated memory block. It causes the memcmp always returning 1.
  
  Add a function to do the comparision. A condition is also added to
  
  avoid malloc(0).
  Reviewed-by : James Almer <jamrial@gmail.com>
  
  Signed-off-by : Tong Wu <tong1.wu@intel.com>
  
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavcodec/hevc_ps.c
  • [DH] libavcodec/hevc_ps.h

• FFmpeg problem while writing streams to file

  23 septembre 2011, par NoviceAndNovice

  I finally "able" to write video stream packets to a file using the function

  av_interleaved_write_frame(outputContext, &packet);

  But after a short period of time i got this error :

  Application provided invalid, non monotonically increasing dts to muxer 
  
  in stream 0: *numberX* >= *numberY*

  Anybody has any idea, what may cause this ? And how to fix it ?

  Best Wishes

• Extract frames from a video results in abnormaly more frames for each fps by using ffmpeg

  15 juin 2021, par alanzzz

  I have a job of using ffmpeg to extract the frames averagely from a video, with different fps. I use this command for it.

  


  ffmpeg -i input.mp4 -r specified_fps -q:v 2 image %4d.png

  


  And I have 3 questions about this task.

  


  

  1. What I expect is that if I double the fps, the number of extracted frames will also get doubled. However, that's not the case. Take one of the input videos as an example. I get 2 extra frames for all the sample factors (80 / 158 / 236 / 392 v.s. 78 / 156 / 234 / 390). Does it related to the mechanism of picking/dropping frames when extracting frames from a video？ (credit to @Tom Yan)

  


  


  video info

  


  

  • Duration : 1min18s

  


  • Frame rate mode : constant (CFR)

  


  • Frame rate : 30.0 FPS

  


  • Total number of frames : 2340

  


  


  Config setting & results

  


  





  


  


  


  


  


  



  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  FPS	Actual num of frames	correct num of frames
  1	80	78
  2	158	156
  3	236	234
  5	392	390

  


  


  


  2. I check for the output images, the extracted frames for different fps are totally different from each other. In other words, for example, the 1st image for fps=1 is not the same as the 1st image for fps=2. Is that legitimate ? And is it possible for me the get some identical images for different fps ?

     


  


  3. The last problem is that for some videos I use, the difference between the 1st and 2nd image is different from the difference between the 2nd and 3rd. While for the remaining images, the differences become average. To be specific, there is only a slight change from 1st to 2nd frame, while for 2nd to 3rd, 3rd to 4th, and so on, the changes are the same, which is normally distributed according to the specified FPS. I am wondering why such a case happens ? Does it relate to the I-frame, B-frame, P-frame, GOP, or IDR ?

     


  


  


  I am new to this field and cannot find some useful info from other places. I've tried my best to describe my questions clearly. Feel free to leave some comments. Any help would do me a great favor. Thanks in advance !