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• avcodec/rl2 : Remove wrong check

  28 septembre 2022, par Andreas Rheinhardt

  avcodec/rl2 : Remove wrong check
  This check is intended to be avoid buffer overflows,
  
  yet there are four problems with it :
  
  1. It has an in-built off-by-one error : len == out_end - out
  
  is perfectly fine and nothing to worry about.
  
  This off-by-one error led to the pixel in the lower-right corner
  
  not being set properly for the back frame of the sample from
  
  the rl2 FATE-test. This pixel is copied to every frame which
  
  is the reason for the update to the reference file of said test.
  
  With this patch, the output of the decoder matches the output
  
  as captured from the reference decoder* (apart from the fact
  
  that said reference somehow lacks the top part of the frame
  
  (copied over from the background frame)).
  
  2. Given that the stride of the buffer may be different
  
  from the width of the video (despite one pixel taking one byte),
  
  there is a second check lateron making the first check redundant
  
  (if one returns immediately ; a simple break at the second check
  
  is not sufficient, because it only exits the inner loop).
  
  3. The check is based around the assumption of the stride being
  
  positive (it has this in common with the other check which
  
  will be fixed in a future commit).
  
  4. Even after fixing the off-by-one error, the check in
  
  question is still triggered by all the non-background frames
  
  in the FATE sample as well as by A1100100.RL2. In all these
  
  cases, they use len == 255 and val == 128. For videos with
  
  background frame this just means "copy from the background
  
  frame", which would be done anyway lateron.* Yet for videos
  
  without it copying it is necessary to avoid leaving
  
  uninitialized parts in the video.
  * : Available in https://samples.mplayerhq.hu/game-formats/voyeur-rl2/
  
  ** : Due to this, the code that copies the rest from the
  
  back frame is no longer executed for any of the samples
  
  available on the sample server. Given that these are only
  
  the files from the demo version of this game, I don't know
  
  whether this code is executed for any file in existence or not.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/rl2.c
  • [DH] tests/ref/fate/rl2

• How to Drop Duplicated frames that do not appear sequentially ?

  2 octobre 2022, par zgno

  As you might know, mpdecimate only drop frames that is similar to the PREVIOUS frame which means it only deals with sequentially duplicated frames. My problem is that just one same frame is duplicated throughout the whole video, and it is duplicated between frames(in other words, not sequentially,so mpdecimate always treats them as not duplicated) . It's almost like that frame is inserted randomly for a 1000+ times throughout the video. And I use ffmpeg -err_detect ignore_err -i only to find that no errors are detected. This strange situation happens in some hls streaming video. I will provide a small segment of the whole video for anyone who are interested to test.
A 6 seconds video down below, it is a badminton game.
A segment from the m3u8 file list

  


• How to Drop all matched frames that are the same with a specified frame

  2 octobre 2022, par zgno

  After researching into this for a couple of days, I found that mpdecimate only drop frames that is similar to the PREVIOUS frame. My problem is that just one same frame is duplicated throughout the whole video, and it is duplicated between frames(in other words, not sequentially,so mpdecimate always treats them as not duplicated) . It's almost like that frame is inserted randomly for a 1000+ times throughout the video. And I use ffmpeg -err_detect ignore_err -i only to find that no errors are detected. This strange situation happens in some hls streaming video. I will provide a small segment of the whole video for anyone who are interested to test.
A 6 seconds video down below, it is a badminton game.
A segment from the m3u8 file list