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• ffmpeg FPS information mismatch with the video

  8 décembre 2017, par Adorn

  I have a bunch of videos with some statistics of what is happening inside a video. One such piece of information is given in terms of time of the video in seconds up to one decimal point.

  To get the FPS of a video, I am using ffmpeg -i

  But when I manually compute one particular frame’s time using given FPS, it does not match.

  For example, ffmpeg outputs FPS = 30.

  I look at the video statistics, the frame at the 156.8 = 2.368 has to be
  4704'th frame. I open the video using ’skvideo’, read all the frames, and view the 4704'th frame. It is some frame around time 2.12 ?. I checked multiple such instances in multiple videos and this is a common behavior.

  I do not understand why this is so and how can I get around the problem ?

  As such I am not bounded by ffmpeg. Skvideo is being used to read the videos. I tried opencv, as of now it does not work with VideoCapture, and reinstalling it is costly for me time wise. But I guess ’opencv/skvideo’ should not matter, one can count the frames manually as well.

  So, in the solution, I am looking out for -

  1. Given timestamps of inside of a video, how can I find a frame of that particular time location ?

  2. In case someone might have already worked on this, this is related to THUMOS dataset. I am on Ubuntu 16.04

  EDIT_1

  Actually I can be more specific as it is a publicly available data. The time bounds are of an important activity. For example, in a video, when does basketball dunk occurs ? It is given in pairs - [start end]. Some videos have multiple activities, some have only one.

  Here is a sample video, and following are the activity times.

  [[  16.5, 20.8],
  
  [  26.6, 32.2],
  
  [  34.8, 42.1],
  
  [  47.8, 50.0],
  
  [  58.1, 62.9],
  
  [  65.6, 67.2],
  
  [  68.5, 74.0],
  
  [  76.4, 78.3],
  
  [  78.7, 79.8],
  
  [  80.8, 82.1],
  
  [  85.0, 87.3],
  
  [  90.1, 91.4],
  
  [  98.5, 100.3]]

  I also tried checking manually, 32.87 FPS "almost" works for few videos but not for all. and almost means it is off by 10 frames. This is a huge difference for my task, and I need exact frame.

  Also, there has to be some way, because it can be visually observed with multiple video players that times in the dataset are correct.

• ffmpeg : fix implementation of updated input start time

  21 octobre 2022, par Gyan Doshi

  ffmpeg : fix implementation of updated input start time
  The current adjustment of input start times just adjusts the tsoffset.
  
  And it does so, by resetting the tsoffset to nullify the new start time.
  
  This leads to breakage of -copyts, ignoring of input_ts_offset, breaking
  
  of -isync as well as breaking wrap correction.
  Fixed by taking cognizance of these parameters, and by correcting start times
  
  just before sync offsets are applied.
  

  • [DH] fftools/ffmpeg.c
  • [DH] fftools/ffmpeg.h
  • [DH] fftools/ffmpeg_demux.c
  • [DH] fftools/ffmpeg_opt.c

• Revision 5a5df19de3 : New default coefficient/band probabilities. Gives 0.5-0.6% improvement on derf

  12 décembre 2012, par Ronald S. Bultje

  Changed Paths : Modify /vp9/common/vp9_default_coef_probs.h Modify /vp9/encoder/vp9_tokenize.c New default coefficient/band probabilities. Gives 0.5-0.6% improvement on derf and stdhd, and 1.1% on hd. The old tables basically derive from times that we had only 4x4 or only 4x4 and 8x8 DCTs. Note (...)