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• ffprobe reading wrong frame rate, any workarounds besides MediaInfo ?

  20 mai 2023, par Minty

  I want to check the frame rate of many videos. I decided to employ ffprobe :

  


  ffprobe -v error -select_streams v -of default=noprint_wrappers=1:nokey=1 -show_entries stream=r_frame_rate faulty.mkv =

  


  500/21


  


  That can't be right, what kind of fps is 500/21 ?

  


  ffprobe faulty.mkv (version 4.3.5-0+deb11u1+rpt3)

  


  Stream #0:0: Video: (...), 23.81 fps, 23.81 tbr, 1k tbn, 23.98 tbc (default)


  


  At least ffprobe 4 read the correct codec timescale i.e. 23.98 tbc (default), but in later versions tbc has been deprecated :

  


  Stream #0:0: Video: (...), 23.81 fps, 23.81 tbr, 1k tbn (default)


  


  However, MediaInfo gets it right :

  


  mediainfo faulty.mkv =

  


  (...)
Frame rate mode                          : Constant
Frame rate                               : 23.976 (24000/1001) FPS
(...)


  


  I tried using -count_packets to then divide nb_read_packets of the stream by the duration of the file, I'm getting 1 second per hour error. This is much better compared to 23,8095, but packets are not frames, and only the prohibitively, unusably slow -count_frames gets me the exact value.

  


  The rest of my workflow uses ffprobe, so I'm reluctant to switch to MediaInfo completely. I get that the file is, well, faulty, but if mediainfo can do it, is there a way to make sure the correct frame rate is read with ffprobe without decoding the entire file as -count_frames seems to do ?

  


• Why is ffmpeg cut setting the wrong duration on my output file

  9 mai 2023, par danielson317

  Setup

  


  I am trying to break a video up into parts using some basic commands I have seen available.

  


  I have tried :

  


  ffmpeg -ss 00:00:00 -t 00:11:42 -i 'original.m4v' -acodec copy -vcodec copy 'output.m4v'

  


  I also tried more generic (and much slower) :

  


  ffmpeg -ss 00:00:00 -t 00:11:42 -i 'original.m4v' 'output.m4v'

  


  I am on Ubuntu 20 with ffmpeg 4.2.7-0. I know it is a little outdated but this computer lost it's network card so I cannot update it at this time.

  


  The problem

  


  In both cases the video cuts correctly to only have the first 11:42. However the video properties state the video is 31 minutes long (the length of the original). This file size also reflects the reduced size I would expect from the cut. When I play the video in VLC it reports the video is 31 minutes long but scanning or playing past 11:42 "crashes" the playback.

  


  Question

  


  Why is the new video reporting the wrong length and how do I correct this ? Preferably in the conversion process not a secondary command.

  


• ImageJ / Fiji shows wrong number of frames in video (FFMPEG import)

  28 avril 2023, par locoric_polska

  I am counting the number of animals in a an area using Fiji. I import the video through the FFMPEG plug-in (videos are mp4 with mpeg-4 codec). However, I noticed that when I import the videos Fiji uploads the wrong number of frames, and I cannot understand why and how.

  


  An example. I have a video shot at 25fps which is 1582s long. If I do the calculations the video should have 39550 frames in total (1582*25). When I open it through a Computer vision package in R, I see that the video correctly contains 39550 frames. However, when loaded in Fiji, the shown number of frames is 49511. So Fiji is adding 9961 frames to the video. This is consistent across all videos that are recorded in 25fps, while it does not appear in videos shot at 24fps.

  


  Curiously, I found that the ratio between the number of frames read by Fiji and the 'real' number of frames is consistent between 0.79 and 0.80. This makes me think that Fiji is expecting the video to be 30fps and (possibly) duplicating frames to adjust the video to this assumption.

  


  Unfortunately, I discovered all this after finishing my analysis and while trying to merge this dataset with another obtained through CV. The number of frame does not match between datasets and I am not sure how to solve this.

  


  Any help would be greatly appreciated !!

  


  An idea is to multiply all the frame numbers by 0.8 to adjust them to the old assumption. This solution assumes that Fiji is duplicating frames throughout the video in a consistent way