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• 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

  


• How to segment audio and video to the same segments number ?

  24 décembre 2019, par julian zapata

  I’ve extracted audio and video from the same mp4 file and created different variants for different resolutions. When I segment the videos and the audio file with MP4Box, the video segments are the same segments number but the audio segments have one more. I need the video and audio segments to be the same number to use with dash.

  I’m using the next commands to produce the video and audio files :

  Command to extract the audio from mp4 file :

  ffmpeg -y -i "transformers.mp4" -c:a aac -b:a 192k -vn "transformers_audio.m4a"

  Produce each variant of the video with the next command modifying the resolution and bitrate parameters :

  ffmpeg -i transformers.mp4 -c:v libx264 -r 24 -x264opts "keyint=48:min-keyint=48:no-scenecut" -an -vf scale=640:360 -b:v 750k -dash 1 transformers_640x360_750k.mp4

  Generate the mpd file and segment the videos and audio each 4 seconds with :

  mp4box -dash 4000 -profile "dashavc264:live" -bs-switching no -sample-groups-traf \ 
  
  -out output4\ 
  
  transformers.mpd \ 
  
  transformers_480x270_400k.mp4 \ 
  
  transformers_640x360_800k.mp4 \ 
  
  transformers_960x540_1200k.mp4 \
  
  transformers_1280x720_1500k.mp4 \ 
  
  transformers_1920x1080_4000k.mp4 \
  
  transformers_audio.m4a

  This produces 36 segments for each variant of the video and 37 for the audio. How to solve this little variation ? How to make the audio segments number exactly the number of video segments ?

• avcodec/cfhdenc : use pts instead of frame number

  19 février 2021, par Paul B Mahol

  avcodec/cfhdenc : use pts instead of frame number
  Makes encodes bitexact with different number of threads.
  

  • [DH] libavcodec/cfhdenc.c