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• Why is the resulting clip of my ffmpeg concatenation much longer than expected ?

  21 mai 2018, par joeycato

  I’d like to extract a set of clips from a 60fps input video, change each of their durations, then recombine those modified clips. Unfortunately when I attempt this, the resulting clip doesn’t exactly match the sum of those durations.

  Here’s my repro case :

  1. Extend an extracted 2-second clip to 4 seconds ( input frame count = 120 = 60fps * 2 sec ) )

  ffmpeg -y -ss 8 -t 2 -i ./clip_60fps.avi -filter:v "settb=(4/120),setpts=(4/120)*N/TB" -r 120/4 -vcodec huffyuv step1.avi

  2. Shorten an extracted 4-second clip to 1 second ( input frame count = 240 = 60fps * 4 sec )

  ffmpeg -y -ss 10 -t 4 -i ./clip_60fps.avi -filter:v "settb=(1/240),setpts=(1/240)*N/TB" -r 240/1 -vcodec huffyuv step2.avi

  3. Concatenate the modified clips :

  mylist.txt contents :

  file './step1.avi'
  
  file './step2.avi'

  ffmpeg -y -safe 0 -f concat -i ./mylist.txt -r 60 -vcodec huffyuv steps_joined.avi

  The result :

  ffmpeg -i step1.avi 2>&1 | grep Duration
  
  ffmpeg -i step2.avi 2>&1 | grep Duration
  
  ffmpeg -i steps_joined.avi 2>&1 | grep Duration

  Duration : 00:00:04.00, start : 0.000000, bitrate : 3228 kb/s

  Duration : 00:00:01.00, start : 0.000000, bitrate : 23132 kb/s

  Duration : 00:00 :39.98, start : 0.000000, bitrate : 910 kb/s

  Why am I not getting an exact result of 5 seconds, but instead a much larger value ?

• Constant Frame Rate Video extracting more frames than expected - FFMPEG

  22 septembre 2023, par superand12

  I'm trying to extract 1 frame per second in a 3 second video that has a video frame rate of 30 fps.

  


  ffmpeg -i 3seconds.mp4 -r 1 -q:v 2 output_%04d.jpg

  


  I noticed that this command was returning 5 frames instead of 3. I then run this command to figure out that there are iframes in the video (not sure if thats the reason).

  


  ffprobe -v error -select_streams v:0 -show_frames -show_entries frame=pict_type -of csv 3seconds.mp4

  


  This may have been redundant but adding this filter flag gave me exactly 3 frames. Unclear about the underlying frame selection process.

  


  ffmpeg -i 3seconds.mp4 -filter:v fps=1 -r 1 -q:v 2 output_%04d.jpg

  


  Video info :

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '3seconds.mp4': Metadata: major_brand     : isom minor_version   : 512 compatible_brands: isomiso2avc1mp41 encoder         : Lavf58.20.100 Duration: 00:00:03.07, start: 0.000000, bitrate: 2753 kb/s Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc), 1920x1080 [SAR 1:1 DAR 16:9], 2747 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default) Metadata: handler_name    : GoPro AVC vendor_id       : [0][0][0][0] timecode        : 19:56:41:04 Stream #0:1(eng): Data: none (tmcd / 0x64636D74), 0 kb/s Metadata: handler_name    : GoPro AVC timecode        : 19:56:41:04

  


• FFmpeg : Frame sizes of the generated video are extremely larger than the expected [closed]

  8 février 2021, par bbasaran

  I am recording frames (screen buffer) as NumPy arrays during the game which runs on the resolution of "400x225". Each frame array is a size of 270.1 kB.

  


  After saving those frames, I create an mp4 file with the following bash command (The game runs in 35 FPS (frames/second)) :

  


  ffmpeg -r 35 -f image2 -i frame%05d.png -vcodec libx264 -crf 1 video.mp4


  


  Then I have used a tool to generate a CSV file of frame data from the video created with the command above. The output is here below. The weird this is that, if we sum those first 35 frames (video was recorded with "-r 35" parameter because game runs in 35 FPS), we get approximately 18k kbit.

  


  18k kbit/sec bitrate is super high for a 400x225 video. What am I doing wrong while generating the video ? I appreciate any help, thanks !