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• Revision 82757250d6 : Merge "Refactor to remove speed feature dependency on mode search order"

  11 septembre 2014, par Jingning Han

  Changed Paths :
   Modify /vp9/encoder/vp9_speed_features.c

  
  
  Merge "Refactor to remove speed feature dependency on mode search order"

• Identify a specific frame number of a video file

  23 février 2017, par James Crampton

  I have a video file from which I’ve extracted a specific frame to analyze. However, I want to know what the frame number of this frame is.
  I can’t seem to find anything. I’ve had a look at ffmpeg showinfo, but that doesn’t seem to work.
  I’ve also looked into exifread, which produced information about the frame - except for the frame number.

  Any ideas ?

• How to insert frames to compensate for frames lost during capture

  5 novembre 2015, par JMor

  My original clip was 22:47 long. I captured the video in avi with Ut Video Lossless Codec at 29.97 fps, with pcm 16 bit unsigned audio.
  I am using Virtualdub with VHScrCap driver for capture.
  Virtualdub and mpc and potplayer play the captured file apparently too fast, but with the right audio pitch in the first 3-4 min, but high pitch in the rest of the video. The duration is 19:06, shorter than the original 22:47 (confirmed by mediainfo)
  The cause of the problem seems to be that I am losing more frames when capturing large HD frames.

  Regular encoding

  Encoding captured clip to mp4 :

  ffmpeg -ss 3.25 -i input.avi -map 0:0 -map 0:1 -threads 0 -c:v libx264 -profile:v main \
  
  -preset:v medium -level 3.1 -x264opts crf=26.0 -aspect 16:9 -t 1112.69 \
  
  -y -f mp4 -vf "crop=1432:808:4:46, hqdn3d=1.5:1.5:6:6, \
  
  scale=1216:684, pad=1280:720:32:18" -c:a ac3 -ac 2 -ar 48000 -b:a 160k \
  
  output.mp4

  The output is 18:32 long, framerate is still 29:97. The audio pitch is OK in the first 2 minutes, and way too high in the rest of the video.

  Trying to correct

  I try to correct it in three steps by (1) encoding a video stream that is slowed down to 23.976 fps and extracting a wav audio stream, (2) slowing speed and pitch of audio and (3) remuxing video and audio :
  (1)

  ffmpeg -ss 3.25 -i input.avi -threads 0 \
  
  -c:v libx264 -profile:v main -preset:v medium -level 3.1 -x264opts crf=26.0 \
  
  -aspect 16:9 -t 1390.862 -an -y -f mp4 -r 24000/1001 \
  
  -vf "crop=1432:808:4:46, hqdn3d=1.5:1.5:6:6, scale=1216:684, pad=1280:720:32:18, \
  
  setpts=1.25*PTS" video_out.mp4  \
  
  -t 1112.69 -y -vn -f wav  audio_out.wav

  (2) The wav audio stream is then slowed down with lower pitch with sox :

  sox --norm audio_out.mp4.wav audio_out-24.wav speed 0.8

  (3) The two streams are then remuxed with :

  ffmpeg -i video_out.mp4 -i audio_out-24.wav -map 0:0 -map 1:0 -c:v copy \
  
  -c:a ac3 -ac 2 -af aresample=resampler=soxr -ar 48000 -b:a 160k \
  
  final_output.mp4

  This time, the video duration (23:10) is closer to the original, the pitch is OK for the whole video except for the first 2-3 minutes, where it is (predictably) too low.

  I have a sense that (1) the capture log, and ffprobe give the frame by frame information that show what is the ’instantaneous’ real frame rate, and (2) that information is not used by ffmpeg encoding, but presumably could be used to correct the frame rate by inserting duplicate or interpolated frames to restitute the correct frame rate. I suspect I could get the information from (1), but have no clue how to do (2).

  If someone familiar with this type of issue could give me some advice, and point me in the right direction, I would really appreciate.