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• Revision 8830772370 : Multi-arf : Add code to turn it on and off. Add test code to turn multi-arf on a

  30 juin 2014, par Paul Wilkins

  Changed Paths :
   Modify /vp9/encoder/vp9_encoder.c

  
   Modify /vp9/encoder/vp9_encoder.h

  
   Modify /vp9/encoder/vp9_firstpass.c

  
  
  Multi-arf : Add code to turn it on and off.

  Add test code to turn multi-arf on and off depending
  on group length and zero motion.

  Changes to active max group length for mult-arf.

  Fund second arf only from normal frame bits.

  Change-Id : I920287fac1c886428c15a39f731a25d07c2b796c

• Clip long video segment quickly

  30 janvier 2020, par PRMan

  Let’s say I have a video called Concert.mp4. I want to extract a performance from it quickly with minimal reencoding. I want to do the equivalent of this, but faster :

  ffmpeg -i "Concert.mp4" -ss 00:11:45 -to 00:18:15  -preset veryfast -y artist.mp4

  This takes 17 seconds, which is way too long for our needs.

  Now, it turns out that 11:45 and 18:15 don’t fall on iframes, so if you try this you will get a 3 second delay at the beginning before the video shows :

  ffmpeg -i "Concert.mp4" -ss 00:11:45 -to 00:18:15 -c copy -y artist.mp4

  Running this command, we can see where we need to cut :

  ffprobe -read_intervals "11:00%19:00" -v error -skip_frame nokey -show_entries frame=pkt_pts_time -select_streams v -of csv=p=0 "Concert.mp4" > frames.txt

  So what we need to do is encode the first 3.708 seconds, copy the middle, and then encode the last 5.912 seconds.

  I can get the 3 segments to all look perfect (by themselves) like this :

  ffmpeg -ss 698.698 -i "Concert.mp4" -ss 6.302 -t 3.708 -c:v libx264 -c:a copy -c:s copy -y clipbegin.mp4
  
  
  
  ffmpeg -ss 708.708 -to 1089.088 -i "Concert.mp4" -c copy -y clipmiddle.mp4
  
  
  
  ffmpeg -ss 1089.088 -i "Concert.mp4" -t 5.912 -c:v libx264 -c:a copy -c:s copy -y clipend.mp4
  
  
  
  ffmpeg -f concat -i segments.txt -c copy -y artist.mp4

  segments.txt of course contains the following :

  file 'clipbegin.mkv'
  
  file 'clipmiddle.mkv'
  
  file 'clipend.mkv'

  I saw this solution presented here, but no amount of tweaking gets it to work for me :

  https://superuser.com/a/1039134/73272

  As far as I can tell, this method doesn’t work at all. It crashes VLC pretty hard no matter what I try.

  The combined video keeps glitching after the 3 seconds, probably because the PTS times are different or something (using some options, I have seen warning messages to this effect). Is there anything I can add to the commands above to get this to work ? The only requirement is that the middle command must not re-encode the video, but must do a fast copy.

  Thanks in advance.

• mute audio if the volume *exceeds* a threshold

  15 février 2023, par a1s2d3f4

  So, I have spent quite a bit of time looking for the answer but I get the exact opposite (something I already know how to do), namely, the audio below a certain threshold can get muted (can be done either with ffmpeg or sox).

  


  What I need is for the command to search my audio for anything that exceeds -18dB and mute all such segments. (The reason for this is because I have a recording where I am playing an electric piano with the audio output being recorded directly through the cable, but I am also recording from two microphones what I am speaking - between my playing. When I am playing the keyboard, the mics pick up a lot of action noise which I want to mute, and that's easy to do because the channel that records my piano input has piano sounds at that point and that corresponds exactly with when I want the audio from my mics to be muted, or at least attenuated.)

  


  Does anyone know if such a feat is possible ?
If it cannot be done with just one command, that's fine I'll try anything.