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• 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.

• How can I use ffmpeg to stream over http [closed]

  16 juillet 2024, par user3754828

  I am using the follow commands to stream to my localhost

  



  ffmpeg -i b.mp4 -r 60 -bufsize 1024k -vcode libtheora -qscale:v 1 -f ogg "udp://@127.0.0.1/video.ogg"

ffmpeg -i b.mp4 -r 60 -bufsize 1024k -vcode libtheora -qscale:v 1 -f ogg "http://127.0.0.1/video.ogg"


  



  The both work very well, at least do not show any errors, but when I try play such http stream does not, it gave me error "not found"

  



  Can somebody help me on it ? I am complety lost in this issue...also when I try include some port, for example ffmpeg -i b.mp4 -r 60 -bufsize 1024k -vcode libtheora -qscale:v 1 -f ogg "http://127.0.0.1:8980/video.ogg" provide me input/output error...I have test the equivalent commands on vlc and is work as well.

  



  Thanks in advance

  


• avcodec/adxdec : Remove unnecessary left-shift

  20 janvier 2020, par Andreas Rheinhardt

  avcodec/adxdec : Remove unnecessary left-shift
  Replace "(a * (1 << shift) * b + c) >> shift" by "a * b + (c >> shift)".
  
  It is equivalent to the old code because a is in the range of uint16_t,
  
  shift is 12 and b is effectively a signed 4-bit number, so that no
  
  overflow/truncation of high bits happens during the multiplication
  
  (overflow would be undefined anyway).
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/adxdec.c