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• lavu/random_seed : use arc4random() when available

  7 décembre 2015, par Ganesh Ajjanagadde

  lavu/random_seed : use arc4random() when available
  arc4random() was designed as a superior interface for system random
  
  number generation, designed for OpenBSD and subsequently incorporated by
  
  other BSD’s, Mac OS X, and some non-standard libc’s. It is thus an improvement to
  
  use it whenever available.
  As a side note, this may or may not get included in glibc, and there is
  
  a proposal to create a posix_random family based on these ideas :
  
  http://austingroupbugs.net/view.php?id=859.
  Tested on Mac OS X.
  Signed-off-by : Ganesh Ajjanagadde <gajjanagadde@gmail.com>
  

  • [DH] configure
  • [DH] libavutil/random_seed.c

• vframes option ignored in ffmpeg ?

  25 mars 2016, par cooper

  I have a directory that contains 2001 PNG files. I can convert all of the frames to an mp4 video using ffmpeg and the following command :

  ffmpeg -framerate 60 -start_number 0 \
  
  -i pic.comp2.%07d.png -c:v libx264 -r 30 \
  
  -pix_fmt yuv420p input1ia.mp4

  This works fine. However, I am creating a more complicated application that needs to read only the first 1020 files in the directory (specifically 0 thru 1019). Some googling around led me to the -vframes option. My problem is — it seems to get ignored or at least interpreted differently than I expect.

  My modified command looks like :

  ffmpeg -framerate 60 -start_number 0 \
  
  -i pic.comp2.%07d.png -vframes 1020 -c:v libx264 
  
  -r 30 -pix_fmt yuv420p input1.mp4

  It seems like many other people doing the same thing as me do not encounter this issue. So I did some more digging. I tried changing vframes from 1020 to -vframes 20, and this seemed to work properly. So now I am thinking it might be some kind of mismatch between -framerate and -r ?

  The full resultant video is 33 sec long... which makes sense mathematically.

   1 sec
  
   ---------   x  2001 frames = 33.35 seconds
  
   60 frames

  That’s why I thought that specifying 1/2 of the PNGs as the ’end point’ would result in a video of the first 16-17 seconds. But I always get the full length video from using the -vframes option.

  I assume my input to -vframes must be incorrect mathematically, since a small number of frames seems to work. However, I do not understand why.

  The most educated guess I can seem to make is that it is reading the PNGs as 60fps (-framerate), but the -r makes the output video 30fps or something ? However, then I would assume that the full output video would not be 33 seconds long.

• vframes option ignored in ffmpeg ?

  25 mars 2016, par cooper

  I have a directory that contains 2001 PNG files. I can convert all of the frames to an mp4 video using ffmpeg and the following command :

  ffmpeg -framerate 60 -start_number 0 \
  
  -i pic.comp2.%07d.png -c:v libx264 -r 30 \
  
  -pix_fmt yuv420p input1ia.mp4

  This works fine. However, I am creating a more complicated application that needs to read only the first 1020 files in the directory (specifically 0 thru 1019). Some googling around led me to the -vframes option. My problem is — it seems to get ignored or at least interpreted differently than I expect.

  My modified command looks like :

  ffmpeg -framerate 60 -start_number 0 \
  
  -i pic.comp2.%07d.png -vframes 1020 -c:v libx264 
  
  -r 30 -pix_fmt yuv420p input1.mp4

  It seems like many other people doing the same thing as me do not encounter this issue. So I did some more digging. I tried changing vframes from 1020 to -vframes 20, and this seemed to work properly. So now I am thinking it might be some kind of mismatch between -framerate and -r ?

  The full resultant video is 33 sec long... which makes sense mathematically.

   1 sec
  
   ---------   x  2001 frames = 33.35 seconds
  
   60 frames

  That’s why I thought that specifying 1/2 of the PNGs as the ’end point’ would result in a video of the first 16-17 seconds. But I always get the full length video from using the -vframes option.

  I assume my input to -vframes must be incorrect mathematically, since a small number of frames seems to work. However, I do not understand why.

  The most educated guess I can seem to make is that it is reading the PNGs as 60fps (-framerate), but the -r makes the output video 30fps or something ? However, then I would assume that the full output video would not be 33 seconds long.