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• How to capture screenshots from a video clip 50 minutes into the clip and do it fast ?

  3 janvier 2015, par Mint

  Ok it seems that whenever I tell ffmpeg to take a screen cap half way though the clip (clip can be as long as 10 hours) it uses 100% of 1 cpu core and takes ages… whereas if I let it do a frame at the start it goes real quick, as if it scans though the video to get to the middle instead of just jumping to it !

  Here is the code im currently using :

  ffmpeg -y -itsoffset -“500"  -i “clipname.mov" -vcodec png -vframes 1 -an -f rawvideo “clipScreenshot001.png”

  This can take several minutes.

  These are HD videos too, 720p/1080p and allot of the time they are raw unedited clips (e.g. very long).

  So I was hoping for some better software that will make screen captures from video much faster (has to be linux and scriptable).

• Revision 8f9d94ec17 : SSSE3 Optimization for Atom processors using new instruction selection and order

  5 décembre 2014, par levytamar82

  Changed Paths :
   Modify /vp9/common/x86/vp9_subpixel_8t_ssse3.asm

  
  
  SSSE3 Optimization for Atom processors using new instruction selection and
  ordering

  The function vp9_filter_block1d16_h8_ssse3 uses the PSHUFB instruction which has
  a 3 cycle latency and slows execution when done in blocks of 5 or more on Atom
  processors.
  By replacing the PSHUFB instructions with other more efficient single cycle
  instructions (PUNPCKLBW + PUNPCHBW + PALIGNR) performance can be improved.
  In the original code, the PSHUBF uses every byte and is consecutively copied.
  This is done more efficiently by PUNPCKLBW and PUNPCHBW, using PALIGNR to
  concatenate the intermediate result and then shift right the next consecutive 16
  bytes for the final result.

  For example :
  filter = 0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8
  Reg = 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
  REG1 = PUNPCKLBW Reg, Reg = 0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7
  REG2 = PUNPCHBW Reg, Reg = 8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15
  PALIGNR REG2, REG1, 1 = 0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8

  This optimization improved the function performance by 23% and produced a 3%
  user level gain on 1080p content on Atom processors.
  There was no observed performance impact on Core processors (expected).

  Change-Id : I3cec701158993d95ed23ff04516942b5a4a461c0

• ffmpeg : generate different multibitrate video from single input

  26 septembre 2016, par Stack Overflow

  I want to generate multiple multibitrate files from one single resource.

  I want to generate 4 different quality file : 240p , 360p , 720p , 1080p.

  My requirement is suppose i provide a file having 360p quality then only 2 file get generated
  1) 240p
  2) 360p

  If, I provide a file having 720p quality then 3 files get generated
  1) 240p
  2) 360p
  3) 720p

  Exactly same like youtube. (If you upload higher quality video then it provides more quality option , if you upload lower quality video then it provide less quality option).

  Is there any ffmpeg command which do same ? i.e from single input source it identify and generate multibitrate file of lower bitrate automatically.