Recherche avancée

Sur d’autres sites (8584)

• FFMPEG : Fixing stutter in low-motion areas

  11 juillet 2018, par stevendesu

  I’m trying to create videos with a very specific handful of requirements using FFMPEG :

  • Must have a very low (ideally less than 0.5 seconds) keyframe rate
  • Must have a moderately low ( 1Mbps) bitrate
  • Must run at a reasonable ( 24fps) framerate
  • Must have a width multiple of 4
  • Must not have any B-frames
  • Must be H.264 baseline encoded
  • Must be FLV

  Encoding speed is of no concern. If it takes 2 minutes to encode 1 second of video, that’s absolutely fine. What matters is that the output retains quality at the lowest possible bitrate.

  To this effect I currently have the following FFMPEG command :

  ffmpeg \
  
      -fflags +genpts \
  
      -i big_buck_bunny_1080p_stereo.avi \
  
      -vf "scale=trunc(360*iw/ih/4)*4:360" \
  
      -vf "settb=1/1000" \
  
      -r 24 \
  
      -g 6 \
  
      -keyint_min 6 \
  
      -force_key_frames "expr:gte(t,n_forced/4)"\
  
      -c:v libx264 \
  
          -preset veryslow \
  
          -tune zerolatency \
  
          -profile:v baseline \
  
          -pix_fmt yuv420p \
  
      -b:v 1000k \
  
      -c:a speex \
  
          -ar 16000 \
  
          -ac 1 \
  
      -b:a 64k \
  
      -f flv bbb_lo.flv

  I wish to experiment with various encoding options (me_method, subq, etc) to see how they all affect quality and bitrate. Before that, though, I’ve got an immediate quality issue to address with the command above.

  See the video here on YouTube

  I’ve clipped just a portion of the video that really demonstrates the issue. When an area of the screen undergoes very slight changes in color, there are no motion vectors. This means that certain sections of the video go un-updated until the next keyframe. This can be seen strongly in the tree on the left at the beginning of the video or in the bunny while he’s still asleep. If a viewer were staring at certain regions of the screen it may look like the video is only running at 4 frames per second (my keyframe rate) even though the video is actually running at 24 frames per second — it just isn’t updating the entire screen.

  I’d be okay if these areas of the screen became heavily blurred so long as the motion is preserved. Doing a bit of research I thought that the options -flags2 -fastpskip would fix this, however this option is not working for me :

  [libx264 @ 0x55b63e32c760] [Eval @ 0x7ffea2a7a830] Undefined constant or missing '(' in 'fastpskip'
  
  [libx264 @ 0x55b63e32c760] Unable to parse option value "fastpskip"
  
  [libx264 @ 0x55b63e32c760] Error setting option flags2 to value -fastpskip.

  How can I fix this to preserve motion at the cost of image quality ?

• FFmpeg - Multiple videos with 4 areas and different play times

  25 mai 2018, par Robert Smith

  I have videos as follows

  video   time
  
  ======= =========
  
  Area 1:
  
  video1a    0-2000
  
  video1b 2500-3000
  
  video1c 3000-4000
  
  
  
  Area 2:
  
  video2a  300- 400
  
  video2b  800- 900
  
  
  
  Area 3:
  
  video3a  400- 500
  
  video3b  700- 855
  
  
  
  Area 4:
  
  video4a  400- 500
  
  video4b  800- 900

  Basically these are security camera outputs and should display in 4 areas :

  So far I have the following :

  ffmpeg
  
      -i 1.avi -i 2.avi -i 3.avi -i 4.avi
  
      -filter_complex "
  
          nullsrc=size=640x480 [base];
  
          [0:v] setpts=PTS-STARTPTS, scale=320x240 [upperleft];
  
          [1:v] setpts=PTS-STARTPTS, scale=320x240 [upperright];
  
          [2:v] setpts=PTS-STARTPTS, scale=320x240 [lowerleft];
  
          [3:v] setpts=PTS-STARTPTS, scale=320x240 [lowerright];
  
          [base][upperleft] overlay=shortest=1 [tmp1];
  
          [tmp1][upperright] overlay=shortest=1:x=320 [tmp2];
  
          [tmp2][lowerleft] overlay=shortest=1:y=240 [tmp3];
  
          [tmp3][lowerright] overlay=shortest=1:x=320:y=240
  
      "
  
      -c:v libx264 output.mp4

  But there are two things I am missing :

  • The above is only for 4 video files, I need a way to add additional files to each area (for example video1b should play at its corresponding time after video1a in the same area)
  • How do I specify the beginning/ending time as shown above for each file ?

• lavfi/nlmeans : add SIMD-friendly assumptions for compute_safe_ssd_integral_image

  6 mai 2018, par Clément Bœsch

  lavfi/nlmeans : add SIMD-friendly assumptions for compute_safe_ssd_integral_image
  SIMD code will not have to deal with padding itself. Overwriting in that
  
  function may have been possible but involve large overreading of the
  
  sources. Instead, we simply make sure the width to process is always a
  
  multiple of 16. Additionally, there must be some actual area to process
  
  so the SIMD code can have its boundary checks after processing the first
  
  pixels.
  

  • [DH] libavfilter/vf_nlmeans.c