Recherche avancée

Sur d’autres sites (7360)

• aarch64 : vp9mc : Load only 12 pixels in the 4 pixel wide horizontal filter

  3 janvier, par Janne Grunau

  aarch64 : vp9mc : Load only 12 pixels in the 4 pixel wide horizontal filter
  This reduces the amount the horizontal filters read beyond the filter
  
  width to a consistent 1 pixel. The data is not used so this is usually
  
  not noticeable. It becomes a problem when the application allocates
  
  frame buffers only for the aligned picture size and the end of it is at
  
  a page boundary. This happens for picture sizes which are a multiple of
  
  the page size like 1280x640. The frame buffer allocation is based on
  
  its most likely done via mmap + MAP_ANONYMOUS so start and end of the
  
  buffer are page aligned and the previous and next page are not
  
  necessarily mapped.
  
  Under these conditions like seen by Firefox a read beyond the end of the
  
  buffer results in a segfault.
  
  After the over-read is reduced to a single pixel it's reasonable to use
  
  VP9's emulated edge motion compensation for this.
  Fixes : https://bugzilla.mozilla.org/show_bug.cgi?id=1881185
  
  Signed-off-by : Janne Grunau <janne-ffmpeg@jannau.net>
  
  Signed-off-by : Ronald S. Bultje <rsbultje@gmail.com>
  

  • [DH] libavcodec/aarch64/vp9mc_neon.S

• Fast accurate video trim like Instagram using FFmpeg Android

  11 août 2016, par dan87

  I know it’s been asked before but I couldn’t find a fast and accurate solution yet, I want to trim videos with a maximum lenght of 15 seconds. Here is what I’ve tried so far, I’m working with this video as example :http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_30mb.mp4

  The fastest way

  This is by far the fastest way because it doesn’t need to re-encode the video but it’s very innacurate in this video because the key frames are every 5-10 seconds :

  ffmpeg -i SampleVideo_1280x720_30mb.mp4 -ss 30 -to 50 -c copy -y out.mp4

  Here is how I check the key frames in this video :

  ffprobe -select_streams v -show_frames -show_entries frame=pict_type -of csv SampleVideo_1280x720_30mb.mp4 | grep -n I | cut -d ':' -f 1

  With this command I found out that the second key frame it’s in the 211th frame which means 210 frames between the first key frame and the second, knowing that it’s a 25fps video it would be around 8 seconds between the key frames, so any cut between 1-8 seconds would fall in one of this frames which is a huge difference for a 15 seconds video.

  The accurate way

  This way it’s accurate but it requires to re-encode the video :

  ffmpeg -i SampleVideo_1280x720_30mb.mp4 -ss 30 -to 50 -preset ultrafast -y out.mp4

  The problem is this command takes more than 20 seconds to finish using the ultrafast preset, in a samsung galaxy s6 edge plus which probably would be much more in other devices.

  Nevertheless, if I open the SampleVideo_1280x720_30mb.mp4 in Instagram and trim it they get an accurate trim in less than 2 seconds.

  I also tried to force the keyframes every second, but it also requires to re-encode the video and it affects the video quality :

  ffmpeg -i SampleVideo_1280x720_30mb.mp4 -force_key_frames "expr:gte(t,n_forced*1)" out.mp4

  Does anybody know how Instagram trim the videos or a way to get a fast and accurate trim with FFMpeg ?

• avcodec : add emuedge_linesize_type

  4 septembre 2013, par Michael Niedermayer

  avcodec : add emuedge_linesize_type
  Currently all uses of the emu edge code as well as the code itself
  
  assume int linesize
  
  changing some but not changing all would introduce a security issue
  
  once all use this typedef a simple search and replace can be
  
  done to switch them all to ptrdiff_t
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/mpegvideo_motion.c
  • [DH] libavcodec/videodsp.h
  • [DH] libavcodec/videodsp_template.c
  • [DH] libavcodec/x86/videodsp_init.c