[FFmpeg-user] OT(?) - ffmpeg speed of subtitle generation, vlc Vs mythtv

Nicolas George george at nsup.org
Thu Mar 12 10:56:13 CET 2015

Le duodi 22 ventôse, an CCXXIII, Kingsley Turner a écrit :
> My daughter made some karaoke-like videos with a bunch of colour-changing
> lyric-subtitles into MKV files (with fonts embedded).

That would be ASS subtitles then.

> As far as I know, both VLC and MythTV use ffmpeg for the rendering of the
> video frames.

For the decoding of the video frames. For the rendering of the subtitles
elements, they certainly use libass, and for the overlaying of the subtitles
elements and the rendering of the frames to screen, they use their own code
or other libraries.

I have noticed (with MPlayer) that libass can be weirdly slow, weirdly
because between rendering at 1280×720 and at 1920×1080, the rendering can go
from perfectly real-time to very very slow, much more than the ×2.25 factor
for the number of pixels.

I have not yet had the courage to investigate.


  Nicolas George
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