[mythtv-users] SOLVED: SRT subtitle rendering causes stuttering

[Jim Stichnoth]

On Wed, Aug 21, 2013 at 1:02 PM, Jim Stichnoth <stichnot at gmail.com> wrote:

> It does take longer to render larger subtitles, hence the difference you
> see with subtitle zoom.  It also gets a lot worse when you use outlinesize.
>  The way things are implemented in MythUI, if your outlinesize is N, the
> outline is created by drawing 8N separate copies of the text.  (This is the
> number of pixels in the perimeter of a square with edge length 2N+1.)  It
> may not be quite this bad, though, if the MythUI image cache is getting
> involved.  If I had thought about this earlier, I would have advised
> caution with using outlinesize.
>
> FWIW, for post-0.27 I'm looking into ways of spreading the subtitle work
> across multiple video frames to lessen the possibility of stuttering.
>

I spent a little more time investigating the performance.  Using
outlinesize indeed seems to have a linear impact on drawing time.  But
surprisingly, on my system, there was a vast performance difference between
100% and 150% subtitle zoom factor.  (Those were the only two zoom factors
I tried.)  A zoom of 150% was 15 to 25 times as expensive to draw as 100%,
even though in theory there are only 2.25 times as many pixels to draw.  My
only guess is that certain (expensive) hints in the TrueType description
were only applied for higher point sizes.  This would presumably depend on
the font (MythTV-supplied FreeMono in my case) and the display resolution
(1600x900 in my case).  There are probably other aspects of the system and
of the MythTV configuration that come into play as well.

Jim
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