[mythtv-users] MHEG issues (UK) - flickering, video resizing, mind the gaps!

[Mark Kendall]

On 06/04/2008, Sam Jacobs <samlists at ijacobs.co.uk> wrote:
> Hi all,
>
>  I've noticed a few issues with MHEG, and couldn't find any posts on
>  them, so here they are, in no particular order:
>
>  2. When an app requests video to be rendered quarter-screen, the
>  frontend actually decodes and renders a copy of the same video stream
>  (CPU usage about doubles, but network activity stays the same). While
>  this probably isn't an issue on reasonably powerful frontends with SD
>  video (on my Mac, CPU usage is about 40% normally, and 80% when on a
>  BBCi page displaying 1/4-screen), it isn't very efficient and I'd
>  imagine things would suffer greatly with HD video.

The frontend does not decode the stream twice (although it might look like it!).

When you're using straight XVideo as the renderer, the video frame is
the only thing that is displayed on the screen. The osd, PiP etc are
all blended into the frame in software before it is displayed. The
MHEG screens are also rendered as an OSD (and hence are blended into
the frame) and when the video stream is shown half/quarter size etc,
it is done using very similar code to that used to render the PiP -
the frame is scaled to a given size and blended into 'itself'. You
could clear the  rest of the video information but if the MHEG 'osd'
is rendered correctly then it is unnecessary.

>  3. The gaps! Obviously, it must be difficult to get everything laid
>  out correctly, and the engine does a great job at the moment, but
>  because of 2 the gaps are really obvious because the fullscreen video
>  shows through them!