[mythtv] Patch to autodetect 4:3 Zoom aspect ratio

aaron memoryguy at gmail.com
Thu Feb 28 14:05:08 UTC 2008

On 2/27/08, Mårten Bohlin <mabo at mochc.net> wrote:
> Hi! Thanks to everybody that tests this patch and are giving me feed back.
> I have adjusted it now so it should not be to picky about the 4:3
> aspect of the source video. And I have also added a cool debug mode
> that shows where detection is done. It also paints a black box in the
> top left corner that is the brightest version of black that is
> considered as black. (I can not see it on my screen since it looks
> totally black)


I tried this patch briefly last night (I'm getting home way too late
these days) and I can see that my problem with Stargate Atlantis
definitely is that the bars aren't dark enough. They sure looked black
until I saw the debugging square in the corner. I hesitate to increase
the threshold, though, because it might be getting light enough to
cause it to mis-detect.

I also found a funny quirk. Jeopary is always full-screen (not
letterboxed), but this patch consistently zooms in and out during
Final Jeopardy. Not a big deal, just kind of funny. :)  I think it's
because of black areas on the Jeopardy set being within range of the
detection code while the camera pans around. What happens is it comes
back from commercial, turns on zoom while they display the question,
then stays zoomed while they pan around and then when it passes a
certain point in the pan it turns off zoom. With debug mode enabled I
think I confirmed my suspicions about the detection: the ceiling and
floor of the set are dark enough that it thinks they're part of the

I'd have to guess that in order to get it really close to 100%
accurate you'd have to analyze the whole frame... which reminds me....
does the commercial detector have code to detect "aspect ratio
changes," including letterboxing? If that information is written to
the database, could it be leveraged here somehow?


"Oh oh oh. I'm incoherent with excitement. Please tell me what fascinating
bit of badger-sputumly inconsequential trivia you will assail me with next."
        -- Arthur Dent

More information about the mythtv-dev mailing list