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2013-01-14, 13:02
(This post was last modified: 2013-01-14, 13:02 by popcornmix.)
The main problem with this approach is most composite displays only accept either PAL or NTSC (possibly displaying the wrong one in monochrome).
There is no way to query from display if this will work or not (unlike hdmi).
I think implementing this will generate a lot of support issues of "some videos play with black screen".
Does xbmc support PAL/NTSC composite framerate switching on any other platforms?
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I'm not actually sure whether it's necessary or desirable to switch between PAL/NTSC or if it would be better to switch from PAL50 to PAL60, as it's just to match the refresh rate to the video to avoid micro-stutter.
As the Pi supports PAL60 I imagine it is possible between them on the fly and then it's just switching refresh rate and not resolution.
The only possible issue is a mismatch between colourspaces if the video is coded for NTSC colourspace and the TV is using PAL colourspace. I guess TVs that support both PAL and NTSC automatically adjust their colourspace when switching to match the material. I'm not sure how noticeable it would be if it's playing NTSC material into a PAL colourspace though, so it might not be significant enough to worry about.
Interesting to see that resolution switching is being looked at for HDMI at least though.
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There is no PAL60 or NTSC50 over composite. It just doesn't exist as a standard.
PAL is 50 fields per second 720x576 (overscanned).
NTSC is 60 fields per second 720x480 (overscanned).
You can't change the framerate without changing the resolution.
In the video file, they both use the same colourspace (ITU-R Rec. BT.601). There is nothing to convert.
(sure the analogue signal over composite cable represents colour differently for PAL/NTSC, but if the TV supports both, then it will do the right thing).
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OK, thanks for clarifying that. So we just need to switch between PAL and NTSC somehow.
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Just wondering if there's been any further consideration of a way to facilitate auto-switching, perhaps using the tvservice command, of the composite output between PAL and NTSC depending on the video framerate?
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currently, i have a few Pis, at this stage running raspbmc. i know for a fact, that the only display option to me is ghosted on NTSC (Never Twice the Same Colour), and my old telly only displays mono.
however, a method that i think some tv card manufacturers use to try and determine framerate is via the region settings.
i.e. if region is set to Australia, composite will be PAL 50hZ, whereas, if region is set to a USA state, then you could safely assume NTSC 60hZ.
D.