[mythtv] New AspectRatio option

Terry Barnaby terry1 at beam.ltd.uk
Thu Dec 2 11:44:19 UTC 2004


Ed Wildgoose wrote:
> 
>> I am using an M10K box with Fedora 2 and have set the "DisplaySize"
>> option to "400 225" which seems to work fine for me, apart
>> from the OSD which I know has been fixed. My MythTv is
>> from CVS on 21/11/04.
> 
> 
> 
> Nice to know.  What is your screen res with these settings?  720x576 as 
> stated below?
> 
> Do all the fonts look OK for you on the various screens?  With my 
> settings I find them a bit too large? Your settings appear to give a dpi 
> around 50-65 (depending if you look horizontally or vertically)
> 
> 
>> With the M10K set to 720x576, DisplaySize not given and the
>> test video which is a 720x576 interlaced video, running
>> "mythtv <videofile>" gives good output which is interlaced.
>> MythTv is not scaling the incoming video, which is correct.
>> However, if I change the aspect ratio with the "w" command
>> and go back to "4:3" mode (or use the appropriate configuration 
>> setting to force 4:3 mode initially"), then the displayed video no
>> longer looks correctly interlaced.
>> I haven't looked into this yet, maybe some different scaling
>> is applied when the "w" command is used to swap aspect ratio.
> 
> 
> 
> Hmm, I haven't dug in to find the relevant code, but from the 
> description I would guess that it could be a bug due to starting with 
> the width to get the height, or starting with the height to get the 
> width, etc..?  I guess if you could locate the relevant calculation and 
> add some debugging code then you would see some small rounding error 
> that would clearly show the problem?
> 
> If I get a chance I will have a look myself because I have exactly the 
> same issue.  Would also be interested to locate the same code in mplayer 
> to tune that as well!
> 
> Interesting stuff.
> Thanks
> 
> Ed W
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My screen res is 720x567 to match the UK DVB-T PAL picture. I have
turned off all scaling of the MPEG2 video stream to get the best
picture quality. Any scaling in use is bad on TV's.

The fonts look Ok at the various screens with the DisplaySize I choose.
However, I would have thought that it would be much better if MythTV
would set the fonts based on the Pixel resolution rather than screen size.
For TV's entering a correct screen size for a Plasma 42inch would result in
micro fonts .... In that case of TV output you want the fonts to be scaled
relative to the overal picture.

I will have a look at the code when I have the chance as well ....

I have some info on setting up the Unichrome Driver for the M10K to get good
quality TV output at: http://www.kingcot.eclipse.co.uk/unichrome/unichromeTvOut.html
if you are interested.

Terry


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