[mythtv] 4:3 Zoom code changed?

Edward Wildgoose Edward.Wildgoose at FRMHedge.com
Wed Nov 12 12:47:12 EST 2003

> Your screen is 16 units wide and 12 high (for an aspect ratio of 4:3).   
> A widescreen frame inside this screen occupies an area 16 units wide  
> and 9 units tall.  A 4:3 frame inset within this widescreen frame  
> occupies an area 12 units wide and 9 units tall.  So to expand this  
> frame back to your full screen, we must blow it up by 4/3 and recenter  
> it.

This looks fine to me.  Specifically, if we expand it by 4/3 then we should get a final answer of 16 units by 12 units.

However, the picture on my 4:3 display is correctly 16 units wide, and an estimate 16 units tall (not 12 units tall).  This means that the tops of peoples heads are being cut off, and they become tall and thin.  However, the left and right is correctly clipping off just the black area.

I haven't checked the code, but I suspect a logic error which is causing scaling to be a bit large in the y axis?

I will try and have a poke through the code as well to see if I can pick it up.

> Oh, one final question... are the pixels in the video nonsquare?  Is  
> this BBC "widescreen" mode really anamorphic?  If this is the case, I  
> think I really do need the pixel and display dimensions of the various  
> parts in order to make sense of things.

Yes it is anamorphic, but its nothing special other than they always broadcast in 16:9, but they have a clever way to highlight the pan-n-scan area for viewers with 4:3 sets.  They publish the specs for they do this, but neither I nor anyone else have implemented this for Myth.  It's only really a problem in the case that the source material really is 4:3 in which case the black bars on the left and right look silly on the 4:3 set.  A set top box which understood the pan-n-scan algorithm would already have cropped it according to the broadcast instructions, and the broadcasters choice of 4:3 area would be filling the screen.

The raw video is usually 720x576 with a 16:9 aspect flag set.  Occasionally it is 704x576.  There are sometimes programs with these resolutions in proper 4:3 aspect ratio, but by far the most common is 16:9

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