[theora-dev] ffmpeg2theora aspect ratio

Lino Mastrodomenico l.mastrodomenico at gmail.com
Sat Dec 5 12:32:52 PST 2009

2009/12/4 Stefan Bender <oraqhf at gmx.net>:
> FWIW, it didn't change any encoding parameters;
> it just prevented e.g. mplayer to automatically scale 720x576
> theora content to the correct 768x576 (for 4:3 frame aspect)

Sorry for nitpicking, but the 4:3 or 16:9 aspect for PAL content isn't
for the whole 720x576 frame: it's the aspect ratio of the 702x576
active area. Which means that the overall aspect ratio for PAL frames
is 160:117 (for "4:3" content) or 640:351 (for "16:9" movies).

I.e. they should played at approximately 788x576 or 1050x576
respectively (not 768x576 or 1024x576 as most software players do).

Similarly for NTSC videos the active area to which the 4:3 or 16:9
aspect ratio should be applied is exactly 710.85x486 pixels (I kid you
not). So the final aspect ratio of the 720x480 NTSC frame is exactly
6480:4739 or 8640:4739 (respectively for "4:3" or "16:9" content).

A complete guide to all this aspect ratio madness is:

If you still have doubts try playing e.g. a movie with the "Universal"
logo at the beginning: on your TV with a good old hardware DVD player
the Earth will be a perfect circle, while a software player on a
computer will almost certainly display it as an ellipse, slightly
higher than its width.

And, yes, I can easily tell the difference between Alyson Hannigan at
768x576 and at 788x576.


Lino Mastrodomenico

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