Bad PAR presets.

[RadicalEd]

XviD's PAR presets have been calculated incorrectly using 704x as a basis for all PARs. Here's a correct table

system____padded____real______DAR_______PAR__
PAL_______720x576___702x576___4:3_______128/117
PAL_______720x576___702x576___16:9______512/351
NTSC______720x480___711x486___4:3_______72/79
NTSC______720x480___711x486___16:9______96/79

Man those tabs are annoying :|

Using 704x as a basis makes sense for resizing before encoding, but it should should be safe use the true PAR when dealing with resize-on-playback kind of stuff, no?

[Koepi]

The PAR presets are directly taken from mpeg4 standard.
It's close related to the presets of MPEG2.

So the mpeg standard is flawed in itself according to your findings.

(Sorry, but you should use "correct" input ratios, and calculate depending on that the correct output ratios. It's a hell of a job to make this AR stuff simple and understandable. I think I understand the point you're trying to make, but your assumption is based on wrong preconditions IMO.)

Please forward that post to the MPEGLA and tell them they're wrong :)

Regards
Koepi

[RadicalEd]

Ah, I wasn't aware specific ratios were defined in the standard. I suppose that comes into play with hardware devices. Seems mpeg would rather stick with mod16 digital pseudo-standard compatibility over PAR accuracy. In that case, either some distortion accounting-for will have to be done in preproduction, or imperfect AR will have to be accepted :|

Oh well, there's always the custom field :D

Btw, I doubt this matters, but 47/20 is the lcm version of 2.35 (as opposed to 235/100).

GCM->LCM*