[M4IF Technotes] MPEG4 Visual: Aspect Ratio

[Rob Koenen]

I never ssaw an answer to this question.
You are right in stating that conformant decoders MUST be able
to decode these 'other' aspect ratios. Do the decoders out there
indeed decode them? that's up to the decoder manufacturers to
answer.
The standard, however, prescribes nothing about display. So 
the decoded picture may not fit on your display, or you may
give the user the option to pan. On a computer display, you can
actually do pretty neat things with 'other' display ratios
(and with the option to have multiple objects for that matter)
Rob
> -----Original Message-----
> From: Christoph Stadler [mailto:Christoph.Stadler   dynapel.de]
> Sent: Friday, February 22, 2024 9:13
> To: technotes   lists.m4if.org
> Subject: [M4IF Technotes] MPEG4 Visual: Aspect Ratio
> 
> 
> 
> Dear M4IF community,
> 
> I have a question concerning the pixel aspect ratios used in
> MPEG-4 Visual:
> 
> The bitstream syntax allows to either use one of the pre-defined
> pixel aspect ratios (e.g. 12:11 or 40:33) or to explicitly specify 
> a private one by setting 'aspect_ratio_info:=extended_PAR'. 
> This allows to transmit any aspect ratio that can be represented 
> as a fraction p:q with p,q in [1;255].
> 
> Although this sounds to me like a nice and possibly very helpful 
> feature, I somewhat hesitate to use it in a real encoder, as I fear
> that the (unspecified) decoder - or its attached compositor/display 
> unit - will not be able to handle these arbitrary values. 
> 
> Of course this would imply that the decoder/compositor is not fully 
> conformant, but if it works properly with all the other encoders which
> use only the standard aspect ratios, my position could turn 
> out rather 
> weak.
> 
> Does anyone of you have experiences confirming or dispersing my 
> worries ?
> 
> Thank you in advance,
> 
> 	Christoph Stadler
> 
> 
> ---------
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