--- On Thu, 10/7/10, Burkhard Plaum <pl...@ipf.uni-stuttgart.de> wrote:
> From: Burkhard Plaum <pl...@ipf.uni-stuttgart.de>
> Subject: Re: [CinCV] need clarification of user-manual comment
> To: cinelerra@skolelinux.no
> Date: Thursday, October 7, 2010, 5:23 AM
> Hi,
>
> Am 07.10.2010 00:22, schrieb anyeos:
> >
> > It applies not only for OpenGL instead in video in
> general. There are
> > some encoders that can only work in some width or
> height multiples, like
> > 4.
>
> The usual 4:2:0 sampling requires that dimensions are
> multiples of 2. It's
> theoretically possible to support odd dimensions, but they
> many programs fail here.
>
> Usual compression methods work on 16x16 blocks internally,
> but all these
> codecs allow arbitrary *even* dimensions. They just pad the
> images internally.
> I'm not aware of any mainstream codec, which requires
> multiples of 4.
>
> > So you can have: 320x240, 420x480, 640x480, and so,
> all divisible by
> > 4. Take care too about the aspect ratio what it is
> width/height in the
> > example of 420/480 it is 0,875 not an standard one
> (640/480 get 1,333333
> > or 4:3, 320x480 the same, 720/480 is 16:9 or 1,7777777
> standard NTSC and
> > so).
>
> You also have nonsquare pixels. All modern codecs store the
> pixel aspect
> ratio instead of the display aspect ratio.
>
> Burkhard
I read in mencoder documentation years ago that the codecs required the 16x16
blocks. that is partly why I was confused about what the cinelerra document
said regarding the (size) of the project tracks...That really should be updated
in the user-guide to be more explicit...and based on the discussion it has
sparked, perhaps the developers need to reexamine the requirement and publish
the real (current) requirement. :^)
I'm working with 720p and 480p vertical but want to maintain close to a 16:9
aspect. 720p works ok at 1280x720 but 480 need 854 horizontal to achieve the
correct aspect...I end up scaling to 848x480 to maintain the divisible by 16
constraint...that is acceptable...
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