--- 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... _______________________________________________ Cinelerra mailing list Cinelerra@skolelinux.no https://init.linpro.no/mailman/skolelinux.no/listinfo/cinelerra