On Thu, 16 Oct 2003, Matto Marjanovic wrote:
> None of them --- those are all packed formats, and the permutations of
> letters describe different packings, not different subsamplings.
True - I knew they were not distinct subsamplings. What was
unknown was which packing is needed for y4mscaler (planar is
the answer of course ;)).
> As I have kvetched before, FourCC's are so lacking in meaning as to be
> practically irrelevant. fourcc.org only lists one code which possibly
> denotes a planar 4:2:2 mode, with the dubious description:
>
> Y42B - Weitek format listed as "YUV 4:2:2 planar".
> I have no other information on this format.
Apple has some very good information about video packings,
encoding, and of course Quicktime. They also have some
confusing information (you wondered where I got the idea
that chroma samples are "shared"? Apple.)
Is this better?
From http://developer.apple.com/quicktime/icefloe/dispatch020.html
k2vuyPixelFormat
'2vuy'
8-bit 4:2:2 Component YCbCr format. Each 16 bit pixel is represented by an
unsigned eight bit luminance component and two unsigned eight bit chroma
components. Each pair of pixels shares a common set of chroma values. The
components are ordered in memory; Cb, Y0, Cr, Y1. The luminance components
have a range of [16, 235], while the chroma value has a range of [16, 240].
This is consistent with the CCIR601 spec. This format is fairly prevalent
on both Mac and Win32 platforms. The equivalent Microsoft fourCC is UYVY.
kYUVSPixelFormat
'yuvs'
8-bit 4:2:2 Component YCbCr format. Identical to the k2vuyPixelFormat except
each 16 bit word has been byte swapped. This results in a component ordering
of; Y0, Cb, Y1, Cr. This is most prevalent yuv 4:2:2 format on both Mac and
Win32 platforms. The equivalent Microsoft fourCC is YUY2.
> Getting back to y4mscaler, no matter what the subscaling is, the input
> is planar Y'CbCr, with the planes presented in that order. The 4:2:2
Ok, so if I pursue the current itch I'll need a YUY2 to planar
conversion program. Easy enough.
> > Hmmm, the next question would be how complete the support is for
> > 422 in mpeg2enc but that can wait for another night <grin>
>
> Do any consumer hardware MPEG players support 4:2:2 profiles? I know
> they exist in the standard, but from what I remember reading, they
Almost certainly not consuer and I doubt even 'pro-sumer'
hardware would handle it.
TV studios use 10bit 4:2:2 for everything and it gets downsampled
to 420 just before going out the transmitter.
Playback on a computer shouldn't be a problem though.
> sure where you would play them even if mpeg2enc would compress them
> for you.
There is some logic in mpeg2enc for it but I have no idea how
complete it is. Definitely not worth spending a lot of time
on.
As I mentioned - an idle question ;)
Thanks for the info.
Steven Schultz
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