Re: [V4L] V4L2 - RFC: DMA to userspace API

[Gerd Knorr]

> I have seen some mmx filters, and even some hardware, that requires the
> lines to be DWORD or QWORD aligned.

No problem with the common image sizes, lines will be aligned even
without any padding:

NTSC: 640 = 2^7 * 5
PAL:  768 = 2^8 * 3

The common DCT-based compression algorithms want image width be
a multiple of 8 or 16 because the DCT blocks are 8x8 (luma needs
to be 16 then because of chroma subsampling).  That will give
you qword aligned lines without padding too.

> Granted, this is rare,

... and would be a problem only if you want to use image sizes
like 389 * 251.  Is this really a problem?

  Gerd

-- 
Get back there in front of the computer NOW. Christmas can wait.
        -- Linus "the Grinch" Torvalds,  24 Dec 2000 on linux-kernel



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