[FFmpeg-devel] [PATCH] Make VP3/Theora Decoder Much Faster

Jason Garrett-Glaser darkshikari
Mon Dec 7 18:22:38 CET 2009

On Mon, Dec 7, 2009 at 8:28 AM, Loren Merritt <lorenm at u.washington.edu> wrote:
> On Mon, 7 Dec 2009, Mike Melanson wrote:
>> I'm a little surprised to realize that this functionality doesn't already
>> exist (been a long time since I wrote the decoder). The original VP3 decoder
>> had IDCTs for 1- and 3-element fragments in addition to the full flavor
>> IDCT. I think perhaps I tried to bring them over but someone convinced me
>> that those other cases don't occur often enough to make it worthwhile. Have
>> you found a lot of fragments with 1-3 non-zero coeffs?
> I've never examined a Theora bitstream, and I'm not about to start now.
> However, if Theora doesn't have lots of DC-only blocks, it's either very
> different from every other inter-predicted DCT codec out there, or you're
> encoding at a ridiculously high bitrate.
> I don't remember why I never committed such a change to mpegvideo, but it's
> not that it didn't help. Maybe this isn't bitexact and I never bothered to
> figure out why?

Well, it certainly helped a heck of a lot on VC-1.  And from what I
recall, the official Theora encoder does no decimation whatsoever on
DC coefficients, which would result in a lot of blocks, especially
inter, with DC coeffs only.

Dark Shikari

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