[FFmpeg-devel] [PATCH] MMX VP3 Loop Filter
Mon Oct 6 10:03:14 CEST 2008
On Oct 6, 2008, at 3:42 AM, Jason Garrett-Glaser wrote:
> On Mon, Oct 6, 2008 at 12:35 AM, David Conrad <lessen42 at gmail.com>
>> On Oct 4, 2008, at 2:18 PM, Michael Niedermayer wrote:
>>> I'm not sure if this can be done with only 8-bit math;
>>> filter_limit can
>> theoretically be 127 which pushes CONST0/1 to +- 254, and mm2/mm3
>> can range
>> from -127 to 128.
> Are you sure filter_limit can be that large? I know of no sane
> deblocker that allows such high limit values.
Quoting the Theora spec,
LFLIMS - Integer array - 7 bits - Not signed
This procedure decodes the table of loop ?lter limit values used to
loop ?lter, which is described in Section 6.4.1. It is decoded as
1. Read a 3-bit unsigned integer as NBITS.
2. For each consecutive value of qi from 0 to 63, inclusive:
(a) Read an NBITS-bit unsigned integer as LFLIMS[qi ].
I can't find anything in the spec that limits it any further.
> Even if it can, you can still do it in byte math; look at x264's
> deblocking code for reference. H.264 requires 9 or 10 bits of
> precision for various parts of deblocking, and x264 gets away with
> using byte math by emulating the extra bits separately. This is still
> faster than unpacking and doing 16-bit math.
I'll have a look; at the very least I guess I could only do 16-bit
math in the unlikely extreme cases.
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