[FFmpeg-devel] [PATCH 0/3] AC3 fixed-point encoder sample shifting

[Michael Niedermayer]

On Tue, Mar 08, 2011 at 01:21:43PM -0500, Justin Ruggles wrote:
> On 03/08/2011 01:18 PM, Justin Ruggles wrote:
> 
> > 
> > This patch set changes how and when the fixed-point encoder does sample 
> > value shifting.  Currently it left-shift normalizes samples to 16-bit in 
> > each block for each channel, then adjusts the exponents accordingly so 
> > that the final coefficient scale will be correct.  With the addition of 
> > channel coupling, it now becomes important to have greater than 16-bit 
> > accuracy in the coefficients.  The floating-point encoder converts the 
> > coefficients to 25-bit fixed-point since that is the internal scale for 
> > AC3.  This patch does the same for the fixed-point encoder by shifting 
> > the coefficients back to their original scale, but in the 25-bit range.
> > 
> > Patch 1 is needed to handle the higher coefficient scale in channel 
> > coupling.
> > 
> > Patch 2 is what I describe above.
> > 
> > Patch 3 adds x86 SIMD optimization for both pre-MDCT and post-MDCT 
> > shifting.
> > 
> > Total encoding time:
> > current: 4.16s
> > patch 1: 4.16s
> > patch 2: 4.07s
> > patch 3: 4.01s
> > 
> > Justin Ruggles (3):
> >   ac3enc: use MUL64() to multiply fixed-point coefficients
> >   ac3enc: shift coefficients to 24-bit following MDCT rather than using
> >     an     exponent offset.
> >   ac3enc: add SIMD-optimized shifting functions for use with the
> >     fixed-point AC3     encoder
> 
> 
> I forgot something... PEAQ comparison.
> 
> http://www.flickr.com/photos/justinruggles/5431711148/

great work, all commited will push later

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There seems to be only one solution to NIH syndrom, ... a shooting squad
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