[FFmpeg-devel] [PATCH 0/3] AC3 fixed-point encoder sample shifting
Tue Mar 8 19:21:43 CET 2011
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
> Patch 2 is what I describe above.
> Patch 3 adds x86 SIMD optimization for both pre-MDCT and post-MDCT
> 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.
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