[FFmpeg-devel] [PATCH] aac: smal fix in aacpsy pe reduction step

[Claudio Freire]

This is a small patch, but it does have a big impact on bit allocation.

Measured with the attached scripts (in case someone might find them
useful), all the regressions marked in the report have no audible
difference (I didn't check them all though), but the improvements can
be heard.

This affects mostly high bit rates. It's related to issue #2686.

In the report, A is the patched version, B is unpatched, all
comparisons show deltas in the form (A-B), so a positive pSNR delta
means a better quality in the patched version, and negative a
regression. Regressions are only considered for pSNR deltas below
-1db, they're considered serious below -6db.

All measurements were done with tiny_psnr.

The summary of the report inline for quick reading:

Files: 58
Bitrates: 6
Tests: 347
Serious Regressions: 0 (0%)
Regressions: 10 (2%)
Improvements: 54 (15%)
Big improvements: 26 (7%)
Worst regression - sine_tester.flac - 384k
  - StdDev: 1.68        pSNR: -3.05     maxdiff: -178.00
Best improvement - 07 - Bound.flac - 384k
  - StdDev: -1700.05    pSNR: 20.64     maxdiff: -29595.00
Average          - StdDev: -55.67       pSNR: 1.20      maxdiff: -1593.00
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