libaom v3.2.0 release candidate 2

[Wan-Teh Chang]

Hi everyone,

libaom v3.2.0 release candidate 2 is available. The release tag is
v3.2.0-rc2. Your testing will be greatly appreciated.

Compared with release candidate 1, release candidate 2 cherry-picked
the following five changes:

Define the AOM_NO_RETURN macro for MSVC
https://aomedia-review.googlesource.com/c/aom/+/145841

Issue 3161: unresolved symbol aom_codec_av1_cx_algo when building with
-DBUILD_SHARED_LIBS=1 on Windows
https://aomedia-review.googlesource.com/c/aom/+/146842

AV1 RT: Fix uninitialized variable use in estimate_intra
https://aomedia-review.googlesource.com/c/aom/+/147024

Fix a bug in av1_quantize_lp AVX2 optimization
https://aomedia-review.googlesource.com/c/aom/+/146523

Fix uninstantiated FullPrecisionQuantizeLpTest
https://aomedia-review.googlesource.com/c/aom/+/146602

Here is the current draft of the release notes:

This release includes compression efficiency and perceptual quality
improvements, speedup and memory optimizations, as well as some new
features.

- New Features
* Introduced speeds 7, 8, and 9 for all intra mode.
* Introduced speed 10 for real time mode.
* Introduced an API that allows external partition decisions.
* SVC: added support for compound prediction.
* SVC: added support for fixed SVC modes.

- Compression Efficiency Improvements
* Intra-mode search improvement.
* Improved real time (RT) mode BDrate savings by ~5% (RT speed 5)
and ~12% (RT speed 6). The improvement was measured on the video
conference set.
* Improved real time mode for nonrd path (speed 7, 8, 9): BDrate
gains of ~3-5%.
* Rate control and RD adjustments based on ML research in VP9.
Modest impact for low resolution but ~0.5-1.0% for HD.

- Perceptual Quality Improvements
* Added a new mode --deltaq-mode=3 to improve perceptual quality
based on a differential contrast model for still images.
* Added a new mode –deltaq-mode=4 to improve perceptual quality
based on user rated cq_level data set for still images.
* Weighting of some intra mode and partition size choices to better
manage and retain texture.

- Speedup and Memory Optimizations
* Further improved 2-pass good quality encoder speed:
o Speed 2 speedup: 18%
o Speed 3 speedup: 22%
o Speed 4 speedup: 37%
o Speed 5 speedup: 30%
o Speed 6 speedup: 20%
* Optimized the real time encoder (measured on the video conference
set):
o RT speed 5 speedup: 110%
o RT speed 6 speedup: 77%

- Bug Fixes
* Issue 3069: Fix one-pass mode keyframe placement off-by-one error.
* Issue 3156: Fix a bug in av1_quantize_lp AVX2 optimization.

Thanks,
Wan-Teh Chang