libaom v3.12.0 release candidate 1

[Wan-Teh Chang]

Hi everyone,

libaom v3.12.0 release candidate 1 is available. The release tag is
v3.12.0-rc1. Your testing will be greatly appreciated.

This release includes new codec interfaces, compression efficiency and
perceptual improvements, speedup and memory optimizations, and bug
fixes. This release is ABI compatible with the last release.

Five internal functions (aom_free, aom_malloc, aom_wb_bytes_written,
aom_wb_write_bit, aom_wb_write_literal) that were exported by mistake
are no longer exported from the libaom shared library. The removal of
these internal functions from the ABI is a bug fix and does not break
ABI compatibility.

Acknowledgments: The image quality optimizations in the new tuning
option AOM_TUNE_IQ were originally developed for SVT-AV1-PSY by
Cole Ogaard, Gianni Rosato, Julio Barba, and Zakaria Djebrouni.

- New Features
* New tuning option AOM_TUNE_IQ (image quality) for the
AOME_SET_TUNING codec control (--tune=iq) in all-intra mode. The
feature detection macro AOM_HAVE_TUNE_IQ, if defined, indicates
that AOM_TUNE_IQ is available.
* In all-intra mode, the AOME_SET_SHARPNESS codec control now also
sets the loop_filter_sharpness syntax element in the bitstream.
Larger values increasingly reduce how much the filtering can
change the sample values on block edges to favor perceived
sharpness.
* In all-intra mode, the default value of the AV1E_SET_QM_MIN codec
control is decreased to 4, and the default value of the
AV1E_SET_QM_MAX codec control is increased to 10. The default
values in good-quality and realtime modes remain unchanged (5 and
9, respectively).
* New value 3 for the AV1E_SET_ENABLE_CDEF codec control
(--enable-cdef): Enable CDEF adaptively based on frame qindex.
* New value 6 for the AV1E_SET_DELTAQ_MODE codec control
(--deltaq-mode): use modulation for all intra using Variance
Boost.

- Compression Efficiency Improvements
* Tuning mode AOM_TUNE_IQ improves image compression efficiency on
the CLIC dataset by up to 12% for the same SSIMULACRA 2 score, up
to 14% for the same DSSIM score, and up to 17% for the same
Butteraugli score.

- Perceptual Quality Improvements
* Adjust temporal filter strength for better visual quality.

- Speedup and Memory Optimizations
* Add the CDEF optimization for RISC-V.
* Help the compiler generate better vectorized code for variance
calculation and warped motion in generic CPU builds.
* Make several arrays const.

- Other Improvements
* Build: compile source files in parallel under MSVC.

- Bug Fixes
* Fix bug where metadata added with aom_img_add_metadata was lost
when frame scaling was used.

Thanks,
Wan-Teh Chang