libaom v3.13.0 release candidate 1

[Wan-Teh Chang]

Hi everyone,

libaom v3.13.0 release candidate 1 is available. The release tag is
v3.13.0-rc1. Your testing will be greatly appreciated.

This release is ABI compatible with the last release.

The aom_roi_map_t struct, used only by the codec control
AOME_SET_ROI_MAP, was modified in this release. Since AOME_SET_ROI_MAP
was unimplemented, aom_roi_map_t was effectively an unused struct.
Therefore aom_roi_map_t is to be considered as a new struct added in
this release and this change does not break ABI compatibility.

- New Features
* New tuning mode AOM_TUNE_SSIMULACRA2 for the AOME_SET_TUNING codec
control (--tune=ssimulacra2) in all-intra mode. The feature
detection macro AOM_HAVE_TUNE_SSIMULACRA2, if defined, indicates
that AOM_TUNE_SSIMULACRA2 is available. AOM_TUNE_SSIMULACRA2 was
developed to maximize SSIMULACRA 2 scores.
* New codec control AV1E_SET_SCREEN_CONTENT_DETECTION_MODE
(--screen-detection-mode).
This codec control helps select between two screen detection modes:
- Mode 1: standard (default)
- Mode 2: anti-aliased text and graphics aware
* New codec control AV1E_SET_ENABLE_ADAPTIVE_SHARPNESS
(--enable-adaptive-sharpness). When enabled, it modulates sharpness
based on frame QP, which helps mitigate blocking artifacts in the
low to medium quality range.
* Added low complexity mode for 720p vertical videos.
* ROI feature implemented for RTC: for delta QP, skip encoding, and
reference selection.
* External scaling feature for SVC: allow downscaled images to be
passed into encoder for spatial layers without reconfiguring it.
* Allow per-frame calculation of PSNR (contribution from Meta).

- Compression Efficiency Improvements
* Variance Boost is now enabled for tuning modes AOM_TUNE_IQ and
AOM_TUNE_SSIMULACRA2 at speeds 8 and 9 (2-5% SSIMULACRA 2 BD-Rate
gains)
* Several quality/time tradeoff improvements and bug fixes for all
intra mode speeds 8 and 9.
* Up to 6.9% SSIMULACRA 2 BD-Rate gains for speed 8
* Up to 2.2% SSIMULACRA 2 BD-Rate gains for speed 9

- Perceptual Quality Improvements
* RTC: Visual quality improvements for screen content mode.
* RTC: Visual quality improvements for video mode for resolutions >=
720p.

- Speedups
* Optimize intraBC search for better speed/efficiency tradeoffs for
all intra mode speeds >= 1
* Optimize intraBC block hashing process
* RTC Screen: speed feature added to speed 12 for ~2x speedup on
slide/scene changes, for resolutions >= 720p.
* ML based speedup improvement on the partition pruning for speed <= 2

- Other Improvements
* Fixes for RPS (reference picture selection) for RTC: Based on
av1_discuss issue:
https://groups.google.com/a/aomedia.org/g/av1-discuss/c/sqFad980SsA

- Bug Fixes
* b:421196988: all intra speed 8: overuse of palette mode
unnecessarily inflating file sizes
* b:423804955: Improve quality for 4K Screencast
* webrtc:388070060: Allow per-frame calculation of PSNR
* b:433046392, b:432035817: Fix to SVC crash triggered with Jitsi
video conference app.
* b:419622699: Fix integer overflow in update_buffer_level
* b:407813259: Fix to update seq_params for number of layers change
* b:400885218: External scaling for AV1
* b:391849810: High AV1 frame encode time on slide changes
* b:399575647: Too aggressive QP backoff at scene changes
* b:383306740: Quality degradation at horizontal scrolling

Thanks,
Wan-Teh Chang