Log Message:
x265: updated to 2.8

Version 2.8

New features
1. :option:--asm avx512 used to enable AVX-512 in x265. Default disabled.
    For 4K main10 high-quality encoding, we are seeing good gains; for other \ 
resolutions and presets, we don't recommend using this setting for now.

2. :option:--dynamic-refine dynamically switches between different inter refine \ 
levels. Default disabled.
    It is recommended to use :option:--refine-intra 4' with dynamic refinement \ 
for a better trade-off between encode efficiency and performance than using \ 
static refinement.

3. :option:--single-sei
    Encode SEI messages in a single NAL unit instead of multiple NAL units. \ 
Default disabled.

4. :option:--max-ausize-factor controls the maximum AU size defined in HEVC \ 
specification.
    It represents the percentage of maximum AU size used. Default is 1.

5. VMAF (Video Multi-Method Assessment Fusion)
   Added VMAF support for objective quality measurement of a video sequence.
   Enable cmake option ENABLE_LIBVMAF to report per frame and aggregate VMAF \ 
score. The frame level VMAF score does not include temporal scores.
   This is supported only on linux for now.

Encoder enhancements
1. Introduced refine-intra level 4 to improve quality.
2. Support for HLG-graded content and pic_struct in SEI message.

Bug Fixes
1. Fix 32 bit build error (using CMAKE GUI) in Linux.
2. Fix 32 bit build error for asm primitives.
3. Fix build error on mac OS.
4. Fix VBV Lookahead in analysis load to achieve target bitrate.