Summarized changelog:

• Improvements:
  • Enable open partitions on frame boundaries (2% improvement to coding efficiency).
  • Enable deblocking in loop filter rate-distortion optimization (0.5% to 1.5% improvement to coding efficiency).
  • Add monochrome support.
  • Improve 4:2:2 support (37% reduction in encoding time, 0.8% to 5% improvement to coding efficiency).
  • Support arbitrary-SAR anamorphic video.
  • Enforce a frame limit of 1 in still picture mode.
  • Update non-broken motion estimation predictors (0.28% improvement to coding efficiency).
  • Substantially rework initial motion estimation (9% reduction in encoding time).
  • Optimise predictors for multipass motion estimation (0.3% to 0.4% improvement to coding efficiency).
  • Optimize chroma quantizer offsets for 4:4:4 sampling.
  • Merge new dav1d assembly code for x86.
  • Add high bit depth AVX2 assembly (9% to 31% reduction in encoding time for 10-bit video).
• Bug fixes:
  • Fix intra edge filter desyncs with 4:2:2 and 4:4:4 input.
  • Fix loop restoration filter with 4:2:2 and 4:4:4 input.
  • Avoid a buffer underflow condition in CDEF pad_into_tmp16().
  • Properly validate minimum RDO lookahead frames value.
• Changes:
  • Update speed presets:
    • Enable full SGR search for levels 0-4 instead of 0-8.
    • Enable fine directional prediction for all speed levels.
    • Enable reduced transform type search for levels 6-10 instead of 5-10.
    • Disable transform type RDO for inter frames.
  • Refactor CDEF to allow easier importation of dav1d CDEF assembly, as well as simplifying interaction between loop filters.
  • Remove leftover code ported from libaom.
  • Remove unused diamond motion estimation.

Full changelog here.

Transcoded H264 video to AV1 with FFmpeg and librav1e. Checked metadata in MediaInfo and tested playback in mpv and VLC.