This release focuses mainly on improvements to color space handling - including support for Dolby Vision Profile 5/8 content, completely rewritten HDR tone/gamut mapping, and bringing pl_color_space more in line with HDR10 metadata. Libplacebo now generally respects things like mastering color space metadata, especially for PL_INTENT_SATURATION.
Other notable changes include support for H.274 film grain synthesis, as well as improvements to the AVFrame<->libplacebo interop (in particular, support for hardware accelerated frames), and various fixes related to alpha transparency.
Full changelog here.