v3.8.2

Automated release: version and notes generated from pull requests merged since 3.8.1.

Fixed

• --keep-alpha on an RGB source wrote BT.601 YUV with no colour tag (#496). A qtrle or
  PNG-in-.mov clip written to ProRes 4444 or VP9 by color.py --correct --keep-alpha,
  graphics.py --keep-alpha or overlay.py --keep-alpha held BT.601 samples and, on FFmpeg 6.1, no
  tag, so a player read a 1280x720 master as BT.709 and showed 30C050 as 26AB4D. --correct's RGB
  stage pinned bt601 on both legs, which cancel for a YUV source; an RGB source meets no matrix on
  the way in, so the way out was the one real conversion, and the alpha line converts nothing in
  front of it as the H.264 line does. Such a line is now BT.709 YUV and tagged BT.709 (--lut, whose
  samples already were BT.709, gets the tag; --lut-strength 0 gets the conversion), and RGB layers
  drawn on it are converted to match. Found by the sweep, the same conversion left to FFmpeg's
  BT.601 default: color.py --lut --keep-alpha --alpha-codec qtrle|png of an RGB source did not
  return the source's RGB under an identity LUT (30C050 written as 3CD753); color.py --keep-alpha --alpha-codec qtrle|png of a BT.709-tagged source read its graded YUV as BT.601 (the same
  3CD753); --alpha-mode premultiplied on a ProRes 4444/VP9 line of a BT.709 picture shifted
  opaque colour the same way; an RGB overlay.py --video layer on a BT.709 alpha line was BT.601
  (pure red read FF1800; with --chromakey it is keyed first, in the BT.601 the key is computed in). Commands for a YUV source are unchanged except in those three cases, each
  on a BT.709-tagged source. An untagged YUV source is unchanged everywhere, and
  an RGB source that probes HDR or BT.2020 is not converted to BT.709: FFmpeg's own conversion makes
  its YUV line, as before.
  The grade of an RGB source names no matrix on its way in to RGB (with one, FFmpeg 7.1 wrote
  BT.601 samples on the ProRes 4444/VP9 line).
• fix(color): an RGB source's YUV alpha line is BT.709 and tagged so (#498)

What's Changed

• fix(color): an RGB source's YUV alpha line is BT.709 and tagged so by @kajisho5 in #498

Full Changelog: v3.8.1...v3.8.2