First step of the W2 libav de-dup (plan §2.2, the missing Tier-2 mid-layer). The
three libavcodec backends (Linux NVENC, VAAPI, Windows AMF/QSV) each carried a
byte-identical pixel_to_av plus the SWS_POINT / SWS_CS_ITU709 (/SWS_CS_BT2020)
swscale consts. Hoist them into a new encode/libav.rs and import from super::libav.
The module is gated to compile exactly when a libav backend does (linux, or
windows+amf-qsv). Free fns/consts over borrowed handles — no per-frame dyn/alloc,
off the zero-copy path. Verified: Linux cargo check green (linux/mod.rs + vaapi.rs
compile against it); ffmpeg_win.rs is Windows-cfg — same mechanical swap, covered
by Windows CI on push.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
enricobuehler
3c38a5f0e8