webrtcsink's codec discovery builds its encoding chain with no output caps, so `force_profile` is
true and it inserts a capsfilter demanding `profile=constrained-baseline` — WebRTC's interoperable
floor. h264parse strips `alignment`, `stream-format` and `parsed` from a caps query but not
`profile`, so that demand reaches mpph264enc's src pad, whose template listed only
`{ baseline, main, high }`. Empty intersection, GstVideoEncoder's sink getcaps returns nothing,
and the failure surfaces upstream as videorate reporting it "could not transform NV12 ... in
anything we support". Discovery then drops H.264 with a warning nobody was reading, VP8 wins by
default, and the session dies in rtpvp8pay.
The element could always produce constrained-baseline; only its static template denied it.
Measured on an RK3566: `mpph264enc profile=baseline ! h264parse` negotiates
`profile=(string)constrained-baseline` on the parser's src pad, because baseline mode turns CABAC
and 8x8 transform off and MPP emits no FMO, ASO or redundant slices. So this widens the template
by one word rather than claiming something new.
Patches now live in a directory per upstream, applied by an `apply_patches` helper and recorded in
the MANIFEST as `patch <project>/<file>`. Two reasons: a patch aimed at the wrong tree failed the
same way a stale one does, and the MANIFEST's flat `patch <file>` line landed next to whichever
.so happened to precede it, which read as provenance for the wrong plugin.
Assisted-by: Claude:claude-opus-5[1m]
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