pipewire: read what a video node says it can do - #257
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The context binds every node already and installs the node listener with the param callback left null, so nothing ever asked a camera what it supports and a consumer had to guess. Ask video nodes for SPA_PARAM_EnumFormat and keep the answers on node_info, where the snapshot carries them to callers for free. Each candidate holds the format, the extent of the sizes and framerates it offers, and its DRM modifiers; a property may be fixed or a choice and both are read, since a choice stores its values past its body rather than at the start of the pod. Two things the shape forces. The node id is not on the param event and the bound-node vector moves its elements, so the listener is given a stable per-node record instead of the context. And the daemon assigns the sequence rather than the caller, so a round is identified by what the request returns: a node that re-advertises supersedes the replies still in flight, which would otherwise land on top of the new list and read as the union of both. An empty list means "not answered yet", never "supports nothing": a reader has to fall back rather than refuse. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019QWYTEhFJonuUNTEmBfv7Q
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The shared PipeWire context binds every node already and installs the node
listener with the param callback left null, so nothing ever asked a camera what
it supports and a consumer had to guess its format, size and framerate.
Video nodes are now asked for
SPA_PARAM_EnumFormat, and the answers are kepton
node_infoso the snapshot carries them to callers for free. Each candidate(
video_format_caps) holds the format, the extent of the sizes and frameratesit offers, and its DRM modifiers. A property may be fixed or a choice and both
are read, since a choice stores its values past its body rather than at the
start of the pod.
Two things the shape forces:
elements, so the listener is given a stable per-node record rather than the
context;
identified by what the request returns — a node that re-advertises supersedes
the replies still in flight, which would otherwise land on top of the new list
and read as the union of both.
An empty list means "not answered yet", never "supports nothing": a reader has
to fall back rather than refuse.
Why now
ossia score's PipeWire input panel uses this to offer only what the picked node
actually advertises instead of the whole table (ossia/score#2269). That branch
cannot build against a libremidi without it, so this is the first link in the
chain — libossia's vendored pin follows, then score's.
Rebased onto master; builds clean.
🤖 Generated with Claude Code
https://claude.ai/code/session_019QWYTEhFJonuUNTEmBfv7Q