pion no longer starts the repair stream reader when a custom BufferFactory
is set, so the mid/rid/rsid extensions were never observed and simulcast RTX
streams were never paired with their primary streams.
Extract the extensions on the buffer write path instead. Migrated publishers
send no extensions at all, so pair those from SimTracks.
Adds an integration test covering both paths, and moves the vnet setup it
shares with the downtrack test into pkg/testutils/vnettest.
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
* Resolve RTX pair via OnTrack also.
In simulcast probing path, the interceptor chain is not invoked
for primary stream. Not sure if this is a recent change. Due to this,
the RTX pair does not get resolved.
Use the onTrack callback to resolve the pair.
* remove debug
