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>
* WIP commit
* deficient handling
* Add missing ProvisionalAllocatePrepare
* adjust state on track removal
* Increase test timeout
* - Add comments about cooperative routines
- Take down transition if available in cooperative scheme
- Use layer comparison when taking down transition. Because of when the
bitrate is measured, it is not always guaranteed bandwidthDelta is -ve
when moving down.
- Do not add track to stream allocator till bind.
* make comment better
* a bit more clear comments
* Use OnBind on subscribed track
