Remote stream acknowledgments

This note describes current source builds. It does not announce a published release.

For an active capture.stream.start session, the viewer sends capture.stream.ack {streamId, seq} on the connection that started the stream. Each acknowledgment covers all frames through seq. Send an acknowledgment when each frame arrives.

Linux hosts allow max(4, ceil(fps × 0.2)) frames to remain unacknowledged: six at 30 fps and twelve at 60 fps. This capacity lets a 60 fps stream continue when acknowledgment round trips exceed the 67 ms ceiling of a four-frame window. The pending queue remains bounded by 200 ms of age, 200 ms of frames, and 4 MiB. These are queue limits, not a guarantee of end-to-end latency.

Mac hosts retain a four-frame window and pause input to the encoder at that limit. Both hosts end the stream after roughly three seconds without acknowledgment progress while frames remain outstanding.