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punktfunk/crates
enricobuehlerandClaude Fable 5 9b7fc127ef feat(core): Automatic bitrate scales to measured link capacity — probe ceiling + slow start
The ABR ceiling was the negotiated start rate, so an 'Automatic' session
was permanently boxed at the 20 Mbps default no matter the link — the
most user-visible cap left after the transport work lifted the client
receive ceiling to ~4.8 Gbps wire.

- Startup link-capacity probe: ~2 s into an Automatic session the pump
  fires one speed-test burst (2 Gbps target, 800 ms) over the existing
  ProbeRequest machinery; delivered wire throughput x0.7 (FEC + variance
  headroom) becomes the controller's climb ceiling via set_ceiling().
  Old hosts decline (all-zero reply) or never answer (a 6 s timeout
  clears the stuck probe state so LossReports resume) — the ceiling then
  stays negotiated, exactly the old behavior. PUNKTFUNK_ABR_PROBE=0
  opts out.
- Slow start: until the first congestion signal, every cooled clean
  window DOUBLES the rate toward the ceiling (20 Mbps -> 640 Mbps in
  ~10 s) instead of +6% per ~10 s (which would have taken ~10 minutes).
  Any congestion signal ends it for good; classic AIMD takes over.
- Faster, severity-aware AIMD: a SEVERE window (unrecoverable frame,
  jump-to-live flush, or >=6% loss) backs off x0.7 immediately instead
  of waiting two windows; ordinary congestion (2-6% loss, OWD rise)
  keeps the two-window fuse. Additive climbs need 6 clean windows
  (~4.5 s, was ~10 s); the change cooldown drops 3 s -> 1.5 s.
- PUNKTFUNK_VBV_FRAMES now also scales the direct-NVENC VBV (Windows +
  Linux, previously hardwired to 1 frame) — parity with AMF/VAAPI/QSV.

Each accepted step still costs an encoder rebuild + IDR on the host;
in-place rate reconfigure (NvEncReconfigureEncoder / AMF dynamic
properties / Vulkan per-frame RC) is the planned follow-up that makes
stepping free. Controller tests rewritten to the new policy (severity
classes, slow-start climb, ceiling semantics; 144 green).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-07-14 19:28:11 +02:00
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