When a client requests a bitrate above the GPU's HEVC/AV1 level ceiling, NVENC rejects
initialize_encoder. The old probe stepped the rate down by ×¾ each retry, undershooting
the real ceiling badly (a 1 Gbps request landed ~300 Mbps even with the level cap near
800). Replace it with a binary search over [floor, requested] that converges (±20 Mbps)
on the HIGHEST rate NVENC accepts and clamps to that — so the stream uses the full
codec-level bitrate. Factored the session open/config/init into try_open_session() for
the probe; split-encode rejection is disambiguated from a bitrate-cap rejection (retry
once with split disabled) and the floor fallback also tries split-disabled.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
enricobuehler
93a1444060