Review (critico) caught a regression: the prod agent image ships a BtbN GPL
ffmpeg with libplacebo COMPILED IN but no Vulkan runtime (debian-slim, no
libvulkan1/mesa-vulkan-drivers/nvidia ICD). The presence probe (ffmpeg
-filters) would flip HasLibplacebo on, the filter's Vulkan device creation
would fail at runtime, and HDR sources that previously tonemapped via zscale
would break.
- FFmpegSupportsLibplacebo now RUNS the filter on one synthetic frame and
requires a clean exit (forces Vulkan device init + filtergraph negotiation),
so it is honest about THIS host: works on Vulkan-capable hosts, falls back to
zscale where Vulkan is absent. Logs the real ffmpeg error on failure.
- Warm the libplacebo (Vulkan init ~1.7s) + zscale caches in a background
goroutine at startup so the first stream session doesn't pay the probe and
risk its setup timeout.
- Benchmark: margin 1.5x -> 2.0x (the probe measures encode only; real decode
of HEVC/10-bit + busier content needs more headroom), per-probe timeout
12s -> 6s + overall 45s -> 20s (it blocks registration on software hosts),
and a 'no rung measured' case (missing lavfi/wedged ffmpeg) now keeps the
1080 default instead of flooring at 480 — an infra failure isn't a slow host.
Verified e2e on the fixed binary: LOTR Two Towers (HEVC 3840x1608 10-bit
HDR10/PQ, 12GB) on desktop-Chrome caps -> hls, ffmpeg runs h264_nvenc with
-vf ...,libplacebo=...:format=yuv420p:tonemapping=bt.2390 (zscale chain
replaced), 45 fMP4 segments, ffprobe confirms output h264 yuv420p bt709
(tonemapped from bt2020/smpte2084), no ffmpeg errors.
Replace the guessed transcode ceiling (CPU->1080, GPU->2160) with a measured
one. HW encoders still return 2160 instantly. A software-only host runs a
bounded encode benchmark — 3s testsrc2 through the real libx264 superfast
settings at 1080/720/480, top-down — and reports the rung it sustains at
>=1.5x realtime (margin for real decode + busier content).
Fixes risk 2: a weak NAS/old CPU that is ffmpeg-capable but can't keep up
with a 1080p software encode no longer advertises a 1080 ceiling, so
decideStreamPlan routes oversized sources to an external player instead of a
stuttering transcode. Floors at 480; each probe is timeout-bounded so a
wedged ffmpeg can't stall daemon startup.
