Phase 1 of codec negotiation, and the Linux software H.264 encode path it unblocks.
**Codec negotiation (core `quic`):**
- `Hello.video_codecs` (bitfield: CODEC_H264/HEVC/AV1) — the client advertises what it can
decode; appended as a trailing byte (older client → 0 = HEVC-only, back-compat).
- `Welcome.codec` — the single codec the host resolved and will emit; trailing byte (older
host → HEVC).
- `resolve_codec(client, host_capable)` picks the shared codec (precedence HEVC > AV1 > H.264)
or `None` → the host refuses honestly rather than sending an undecodable stream.
- Roundtrip + back-compat tests; cbindgen exports the CODEC_* constants.
**Software encoder (host):**
- The openh264 `OpenH264Encoder` (was Windows-only) is now built on Linux too — it's
platform-agnostic (consumes CPU RGB `CapturedFrame`s, statically-bundled openh264). `openh264`
moved to the shared linux+windows Cargo target.
- `PUNKTFUNK_ENCODER=software` selects it: `open_video` gains a `software` branch (H.264 only),
and `session_plan::resolve_encoder` / `capture::gpu_encode` resolve `EncoderBackend::Software`
→ `output_format().gpu = false`, so the portal capturer delivers CPU RGB. Explicit-only (auto
never picks it — a box with a dead driver still has /dev/nvidiactl and would mis-resolve NVENC).
**Host codec resolution (`punktfunk1`):**
- The native path no longer hardcodes HEVC: it resolves the codec from the client's advertised
set ∩ the host's capability (`Codec::host_wire_caps`: software→H.264, else HEVC), threads it
through `SessionPlan.codec`, and opens the encoder + validates reconfigures at that codec. A
software host + HEVC-only client is refused with a clear error.
- 4:4:4 is gated on HEVC (it's HEVC-only).
**Probe:** advertises H264|HEVC|AV1 and logs the resolved codec.
Validated on the GPU-less dev box: negotiation is live end-to-end (probe advertises 0x07 → host
resolves H.264 → Welcome reports it → plan = Software/H264), and the openh264 unit test (CPU RGB →
AnnexB IDR) now runs on Linux. Full capture→encode still needs a GPU on this box — every
compositor screencast path (KWin GL, gamescope VK_EXT_physical_device_drm, wlroots EGL) requires
one; software render (llvmpipe/pixman) can't be captured — so this box exercises negotiation +
encoder, not live capture. The software path unblocks GPU-less-*encode* boxes that still have a
display GPU. Phase 2 (clients advertising real codecs + decoding per Welcome.codec) is a follow-up.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
enricobuehler
ffc0b07b46