[Rust-KVM]

Requested by 4c

Summary

Before: the encoder always sent H.264 High profile, even when the browser negotiated Constrained Baseline. Linux Chrome offers no High entry, so its session negotiated 42e01f and then got a High 5.2 stream. Lenient decoders cope with that, but a strict decoder such as OpenH264 cannot decode CABAC and would show a black screen.

After: the encoder sends the profile that was negotiated. Browsers that offer High (Chrome or Safari on macOS, for example) still get High; baseline-only browsers get Constrained Baseline (SPS 42 c0).

How

When a viewer's ICE connects, negotiated_h264_profile reads the sender's negotiated codecs and picks the same codec that webrtc-rs binds the track to (the first exact match for 640034, otherwise the first H.264 codec). video::set_h264_profile then switches mpph264enc's profile property at runtime. The switch happens before the new viewer's keyframe is requested, so its first IDR already carries the new SPS. The choice is also applied on every pipeline rebuild, so supervisor restarts keep it. The encoder probe logs the SPS profile_idc whenever it changes, which makes the switch visible in the device log.

The level is still 5.2 while browsers advertise level 3.1 (1f). Every browser accepts that for 4K WebRTC, so this change leaves the level alone.

Testing

• cargo +nightly fmt --all
• cargo +nightly clippy -p rustkvm --release --all-targets -- -D warnings
• cargo +nightly test --workspace: this host has no GStreamer, so I cross-built the new h264_profile test and ran it on the device instead (6/6 passed). CI runs the full suite.
• Frontend touched: not applicable
• Tested on an RK3588 device at 3840x2160@60 with view-only headless Chrome (no HID input sent):
  • Log: H.264 encoder profile set to match the viewer, profile: "baseline", then encoder SPS profile, profile_idc: 66, with the IDR delivered 26 ms after the request.
  • The device encoded 59.8 fps with this change and 61.8 fps on the unmodified dev build. Both readings are 60 fps within sampling noise.
  • Bitrate on a static desktop was 3.7 Mbps with Baseline versus 3.4 Mbps with High, about 9% higher.
  • mpph264enc profile=baseline|main|high produces SPS bytes 42 c0, 4d 40 and 64 10 on this device.

Checklist

• No #[allow(...)] suppressions and no new unwrap() / expect() in production paths
• Hot paths stay zero-copy; periodic loops use MissedTickBehavior::Delay
• Shared protocol types live in rkvm-proto
• RPC method set changed → app/tests/rpc_methods.txt updated (unchanged)
• Module tree or build invariants changed → AGENTS.md updated (unchanged)

🤖 Generated with Claude Code