feat(camera): cap the H.264 transcode bitrate and make it optional - #39

Follow-up to #37 and #38. The H.265 path now works end to end — camera/capabilities returns ["hls","web_rtc"], Chrome on Linux plays smoothly and opens near-instantly, and the transcode is genuinely lazy (of three registered H.265 channels, only the open one has an ffmpeg process; the others sit at bytes_recv=0).

Inspecting the live go2rtc API with the camera open turned up a bad number.

The problem

Sampling bytes_recv on both producers of ch0 over 20 s:

Nine times the source. go2rtc's built-in h264 template (internal/ffmpeg/ffmpeg.go) is:

-c:v libx264 -g 50 -profile:v high -level:v 4.1 -preset:v superfast -tune:v zerolatency -pix_fmt:v yuv420p

No rate control at all, so x264 falls back to CRF 23 and spends bits preserving the compression artefacts the DVR already introduced. The observed WebRTC consumer was on a public IPv6 address — so that was 6.6 Mbit/s leaving over the internet to watch a camera whose source fits in under 1.

The fix

parseArgs supports #bitrate=, applied after the codec args:

if query["bitrate"] != nil {
    b := query["bitrate"][0]
    args.AddCodec("-b:v " + b + " -maxrate " + b + " -bufsize " + b)
}

The ffmpeg source becomes ffmpeg:<id>#video=h264#audio=opus#bitrate=<N>k.

Two per-device options, added to the existing options flow:

• Transcode H.265 to H.264 — toggle, default on. Off registers nothing with go2rtc and clears both repair advisories, since the trade-off was then made deliberately.
• H.264 transcode bitrate cap — slider, 256–8192 kbit/s in steps of 256, default 2048.

Resolution is deliberately left alone. Clients that decode HEVC keep receiving the original 2560×1440; the cap only affects the browser-facing path.

No new wiring was needed to apply changes: __init__.py already registers an update listener that reloads the entry, so the old entities tear down (unregistering the stream) and the new ones register with the new source string. _stream_has_sources keeps matching because the connected producer's URL carries the whole source string percent-encoded in ?source=, suffix included — verified against the live instance.

Testing

Measured before the change on the real device (0.73 → 6.60 Mbit/s, 9.0×). ruff, compileall, helpers/i18n.py --check and manifest key order all pass. Post-deploy checks to run:

1. Re-measure — the transcode should land near 2 Mbit/s instead of 6.6.
2. Only one ffmpeg, only for the open channel; the others still at bytes_recv=0.
3. VLC on rtsp://<ha>:18554/<identifier> still gets untouched H.265 2560×1440.
4. Move the slider, reopen: /api/streams should show the new #bitrate= in the producer source.
5. Untick the toggle: the xmeye_…_camera streams disappear, both repair notices clear, and HA recreates its own default stream on the next view. Ticking it back restores both producers.

🤖 Generated with Claude Code

https://claude.ai/code/session_011UpaDKeLbpQB7EapQBpKoJ