lgtv_audio_cap/docs/hyperhdr.md

Connecting to HyperHDR

HyperHDR's music effects read a local capture device. There is no network audio input to send to, no API to push samples into. Everything below is a way of working around that.

Three routes, in the order you should try them.

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1. RTP audio into a loopback device (recommended)

The TV sends RTP/L16 to the HyperHDR machine; a receiver there plays it into a loopback; HyperHDR captures the other end of that loopback. HyperHDR sees a perfectly ordinary sound card and does its own analysis, so every effect works exactly as it would with a real input.

TV ──RTP/L16 udp/5004──► lgtv-audiocap-receiver.py ──► hw:Loopback,0,0
                                                             ║ snd-aloop
                                        HyperHDR ◄──── hw:Loopback,1,0

On the HyperHDR machine

git clone <this repo> && cd lgtv-audio-cap
sudo ./host/install-loopback.sh --install-service

That loads snd-aloop (persisting it across reboots), keeps PulseAudio's hands off the loopback card, installs the receiver into /usr/local/bin and starts it as a systemd unit. It finishes by printing the exact device name to give HyperHDR.

To do it by hand instead:

sudo modprobe snd-aloop index=10 pcm_substreams=1 id=Loopback
./host/lgtv-audiocap-receiver.py --output aplay --device hw:Loopback,0,0

On the TV

Outputs → HyperHDR audio (RTP/L16)

Setting	Value
Receiver address	the HyperHDR machine's IP
UDP port	5004
Multicast	off
Announce over SAP	on (harmless, and needed for route 2)

Press Start.

In HyperHDR

Settings → Sound capture (in newer builds; older ones put it under the music effect itself) → input device hw:Loopback,1,0, then choose a music effect.

Checking it

# is anything arriving at all?
./host/lgtv-audiocap-receiver.py --port 5004 --output - | \
    aplay -f S16_LE -r 48000 -c 2 -

The receiver prints a line every 30 seconds with packet, loss and restart counts. Losses in the low hundreds over hours are normal on Wi-Fi; a steady stream of them means the TV's Wi-Fi is the bottleneck and the set really wants Ethernet.

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2. RTP straight into PulseAudio, nothing installed

If the HyperHDR machine runs PulseAudio or PipeWire and HyperHDR can reach it through the ALSA pulse device, you do not need the receiver at all. The TV announces the stream over SAP and PulseAudio builds a source from it.

pactl load-module module-rtp-recv sap_address=224.0.0.56

With Announce over SAP enabled on the TV, a source called something like rtp_recv.LG TV Audio Cap appears within five seconds. Point HyperHDR at its monitor.

This is the least code, but it is also the least predictable: PulseAudio's RTP receiver has no jitter buffer worth the name, and PipeWire's compatibility layer does not always implement the module. Treat it as a nice surprise if it works.

For unicast rather than SAP discovery, turn Announce over SAP off and load:

pactl load-module module-rtp-recv sap_address=0.0.0.0 port=5004

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3. The TV does the visualising

No host software, no sound device. The TV analyses the audio, renders a small image and sends it to HyperHDR's Flatbuffers port, the same way a hyperion-remote or a screen grabber would.

Outputs → HyperHDR visualiser

Setting	Value
HyperHDR address	the HyperHDR machine's IP
Flatbuffers port	19400
Style	Spectrum, Level bar or Pulse
Priority	150 (lower numbers win in HyperHDR)

In HyperHDR, make sure the Flatbuffers server is enabled (Settings → Network Services → Flatbuffers server, default port 19400).

What you give up: HyperHDR's own effects, colour calibration on the audio path, and any hope of the lights matching an effect you have configured elsewhere. The TV decides what the lights show. What you gain: it works in about a minute.

The three styles:

• Spectrum — 16 bands across the image, hue by frequency.
• Level bar — one bar that tracks the overall level.
• Pulse — the whole image flashes with the beat.

saturation and minBrightness shape the output; minBrightness: 0 lets the lights go fully dark between beats, which looks dramatic and slightly broken.

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Which one to use

	Route 1	Route 2	Route 3
Host software	receiver + loopback	none	none
HyperHDR effects	all of them	all of them	none, the TV renders
Latency	~100 ms	~100 ms, less stable	~40 ms
Robustness	good	depends on your PulseAudio	good
Setup time	10 minutes	2 minutes if it works	1 minute

Route 1 unless you have a reason.

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Latency

Roughly, end to end on route 1:

Stage	Typical
TV capture block	11 ms (512 frames at 48 kHz)
Network	1–5 ms wired, 5–40 ms Wi-Fi
Receiver prebuffer	60 ms, --prebuffer-ms
Playback buffer	80 ms, --latency-ms
HyperHDR's own analysis	20–50 ms

Around 150–200 ms in total, which for ambient lighting is imperceptible. If you want it tighter, lower --latency-ms and --prebuffer-ms until the audio starts crackling, then go back up one step.