oikos/investigations/2026-06-03-moonlight-sunshine-wifi-jitter.md

2026-06-03 — Moonlight/Sunshine game streaming unstable over WiFi

Summary

ludo-mini runs Sunshine as the game-streaming server; mac-mini runs Moonlight as the client. Despite both machines being on the same physical subnet (192.168.178.0/24), streaming was unstable — stuttering, dropouts, and high latency. Root cause: mac-mini is connected only via WiFi, while ludo-mini is wired Ethernet (2.5 Gbps). WiFi throughput shows 1-second UDP dropouts and high jitter (28 ms stddev), which breaks real-time video streaming.

Timeline

Pre-existing state

• ludo-mini: wired Ethernet (eno1, 2.5 Gbps), 192.168.178.181/24
• mac-mini: WiFi (en1, 802.11ac, 234 Mbps Tx rate, 1 stream, -60 dBm RSSI), 192.168.178.99/24
• Both on the same subnet via a consumer router at 192.168.178.1
• Sunshine configured: bitrate=80 Mbps, encoder=amf (AMD GPU), fec_percentage=5, hevc_mode=2
• Moonlight configured: bitrate=57 Mbps, fps=60, localaddr=192.168.178.181 (correct)

2026-06-03 — investigation

Network tests (iperf3 between mac-mini ↔ ludo-mini):

• TCP throughput: 49–86 Mbps, average ~65 Mbps — highly variable
• UDP throughput: 1-second complete dropout during a 5-second test; 0% loss otherwise
• Ping: 4.7 ms avg, but 28 ms stddev, max 138 ms — WiFi-level jitter
• Netbird P2P connection also showed 7 ms latency over the tunnel (unnecessary given same-subnet direct connection)

Additional findings:

• mac-mini has a built-in Ethernet port (en0) but it is inactive — no cable connected
• mac-mini also has Thunderbolt Ethernet adapters (en5, en6, en7) all inactive
• ludo-mini's en0 shows speed 2500 (2.5 GbE)
• Netbird routes 192.168.8.0/24 via utun100, but 192.168.178.0/24 traffic stays on en1

Root cause

mac-mini is on WiFi. WiFi introduces:

1. Throughput variance — 49–86 Mbps TCP fluctuation
2. Dropouts — 1-second UDP blackouts from radio retransmissions
3. Jitter — 28 ms stddev with spikes to 138 ms

Moonlight/Sunshine streams real-time video over UDP. Any jitter spike or dropout causes visual stutter or frame drops. The 57 Mbps Moonlight bitrate was too aggressive for the WiFi link's consistency, even though the average throughput is ~65 Mbps.

Mitigations applied

mac-mini — Moonlight (via defaults write)

Setting	Before	After	Rationale
bitrate	57 Mbps	25 Mbps	Reduce to a level WiFi can sustain consistently
framepacing	off (0)	on (1)	Smooths frame timing over variable latency
fps	30	60	Restored to game-appropriate value

ludo-mini — Sunshine (via SSH)

Setting	Before	After	Rationale
bitrate	80 Mbps	40 Mbps	Match Moonlight's reduced bitrate ceiling
fec_percentage	5	2	Less forward-error-correction overhead over WiFi
packetsize	(default)	1024	Smaller packets = less WiFi retransmit cost

Sunshine restarted after changes; confirmed active.

Open questions

1. Ethernet wiring — mac-mini has an active en0 port. Plugging it into the same switch/router as ludo-mini would eliminate WiFi jitter entirely. This is the definitive fix.
2. WiFi alternatives — If wiring is impractical, a WiFi 6 (802.11ax) USB adapter or Thunderbolt-to-Ethernet adapter would help, but wired Ethernet is the only reliable solution for game streaming.
3. Netbird route — 192.168.8.0/24 is routed over Netbird utun100. If Moonlight ever falls back to that subnet (ludo-mini's 192.168.8.133 LAN IP), traffic tunnels unnecessarily. Moonlight correctly uses 192.168.178.181, so this is not currently an issue.

Changelog

2026-06-03 — Initial investigation and mitigations

• Diagnosed WiFi jitter as root cause of unstable Sunshine/Moonlight streaming
• Applied Moonlight bitrate reduction (57→25 Mbps), frame pacing, fps fix
• Applied Sunshine bitrate reduction (80→40 Mbps), fec_percentage (5→2), packetsize (1024)
• Documented findings and open questions