Field test: mobile data, bonding and failover

Streaming over mobile networks can only be tested where coverage is good. This test needs no computer and no Wi-Fi. The phone streams to a test receiver (server/test-receiver) that logs every network path every 5 seconds and records the stream, and the app keeps its own per-second log of each stream. Both are analysed afterwards and matched by time.

What you need

• Streaming phone with a data SIM, running NexusIRL with the VPS bonding stream (srtla://…:5000?passphrase=…) selected.
• For bonding (tests C and D): a second phone with a data SIM, ideally on a different carrier (if one network fades, the other may not). It runs a Moblink relay (NexusIRL, or Moblin on an iPhone) and joins the streaming phone’s hotspot, so no Wi-Fi network is needed. Without a second SIM, do tests A and B.
• Batteries charged, ideally a power bank.
• Mobile data: about 37 MB per minute at 5 Mbps; the whole test uses roughly 0.5–1 GB in total, shared between the SIMs in tests C and D.
• Safety: the person holding the phone must not be the driver.

Before you leave home (once)

On the streaming phone:

1. Select the VPS bonding stream (Streams → tap its circle). Do not select a Twitch stream.
2. Main screen (scroll the controls down) → Moblink → Use other phones as relays: turn on and note the password.

On the relay phone (bonding only):

• Android: install NexusIRL. Main screen → Moblink → Moblink relay: turn on, enter the same password. Android Settings → Developer options → Mobile data always active: on. Without it, some phones drop mobile data once they join a Wi-Fi network (the hotspot).
• iPhone (Moblin): Settings → Moblink → Relay: turn on, same password; leave Streamer off. If it does not find the streaming phone, turn on Manual and enter the address the streaming phone’s Moblink page shows (ws://…:7777).

Only the streaming phone has “Use other phones as relays” on; only the relay phone has its relay on. With the roles the other way round, the relay never connects.

At the location

Pick a spot with good coverage (full bars, 4G or 5G). If you can, run a speed test on the streaming phone and note the upload speed; streaming needs at least about 3 Mbps up.

Write down the time at each step (a photo of a clock or a note on the phone is fine).

Test	Steps	What it shows
A. Mobile only, standing still (3 min)	Wi-Fi off on the streaming phone. Go live, wait 3 minutes, End stream.	The stream runs on one mobile network; how the bitrate settles.
B. Mobile only, moving (5 min, optional)	As A, while walking or as a passenger in a car or bus.	Adaptive bitrate through changing coverage and cell handovers.
C. Bonding (3 min)	Turn on the streaming phone’s hotspot. Connect the relay phone to it. On the streaming phone, the Moblink screen should list the relay. Go live, wait 3 minutes, End stream.	Both SIMs carry the stream.
D. Failover (4 min)	As C. After 1 minute turn on aeroplane mode on the relay phone; after another minute turn it off again. After 1 more minute, End stream.	Losing one network does not stop the stream, and the path comes back.
E. Camera taken away (2 min)	During any test: open the phone’s own Camera app for about 10 seconds, then go back to NexusIRL.	The stream keeps running with the last picture while the Camera app has the camera, and the live picture comes back by itself as soon as it is closed.
F. Heat (during the longest test)	Every 10 minutes, note the thermal state in the status line and the battery percentage.	Whether the phone gets hot enough to slow down at this bitrate.
G. Opus audio (3 min)	Streams → edit the VPS stream → Audio → Codec: Opus, Save. Go live as in A, End stream after 3 minutes. Set it back to AAC afterwards.	The server receives Opus audio, in sync with the video.
H. Recording while live (2 min)	During any test: tap Record, wait a minute, tap it again. Then End stream.	The stream keeps going while recording, the recording is saved (AAC audio even in test G), and it plays.
I. Car Bluetooth (any test, in a car)	Connect the phone to the car’s Bluetooth before going live.	The microphone in the status line stays Built-in: the car stays a speaker (“Bluetooth output only”).

During each test, watch the status line at the top of the controls: it should stay LIVE (red). Note the time of any “Reconnecting”. Under the bitrate, a line shows each network’s share of the data, for example “100% Cellular” in test A, or “55% Cellular, 45% Pixel” (the relay phone’s name) in tests C and D. In test D the relay’s share should drop to 0% and come back.

Checks at home (no drive needed)

New in v0.5.0, on the streaming phone unless noted:

1. Torch brightness (Android 15+): torch on, the slider next to it changes the brightness. On an older phone (Android 10) the slider is not shown and the torch works at full strength.
2. Stream key protection: Streams → edit a stream → Show on its URL asks for the fingerprint, face or screen lock; Cancel keeps it hidden. Going live never asks.
3. Paste stream key: copy a stream key, then Paste stream key or URL in the editor puts it in the URL.
4. OBS (OBS 28+ on a computer on the same Wi-Fi): OBS → Tools → WebSocket Server Settings → enable, set a password. In NexusIRL: Streams → edit → OBS remote control: on, ws://<computer's IP>:4455 and the password. The main screen shows “OBS: …”; the OBS quick button (turn it on under the quick buttons’ Edit if it is not shown) switches scenes. A wrong password shows “Authentication failed.”.
5. Twitch (weekends only, on your own channel): sign in to Twitch again in the stream’s settings to get the new alerts (hype trains, polls, predictions).

Afterwards (within 2 days)

1. On the streaming phone, tap Share diagnostics (bottom of the main screen) and email the file to yourself. It contains the per-second log of the last 10 streams, with keys and passwords removed. If you used a relay phone, do the same on it.
2. Send the diagnostics file(s), the times you noted and the speed test result.

The test receiver keeps recordings for 2 days, so send these within 2 days.

How it is analysed

• Phone stream log (in the diagnostics file): every second the frames sent, encoder, target bitrate, round-trip time, SRT retransmissions and each network path’s share and round-trip time, plus every state change (LIVE, Reconnecting and why) and the phone’s temperature status.
• Receiver log (journalctl -u nexusirl-srtla on the server): every 5 seconds each path the receiver sees (the phone’s public address on that network) with packets per second and Mbit/s.
• Recording (/var/lib/nexusirl/recordings, 10-minute segments): gaps and frame rate as a viewer would have seen them.

Both logs use the phone’s local time, so the three line up.