How to Send a Backup Stream to DCAST from OBS, vMix and Larix

A backup stream protects your live event only if it is set up before the event and tested once. This guide walks you through it in OBS Studio, vMix and the Larix Broadcaster mobile app. The idea is always the same: a second encoder sends the same show to your stream's Backup URL, using the same stream key. When the primary feed stops, DCAST switches viewers to the backup; when the primary is stable again, DCAST switches back.

Everything here is for streams you send over RTMP.

Before you start: find the two addresses

Open your stream's settings and go to the Connection tab. You will need three values:

On the PRO and VIP plans, the Backup URL accepts a feed as soon as you send one — there is nothing to switch on. On FREE and STAR the backup address does not accept a feed.

Step 1: decide what your backup protects you from

A backup only protects you from failures it does not share with the primary. Choose the strongest setup you can:

1. Best: a second computer (or a hardware encoder) on a second internet connection — a different ISP, or a cellular hotspot.
2. Good: a second computer on the same internet line. It protects you from a crashed or frozen machine, not from the line going down.
3. Weak: a second output from the same computer on the same line. It protects you from very little, because the computer and the line are shared.

If the venue gives you one camera feed, an HDMI or SDI splitter can send the same picture to both machines. A phone running Larix on cellular data is a realistic last-resort backup when nothing else is available.

Step 2: match the settings on both encoders

The closer the two feeds are, the less viewers notice a switch. Use the same values on both:

The keyframe interval matters most. DCAST switches between feeds on a keyframe without re-encoding your picture, so a long keyframe interval makes the switch wait longer.

OBS Studio

OBS streams to one destination per instance, so the backup normally runs in a second copy of OBS on a second computer.

On the main computer:

1. Settings → Stream → Service: Custom.
2. Server: paste the Primary URL from DCAST.
3. Stream Key: paste your stream key.
4. Settings → Output: set Keyframe Interval to 2 s.

On the backup computer:

1. Build the same scene (or at least a scene with the same resolution and audio).
2. Settings → Stream → Service: Custom.
3. Server: paste the Backup URL from DCAST.
4. Stream Key: paste the same stream key.
5. Match the output settings from Step 2.

Only one computer available? You can run a second OBS instance with the --multi launch option, or use the third-party Multiple RTMP outputs plugin to add a second output pointed at the Backup URL. Both run on the same machine and the same internet line, so they protect you from an OBS crash and little else. Treat them as a stop-gap, not as a backup plan.

vMix

Option A — a second vMix (or OBS) machine. Configure it exactly like the OBS backup computer above: destination = Backup URL, the same stream key, the same quality.

Option B — a second destination on the same machine. In vMix's Stream Settings, add a second destination:

1. Destination: Custom RTMP Server.
2. URL: the Backup URL from DCAST.
3. Stream Key: the same key as destination 1.
4. Keep Use Stream 1 Quality ticked so both feeds are identical.

vMix documents several simultaneous streaming destinations (the exact number differs between its help pages). As with OBS, a second destination on the same machine and line is a weak backup; use it to protect against a single stream connection failing, and prefer Option A for events that matter.

Larix Broadcaster (iOS / Android)

Larix is ideal as a cellular backup: a phone on a tripod, on mobile data, pointed at the stage.

1. In Larix, open Settings → Connections → New connection.
2. URL: paste the Backup URL from DCAST, add a /, then paste your stream key at the end.
3. Mode: Video + audio.
4. Video settings: match the resolution and frame rate of your main encoder if the phone can sustain it; set the keyframe interval to 2 seconds.
5. Make sure only this connection is active, and start streaming.

If the phone is your primary and a computer is the backup, swap the addresses: the phone uses the Primary URL, the computer the Backup URL.

Step 3: start the backup before you press Start

Start both encoders first, and only then press Start in DCAST. When the backup is already connected at Start, the broadcast begins on the protected path, and a later failure costs your viewers only the fraction-of-a-second hitch of the switch.

If the backup connects while you are already live, it still works, but DCAST has to move the running broadcast onto the protected path first. Viewers see one brief hitch at that moment; after it, the backup works as usual. Starting the backup before Start avoids that hitch.

Step 4: rehearse the failover

Do this before every important event. It takes five minutes.

1. Start the primary encoder. Open your stream's watch page on another device.
2. Start the backup encoder.
3. Press Start in DCAST as you would for the event — after both encoders are connected.
4. Stop the primary encoder (or unplug its network cable). Watch the player: the stream should continue from the backup. A hitch of a fraction of a second at the moment of switching is normal.
5. Start the primary again. Once it has been stable for a few seconds, DCAST switches back.
6. Stop both, check your local recordings, and you are ready.

If you ever lose both feeds, the player shows black with silence and waits; the broadcast is not ended. Start either encoder and the picture returns.

Step 5: record locally

Keep a local recording on at least one encoder — in OBS, Start Recording alongside Start Streaming; in vMix, Record. That file is your master copy for editing and re-publishing, independent of any network.

Troubleshooting

The stream does not switch when I stop the primary. Check that the backup encoder is really streaming to the Backup URL (not the Primary URL twice) with the same stream key, and that your plan is PRO or VIP — on other plans the backup address does not accept a feed.

Viewers saw a hitch when the backup connected. The backup joined after you pressed Start, so DCAST moved the running broadcast onto the protected path once. Next time, start the backup before you press Start.

The switch is slow. Check the keyframe interval on both encoders. It should be 2 seconds.

Colours, framing or volume jump at the switch. The two feeds differ. Match resolution, frame rate, audio sample rate and levels.

My encoder refuses the connection. Check that the stream key has no extra spaces, and that the server field contains only the URL, not the key (except in Larix, where the key goes at the end of the URL).