ATEM Signal Flow: A Worked Setup

How does signal flow through an ATEM switcher?

Everything you plan is deciding what plugs into each input and where each output lands. An ATEM is a production switcher: one job, three stages. Signal comes in on the switcher inputs (SDI, HDMI or both, depending on model). It gets switched and mixed internally on the program and preview buses through cuts, transitions and keys. Then it goes out on program, preview, multiview and aux.

Input and output counts, connectors and accepted formats differ across the ATEM range, so plan against the model in front of you rather than a generic picture of one: this is the general signal-flow method applied to one specific switcher.

Step 1, List every source and destination first

Do the counting on paper, before you touch a cable: list everything that feeds the switcher and everything the switcher feeds. Most oversubscribed-input surprises show up here. Weeks before show day.

• Sources in, each camera (main, wide, close, roaming), a playback machine, a presenter laptop for slides, a graphics or scoreboard feed
• Program destinations, the streaming encoder or built-in stream engine, the recorder or record media, the projector or LED processor for IMAG
• Monitoring, the operator multiview display, a director confidence monitor, a talent or stage monitor fed from an aux
• Audio in and out, mics and playback audio arriving at the switcher, program audio leaving on the stream and the record

Step 2, Check the sources actually fit the switcher

Before you draw a line, run a fit check: one subtraction that saves the most expensive load-in surprise.

Sources to switch (3 cameras + playback + graphics + slides): 6
Inputs available on an ATEM Mini Pro: 4
Spare inputs if you commit all sources: 4 minus 6 = -2
Negative, so this show does not fit an ATEM Mini Pro as drawn
An 8-input body (ATEM Mini Extreme, or SDI Extreme ISO for SDI cameras): 8 minus 6 = 2 spare, it fits

Step 3, Assign each source to a specific input

"Camera 2 into the switcher" is an intention. Camera 2 SDI OUT into ATEM SDI IN 3 is a fact a stranger can wire. This is the port-to-port step, where a plan becomes buildable. Assign every source to a numbered input. Record the connector and the format on the wire:

1. Put your primary camera on the first input and keep camera order sensible (Cam 1, 2, 3 adjacent) so operator muscle memory matches the multiview.
2. Land each source on a connector the input actually has: an SDI camera on an SDI input, an HDMI laptop on an HDMI input.
3. Where a source connector does not match, add the converter now (HDMI to SDI for a long camera run), and it goes on the gear list.
4. Note the video standard of each source (resolution and frame rate) beside it, you reconcile these in Step 6.
5. Reserve the spare inputs from your fit check and label them, so nobody assumes they are free signal.

Step 4, Route program, preview, multiview, and aux

The output side is where first-time ATEM diagrams go vague; each output type has a job and needs a named destination on the drawing:

• Program (PGM), the live line cut the audience sees. It feeds the stream encoder, the recorder and any IMAG projector or LED processor. Some models handle stream and record inside the switcher, confirm which is yours.
• Preview (PVW), the next shot the operator is lining up. It drives the operator's preview monitor and is not for air.
• Multiview, one output tiling all inputs plus program and preview into a grid, sent to the operator's display, their main window into the system.
• Aux, assignable outputs that carry any single source, or program, independently of the live cut. Use one for a clean stage feed, a talent monitor or a confidence display that must not show the multiview.

Draw each output to a real device with a real cable, exactly as you did the inputs. Program to encoder, program to recorder, multiview to monitor, aux to stage projector. Four outputs. Four rows in the cable schedule. If your model streams or records internally, note that so the crew knows there is no separate encoder to rig.

Step 5, Plan the audio path, not just the video

Audio is where switcher diagrams most often fall silent, literally. Audio reaches the ATEM's built-in mixer two ways. One is embedded in an SDI or HDMI input (camera audio, a laptop's HDMI audio). The other is dedicated audio inputs where the model provides them. Program audio is mixed inside and embedded back into the program output, so it rides along on your stream and record.

• Decide the source of your main program audio: a mic into the switcher, or an embedded feed from a camera or a house mixer feeding one input.
• Set each input's audio behavior deliberately, always on or audio-follows-video. A wireless handheld you want live regardless of shot is always on; camera ambience follows video.
• If a separate audio console runs the room, feed one mixed pair into the switcher rather than mixing every mic inside the ATEM.
• Confirm program audio is actually embedded on the output feeding your encoder and recorder: a silent stream is nearly always a routing miss, not a broken mic.

Step 6, Match one video standard across everything

One resolution, one frame rate: a switcher mixes sources that share a common video standard. Set the switcher to the standard you deliver in, then make every source match it. A source on a different frame rate is the classic reason an input shows black, tears or drops out.

1. Pick the delivery standard first (the resolution and frame rate your stream or record needs) and set the switcher to it.
2. Set every camera to the same standard, and set the playback and graphics machines to output it as well.
3. For any source that cannot match, put a scaler or converter in front of it, or rely on the switcher's input handling only if your model documents that it re-syncs inputs.
4. In multi-camera facilities, lock the cameras and switcher to a shared reference so they stay in step, see how genlock and reference work.

Verify the plan, then let it generate your documents

Verify a switcher plan like any signal flow: trace each path end to end and confirm every hop is real, once, before you call it done.

1. Does every source land on an input that exists on your model and is not already taken?
2. Is every format transition handled (HDMI to SDI, off-standard sources scaled or converted)?
3. Do record and stream survive if the projector or an aux dies? Where is the single point of failure?
4. Is every cable labeled with an ID and a signal name, so a stranger could rebuild the patch from the drawing alone?

Once the diagram is right, the documentation is nearly free. In WireFlow the same port-to-port drawing exports the gear list and cable schedule without retyping. Read-only links hand the plan to crew and client. For the field-ready workflow, see signal flow for crews. Then the broader broadcast signal-flow guides, and a full multicamera livestream signal flow for a deeper worked example.

Frequently asked questions

How many inputs does an ATEM Mini have?

ATEM Mini, Mini Pro and Mini Pro ISO carry 4 HDMI inputs; ATEM Mini Extreme and Extreme ISO carry 8; the SDI bodies mirror that split (4 SDI or 8 on SDI Extreme ISO), so confirm against the current Blackmagic Design datasheet before you quote gear, since the range changes.

Can an ATEM switch a mix of HDMI and SDI sources?

Connector types are model-specific: some ATEM bodies are HDMI-centric, others carry SDI, several offer both. What matters more than the connector is the video standard; every source has to share one resolution and frame rate. Confirm your model's connectors in the Blackmagic docs and convert where a source does not match.

What resolution and frame rate should I set the ATEM to?

Set it to the standard you deliver in (the resolution and frame rate your stream or record needs), then match every source to it: mismatched frame rates are the usual reason an input shows black or drops, and the standards a unit supports are listed in its Blackmagic datasheet.

Do I need a separate recorder and streaming encoder?

It depends on the model. Some ATEM units stream and record on their own; others expect an external encoder and recorder patched from a program output. Check yours, then draw whichever applies as an explicit destination so record and stream are planned rather than assumed.

Do all my cameras need to be genlocked to the ATEM?

Not always. Some ATEM models resynchronize inputs internally, relaxing the need for a shared reference on smaller shows; larger facilities still lock cameras and switcher to a common reference for solid sync. Confirm your model's reference behavior in the manufacturer docs, and see how genlock and reference work for the reasoning.

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