Video · Practical guide

DeckLink Duo 2: four SDI captures and ISO files in vMix

Two cameras appear in vMix while two others fail, even though all connect to the same Duo 2. Check the mapping between logical device and connector before changing every camera’s format. Then verify the signal received by each input and what the files contain: four filenames do not guarantee four different camera angles.

DeckLink Duo 2: inputs 3 and 4 and profile selection

Record Windows, CPU, GPU, vMix version, Desktop Video version and camera models. Check the received format at each input before comparing performance.

The official DeckLink Duo 2 product specifications describe four 3G-SDI connections configurable as input or output, supporting SD/HD up to 1080p60. Confirm the full name: Duo, Duo 2, Duo 2 Mini and Quad 2 are different models. Current documentation does not establish which driver was installed in the 2021 case.

Map subdevices and BNC connectors for the Duo 2 profile

The March 2026 SDK, section 2.4.11, pages 31–32 shows the Duo 2’s two profiles. bmdProfileTwoSubDevicesHalfDuplex applies to subdevice groups that share connectors; with both groups in that profile, the card provides the four paths shown in the diagram. Do not read the name as meaning only two channels for the whole card.

The table uses zero-based SDK indices. vMix may show different names: record the displayed name, card and physical port. Do not infer the BNC by counting down the list or copy the map from a Quad 2.

The bmdProfileOneSubDeviceFullDuplex profile pairs SDI 1/2 or SDI 3/4 and makes the other subdevice in each group inactive. Changing a profile affects its pair and may change supported modes. The page 33 warns that the driver may stop streams if an application does not handle the change. Save initial settings and make changes off air.

In Desktop Video Setup, open each Duo 2 device and record its assigned connectors. To test four independent captures, compare each assignment with the diagram and installed version. Recheck every affected device after changing one; disappearance of an error message is not enough.

Map subdevices and BNC connectors for the Duo 2 profile
SDK index	Group half-duplex profile	Group full-duplex profile
0	SDI 1	SDI 1 in/key and SDI 2 out/fill.
1	SDI 3	SDI 3 in/key and SDI 4 out/fill.
2	SDI 2	Inactive when its group uses full-duplex.
3	SDI 4	Inactive when its group uses full-duplex.

Test one signal per input before planning recording

We suggest using one recognizable camera or test source with a documented format and cable. Connect it to the identified port, select the corresponding application device and record image, audio and the full error, if any. Repeat by port while keeping the source fixed. Then connect event sources one by one and record resolution, p/i/PsF scan and exact rate.

If a combination fails, preserve the working record before comparing another cable or format. If inputs work separately but fail together, note which input or output was added and what changed elsewhere. Individual testing helps isolate a change; simultaneous load still needs testing.

The official vMix input/output note, updated October 3, 2016 lists four Duo 2 channels: for example, four inputs or three inputs and one output. It does not offer four captures plus four outputs on that card. Map External Output and any other application using devices; this does not establish a conflict on your system.

Use a different recognizable view for each camera in the test: a mark or framing helps reveal a duplicated source. Do not approve four ISO recordings based on four copies of Program. For the older Television Studio HD, see the return and auxiliary guide: its output number does not identify an isolated camera.

Two computers require a documented signal distribution path

The Duo 2 full-duplex profile documents input and output connectors; the diagram does not promise a direct camera pass-through between them. Available capture and playback paths do not verify an autonomous route or what happens when the application closes.

To plan two recorders, draw one branch per camera toward each capture device and mark where the signal splits. If a distributor, router or converter with loop-through is proposed, defer selection until its model, supported formats and behavior on power loss have been checked.

Test startup and shutdown of each recorder separately while observing the other. Record signal loss, recovery and sample files from both.

Check what each MultiCorder file contains

The vMix 29 MultiCorder help lists it for 4K, Pro and Max editions. Capture inputs are recorded without vMix effects or corrections; Output 1–4 retains processing. Choose the source required for delivery. Instant Replay and MultiCorder cannot run simultaneously.

For SDI cameras, Audio can select Input or a bus such as Master. Record that choice per file: camera audio and the program mix may serve different requests. Recording capacity depends on the computer and storage. The help calls for SSDs but does not validate a camera count for your system.

Prepare a take containing the cuts, clips and main recording planned for the event. Close the files and open each one: check camera identity, content, sound, duration and continuity. If a source is missing or an angle repeats, return to the capture map before changing the codec. Keep samples for review with the editor.

Complete the blank Duo 2 and ISO files worksheet. For more recording and delivery controls, see the event recording guide and multicamera plan.

Check what each MultiCorder file contains
Test record	Data to connect	Remaining check
Source and cable	Camera, transmitted format and card BNC.	Recognizable image and received audio.
Logical device	Application name, SDK index if available, and profile.	One input per source, without duplicates.
ISO file	Selected source, audio, filename and folder.	Open each file and check its content.
Simultaneous load	Main recording, ISOs and other planned tasks.	Continuity, samples and recovery by destination.

Share the map with operators and the file recipient

To review video processing and distribution with GLMedia, send the card model, Desktop Video version, application and format for each camera. Add ports, profiles and the audio requirement for each file. Mark what was observed and what still needs testing.

The DeckLink 8K Pro and profiles guide covers a different card and output synchronization. Keep each model’s scope distinct. Capturing four sources and approving a complete ISO recording are separate checks that must be documented.

Frequently asked questions

Does “Format Is Not Supported” on inputs 3 and 4 prove the cameras use another format?

The message alone cannot establish the cause. Save each input’s format, profile, device and error before comparing one variable on your system.

Does the Duo 2’s second logical device correspond to SDI 2?

In the diagram’s half-duplex profile, the SDK maps index 1 to SDI 3 and index 2 to SDI 2. Match these indices with the actual names in your application and the active profile rather than assuming the list starts in the same order.

Why does a device disappear when two connectors are paired?

In the Duo 2 full-duplex profile, SDI 1/2 or SDI 3/4 are paired and the other subdevice in that group is inactive. Check the profile and preserve its previous state. A change can affect the pair or stop streams; test it off air.

Can one Duo 2 capture four cameras and send four distinct outputs?

The model specifications and vMix note describe four configurable connections/channels, not eight independent paths. If outputs are needed, count the captures and playbacks required together and check the profile and selected hardware before planning the setup.

Does full-duplex turn the Duo 2 into an SDI distributor without software?

The diagram assigns input and output connectors, but does not document that autonomous path. Draw the distribution and verify the model that splits each source, including what happens when power is lost and restored.

Do four recorded files confirm four different camera ISOs?

Open every file and compare its source with the capture map. Look for repeated angles, listen to audio and check duration and continuity. Four Program files may contain the same mix; the count does not prove independent camera recordings.

Are vMix corrections included in camera-input ISOs?

MultiCorder in vMix 29 preserves an input without those effects; Output 1–4 includes processing. Record which one was chosen and check a sample with the editor before approving delivery.

Does an input ISO necessarily carry program audio?

Check Audio in MultiCorder: Input takes embedded source audio; a bus such as Master uses a different mix. Record the choice and listen to speech and clips in every test file.