AJA Io 4K Plus review

AJA Io 4K Plus is a desktop production I/O device for a Thunderbolt workstation. Its value is not just the words “4K” on the enclosure: the exact specification lists 4096×2160 and 3840×2160 input formats through 60p, including HDMI 2.0 and 12G/6G-SDI paths. This makes it a different assessment from the smaller Io X3, which is limited to 2K/HD/SD. It is still professional video hardware with application and connection requirements, not a simple console passthrough card.

4K capture depends on the selected input route

On the HDMI side, the v18 manual identifies an HDMI 2.0 input and supports 4K/UltraHD up to 60p. It also expressly states that HDCP-protected inputs are not supported. An unprotected camera, computer or other HDMI source is the relevant type of input; this product is not a way to record protected streaming video. The SDI side supports a range of signal classes, including 12G and 6G, plus lower-rate formats. The sheet lists the 4K/UltraHD modes and explains that host attributes and the chosen configuration affect high-frame-rate availability.

The four SDI BNC sockets are flexible but not four identical independent 4K lanes. AJA documents four HD/SD bidirectional paths, a 12G/6G single-link input and output arrangement, dual-link modes, and a four-link 3G input or output arrangement. Each assignment consumes connectors differently. The product page and Quick Start Guide are useful for setup, but do not convert the connector count into a promise that several maximum-rate sources can be recorded simultaneously.

Capture applications and the 4K/OBS distinction

AJA's unified desktop software includes Control Room, which the manufacturer describes for capture, playback and monitoring. That is the application used for this assessment's 4K60 operating plan. AJA also lists OBS Studio and publishes a model-specific OBS Quick Start Guide. The guide demonstrates Io 4K Plus workflows, including a 4K/UltraHD source setup, but a hardware format table alone does not prove that every OBS version can capture every listed format at its maximum rate. This review therefore matches OBS conservatively at 1080p60 and does not assign a 4K60 OBS mode.

The same caution applies to HDR. AJA documents VPID and HDMI metadata support, HDR formats and metadata capture. It also says HDR compatibility depends on the application. That evidence is not enough to treat all 4K60 input as a guaranteed 4K60 HDR recording mode in any software/host combination, so the finder does not use an HDR-capture claim for this model. Confirm the exact frame rate, signal, color format, application, storage and monitoring chain when HDR is a requirement.

Output and monitoring are separate from capture

Io 4K Plus has HDMI and SDI outputs, as well as a dedicated SDI monitor output that AJA describes as down-converting 4K to 2K and UltraHD to HD. It can be useful in a production timeline or ingest setup where a supported app routes video to a reference monitor. But the down-converted monitor connector should not be read as a 4K60 passthrough port, and this assessment does not promise a consumer gaming display path. Likewise, a 4K output specification is not automatically evidence of unprocessed source passthrough while recording.

The unit has two Thunderbolt 3 ports, one usable for daisy-chaining another Thunderbolt device. Later Thunderbolt versions are listed as compatible, but host bandwidth, cable, software and storage still matter. The shape of a USB-C port is not the same as Thunderbolt support. AJA's current product page and v18 manual list Windows, macOS and Linux software paths; its OBS guide specifically documents Windows and Intel/Apple-silicon Mac for Thunderbolt OBS workflows. Check current release notes for the exact computer and OS rather than assuming all applications support all operating systems equally.

Production connectivity and practical limits

Io 4K Plus carries up to 16 embedded audio channels over SDI and eight over HDMI. Analog audio can be configured for eight input channels, eight outputs, or a split, but the specification says the DB-25 breakout cable is not included. There is a headphone jack and a 4-pin XLR power input; AJA lists an AC adapter. The device weighs about 3.4 pounds and measures about 8.74 by 8.11 by 1.65 inches, so it is compact in a studio-rack sense but not bus-powered travel gear. AJA documents HDR signaling and metadata capture, reference/timecode and RS-422 features for production workflows; those do not remove the need to configure the correct signal and app.

This model is most relevant when an unencrypted HDMI 2.0 or compatible SDI source must be captured at a documented 4K/UltraHD mode, and the workstation has Thunderbolt and an application that supports the intended route. It is less compelling for a basic 1080p stream, for a system with only generic USB-C, or for a gaming workflow that needs a specified passthrough/HDR/VRR combination. Before ordering, confirm the input connector and cable, HDCP status, Thunderbolt capability, current AJA driver and Control Room version, storage throughput, chosen SDI link configuration, and the exact retailer package and return terms.

This is a source-based review, not a hands-on test. It makes no claim about measured performance, present availability, a seller's exact bundle, price or customer experience. The primary references are AJA's Io 4K Plus product page, its model specification sheet, the current v18 manual and AJA's OBS Quick Start Guide v17.1.