The choice between SDI and NDI® comes up in almost every video production project: a new studio, an equipped conference room, sports capture, a training studio. The question is rarely “which one is best?” but “which one fits my constraint?”. Both transport professional video reliably. They do so according to two opposite logics, and it is that logic, not any absolute superiority, that should drive the decision.
SDI: the dedicated, point-to-point cable
SDI (Serial Digital Interface) is a family of SMPTE standards that carries uncompressed video over coaxial cable: for example ST 292 for 1.5G-SDI (HD) and ST 2082 for 12G-SDI (UHD). One source, one destination, one cable. To link a camera to a switcher, you run a cable; to add a destination, you add a distribution amplifier and another cable.
That physical simplicity is its greatest strength. The signal is uncompressed, transport latency is near-zero and deterministic, and behaviour is predictable: as long as the cable is within limits, the signal gets through, with no network configuration or software negotiation.
Distance does need nuance: the usable coaxial length depends heavily on the data rate (a cable perfectly viable at 1.5G-SDI may fall out of spec at 12G-SDI), on the cable type and on the connectors. For long distances, SDI can also be carried over fibre. That robustness keeps SDI the reference in environments where deterministic reliability comes first: heavy broadcast control rooms, OB vans, critical sports productions.
NDI: video as a network stream
NDI (Network Device Interface, developed by NewTek, now Vizrt) turns video, audio and metadata into IP streams that travel over an Ethernet infrastructure. A single network cable can carry several simultaneous streams, in both directions, plus control, tally, PTZ, and even power if the device is PoE.
The consequences are structural:
- Source discovery: NDI sources announce themselves on the network (mDNS); where multicast is not possible or desirable, a Discovery Server takes over.
- Bidirectionality: a single device can be both source and destination. A control room receives cameras and sends back a return feed or tally over the same cable.
- Software-defined expansion: adding a camera or an output becomes a matter of network capacity, not cable runs.
The key point, often misunderstood: “Ethernet network” does not mean “any network”. NDI requires a properly sized IP network, ideally dedicated or segmented for video (AV VLAN), with available bandwidth and a controlled configuration. The NDI documentation recommends a dedicated, high-bandwidth, high-availability network rather than one shared with office traffic.
For the protocol basics, see the Understanding NDI guide.
Full NDI, NDI HX, NDI HX3: what “NDI” really covers
NDI is not a single codec. Depending on the format, it relies on very different compression schemes, with trade-offs that radically change sizing and latency:
- NDI High Bandwidth (“Full NDI”): SpeedHQ codec, intra-frame compression (each frame compressed independently). Visually lossless quality, very low latency. In return, a high bitrate: on the order of 130 to 150 Mbps per stream at 1080p60, more in UHD.
- NDI HX / HX2: H.264/H.265 with a long GOP. Very bandwidth-efficient (a few Mbps), but encode/decode latency is higher (often 100 to 300 ms), so it should be avoided for live switching, monitoring or lip-sync.
- NDI HX3: H.264/H.265 with a very short GOP. A good compromise: on the order of 50 to 62 Mbps at 1080p60 depending on H.264/H.265 (lower bitrates possible depending on resolution, frame rate and settings), very low latency (on average under 100 ms depending on implementation), suitable for switching and camera control.
Practical consequence: saying “we use NDI” is not enough. The chosen variant drives bitrate, latency and therefore network architecture.
Sizing the network (the real critical point)
The common mistake is to reduce NDI to “you need a managed Gigabit switch”. The decisive factor is the total bandwidth budget:
- Count the number of simultaneous streams per port and per uplink. As a guide, a Gigabit link absorbs roughly 5 to 6 Full NDI HD streams at a reasonable load. Beyond that (multi-camera, 4K, recorders, monitoring, return feeds), you need a 10 GbE backbone and uplinks and a non-blocking network.
- Plan for segmentation (AV VLAN), PoE for PTZ cameras, and a discovery strategy (Discovery Server) on larger installations.
For multi-site, NDI is first very comfortable on a LAN or campus. Extending to the WAN is not automatic: it requires a dedicated architecture (NDI Bridge, VPN/private network, guaranteed bandwidth and controlled latency), or a complementary transport depending on the case.
Point-by-point comparison
| Criterion | SDI | NDI |
|---|---|---|
| Transport | Baseband signal on a dedicated link | IP stream on an Ethernet network |
| Compression | Uncompressed | By format: SpeedHQ (Full NDI), H.264/H.265 (HX/HX3) |
| Latency | Very low and deterministic (excluding device processing) | Full NDI: very low; HX3: low (under ~100 ms); HX/HX2: more variable |
| Quality | Highly predictable, no transport compression | Very good to visually lossless depending on format and bitrate |
| Scalability | Physical: cables, matrices, distribution | Logical: bounded by ports, uplinks, bandwidth, architecture |
| Distance | Limited on coax by data rate; extensible over fibre | Very flexible on LAN/campus; WAN possible with a dedicated architecture |
| Prerequisites | No network | A sized IP network, often dedicated/segmented |
| Complexity | Simple in a small setup, heavier at scale | Simple at first, demands real network skills as it grows |
What about SMPTE ST 2110? In high-end broadcast IP environments, the SMPTE ST 2110 family of standards (including ST 2110-20 for uncompressed active video) is another approach, more standardised and deterministic than NDI, but also more complex and costly to deploy. This article deliberately focuses on the practical SDI / NDI choice for AV, corporate, light live and hybrid production installations.
Do you really have to choose?
In practice, the “NDI or SDI” question is increasingly the wrong one. The two coexist in most modern installations. A camera can output SDI to a local recorder and NDI to the rest of the production; converters bridge both directions. Many professional cameras, including those from the brands HoriCast represents, natively offer both outputs (and, on the NDI side, both Full NDI and NDI HX) precisely to avoid forcing a choice.
The real decision concerns the backbone of the installation:
- SDI as the backbone suits cases where deterministic reliability comes first, the scope is fixed and the number of links is controlled: established broadcast control rooms, high-stakes sports productions.
- NDI as the backbone wins where flexibility, multi-room setups, remote operators or future growth matter more: web TV studios, conference rooms, campuses, houses of worship, training studios. Provided the network has been designed accordingly.
How to decide by context
The right reflex is to start from the use case, not the technology:
- Broadcast and post-production: SDI at the core of the control room, NDI for flexible contribution. See Broadcast Solutions.
- Corporate and meeting rooms: NDI leverages the corporate network, provided it is segmented. See Corporate Solutions.
- Sport and live: SDI for critical links, NDI for deployment comfort. See Sport Solutions.
- Education and e-learning: NDI to connect several rooms without dedicated video cabling. See Education Solutions.
In short
SDI and NDI are not competitors but complements. SDI offers physical simplicity and deterministic reliability; NDI offers scalability and flexibility that coaxial cable cannot, at the cost of real network design work and a variant choice (Full NDI, HX, HX3) matched to the target latency and bitrate. The choice of backbone depends on context, scope and the installation’s trajectory, not on a universal ranking.
To identify the right configuration for a project and the matching equipment, see the Where to Buy page to find a reseller, or get in touch for a technical discussion.