Rated 4.9 (99 reviews)
Video Conversion: SDI, HDMI and Fibre, and Which Converter You Need
Why the picture drops out over long HDMI runs, what SDI does differently, and when the answer is fibre.
~8 min read · Updated August 2026 · By the Stage Supply team
In this guide:The three formats · Why HDMI fails · Converters · Embedded audio · Fibre · Picks · FAQ
Video at an event fails in a small number of predictable ways, and most of them are distance. HDMI was designed to connect a set-top box to a television across a living room, and it does that job well. Asked to cross a hall, it stops working, often intermittently, which is worse than failing outright.
This guide covers the three signal types you will meet, how far each one goes, and which box converts between them.
The three formats, and what they are for
| Format | Connector | Practical distance | Locks | Best for |
|---|---|---|---|---|
| HDMI | HDMI type A | Up to about 10 m, less at 4K | No | Source to nearby screen, laptops, consumer kit |
| SDI | BNC on coax | 100 m and beyond at 3G, less at 12G | Yes, twist lock | Everything on a stage or in a venue |
| Fibre | opticalCON or similar | Hundreds of metres to kilometres | Yes | Long runs, between buildings, electrically noisy sites |
SDI is the professional default because the connector locks, the cable is cheap and repairable, and it runs the length of a venue on a single coax. It also carries embedded audio, which HDMI does too but less predictably.
Why HDMI runs fail
Three reasons, and they compound.
- The signal is high bandwidth and the cable is not designed for distance. At 4K, ten metres is already ambitious.
- The connector does not lock. A cable that is fine at soundcheck is unplugged by a foot at the interval.
- The handshake. HDMI negotiates a connection between source and display, and every extra device in the chain is another negotiation that can fail. That is why a screen sometimes works and sometimes shows nothing at all, with no change in the cabling.
Converting to SDI at the source removes all three problems in one move, which is why the standard event answer is a small converter at the laptop and another at the screen.
Choosing a converter
Converters are simple boxes and the naming tells you the direction and the rate.
- **HDMI to SDI** at the source, so the long run is coax.
- **SDI to HDMI** at the destination, because most screens and projectors only accept HDMI.
- **Bidirectional** units do either, which is one part to stock rather than two.
- **Fibre converters** take SDI or HDMI onto optical, for very long runs or where electrical isolation matters.
The rate matters as much as the direction. 3G-SDI handles 1080p at normal frame rates. 12G-SDI is required for 4K at 60. Buy for the resolution and frame rate you actually need to carry, and check every device in the chain supports it, not just the ends.
The chain is only as fast as its slowest box
A 12G converter feeding a 3G router feeding a 12G screen gives you a 3G system with two expensive boxes in it. Rate support must be end to end.
Embedded audio, and where it goes missing
Both SDI and HDMI can carry audio inside the video signal. The catch is that converters vary in how they handle it: some embed and de-embed, some pass embedded audio through untouched, and some quietly discard it.
In practice this is where shows go wrong. If the sound from a video playback disappears somewhere between the laptop and the desk, the converter is the first thing to check. If audio matters, buy a converter that explicitly states it handles embedded audio, or take the audio separately on a balanced feed and keep it out of the video chain entirely.
When you need fibre
Fibre is worth the money in three situations: the run is longer than coax will reliably carry, the two ends are in different buildings or on different electrical supplies, or the environment is electrically hostile.
Because fibre carries no current, it also breaks any earth path between the two ends, which removes a whole class of interference problems. The connectors used at events are ruggedised, usually opticalCON, rather than the bare fibre connectors used in a data centre.
More on the underlying comparison in HDMI vs SDI for live events.
Popular picks from the shop
Theatrixx xVision HD Bidirectional Video Converter HDMI 1.2 / 3G-SDIView product →Theatrixx xVision HD Fibre to SDI Converter – MultiMode opticalCON DUO to 3G-SDIView product →Theatrixx xVision 4K Fibre to HDMI Converter – SingleMode opticalCON DUO to HDMI 2.0View product →Theatrixx xVision DUAL 4K Fibre to SDI Converter – MultiMode opticalCON DUO to 12G-SDIView product →
Frequently asked questions
How far can HDMI run?
About ten metres at 1080p with a good cable, and less at 4K. Beyond that use an extender or convert to SDI, which is the more reliable answer for an event.
What is the difference between 3G and 12G SDI?
Bandwidth. 3G-SDI carries 1080p comfortably. 12G-SDI is needed for 4K at 60 frames per second. The higher the rate, the shorter the usable cable run.
Will an SDI to HDMI converter carry the audio?
It depends on the converter. Some de-embed audio, some pass it, some drop it. Check the specification before buying if the audio matters.
Can I use satellite or CCTV coax for SDI?
It will often work over short distances, but the impedance and screening are not the same as proper SDI coax and the result is unreliable at longer runs and higher rates. Use cable specified for the rate you are carrying.
