IMAG versus Streaming: LED Screens and Latency.

In a venue with a large screen, the audience looks at the screen before the stage. If the image arrives late relative to the sound, the effect breaks: people see the kick-drum hit half a second after hearing it. That mismatch is IMAG’s central problem and has nothing to do with the latency an internet broadcast can tolerate.

This guide separates two destinations that are often confused in a technical specification: venue screens, where the mismatch is immediately noticeable, and the streaming signal, where a delay of several seconds is perfectly normal. It also explains why each should receive a separate signal, the role of the clean feed and how to prevent unexpected content from reaching a giant screen.

What IMAG Is and Why It Differs from Broadcasting

IMAG stands for Image Magnification: the video signal shown on the venue’s own screens so the audience can see the action on stage up close. It is not a broadcast, although it may use the same camera chain and switcher. The difference lies in the destination and the time margin it allows.

Nothing prevents the same camera from serving both purposes. The treatment changes: IMAG cuts are designed for someone standing in front of the screen, using shots that work at that size without embellishment; streaming can accommodate faster cuts, captions and windows because it is watched on a small screen. If one director handles both, decide in the running order which shots are for the broadcast alone.

The spectator inside the venue hears live sound from the PA and sees the screen image. Their brain continuously compares the two, so any delay becomes noticeable. Someone watching the stream elsewhere has no direct reference to the venue’s sound, so a delay of several seconds does not bother them. That is why the two signals receive different treatment.

Acceptable Latency for Venue Screens

For IMAG, acceptable venue-screen latency is very low: in practice, the aim is to stay within one frame of the PA sound. At 50 fps, that is about 20 ms; at 60 fps, about 16 ms. Beyond two or three frames, the mismatch becomes visible, especially in close-ups of hands, percussion or fast movement.

Add every link in the chain: camera conversion, switcher processing, scaling, transport to the screen and the panel’s or projector’s own internal processing. Every conversion adds time, and scaling and format-conversion stages are usually the most expensive. Timing by hand with a stopwatch is ineffective; use a two-camera test or a flash within the shot.

IMAG, LED Screens and Latency

LED screens do not behave like a monitor. The signal enters a video processor, is distributed between modules and each panel refreshes at its own frequency. A properly configured LED panel can display an image with very little latency. If its processor applies scaling, double buffering or intermediate conversions, however, extra frames appear that are visible in IMAG.

Three settings determine almost everything: use the panel’s native resolution to avoid scaling, maintain the same frame rate as the rest of the chain to avoid repeated frames, and disable interpolation or image enhancement that adds buffering. Remember that LED screens emit their own light and their brightness competes with stage lighting: an overexposed panel will blow out in the camera image while the audience’s faces remain dark.

Projection versus LED Screens

Traditional projection onto fabric or another surface behaves differently. The projector usually adds more internal processing and the final image size depends on throw distance, so it is not always the fastest option. In exchange, it can cover irregular surfaces and work with unusual aspect ratios.

With projection, the distance from projector to surface requires calculation of throw and size. Changing the source resolution may require reframing the mapping, particularly noticeable in IMAG because the audience compares the screen image with the actual stage. Fix the configuration before setup and leave it alone during the show.

On a stage combining LED and projection, stage video and IMAG commonly share a destination. Decide what each screen does: LED for the live camera image and mapping for graphic content, or the reverse. Combining both on the same canvas multiplies conversions and, with them, visual delay.

Visual Delay: Measuring and Adjusting

Visual delay is the sum of every delay in the chain until the image appears on screen. You cannot eliminate it entirely, so the task is to reduce it and, where that is impossible, document it so nobody compares references that do not coincide.

To measure it, point a camera at a phone’s stopwatch and compare the screen image with the actual number; the delay can be read directly. If it is high, review the processing order: native resolution first, then frame rate and then any effect or layer. Unnecessary scaling or a poorly configured converter explains most cases. When the mismatch remains visible and cannot be reduced further, accept it and alert the team so it does not catch them out.

Different Signals for Streaming and Screens

Although they may come from the same switcher, streaming and venue screens need different signals. The broadcast includes mixed audio, graphics, captions and compression that adds seconds; venue screens need the cleanest image and the least processing possible.

A switcher auxiliary output solves this without duplicating cameras: programme with graphics goes to the encoder and a clean output goes to the LED processor. On a small system, reserve one AUX output for screens and another for the broadcast. The director can then add a live caption without displaying it at giant size inside the venue.

Watch the audio: the broadcast needs the master with music and voices, while the screen should carry no audio. Sending the broadcast mix to the video processor adds nothing and complicates the chain. Keep audio on its own path and limit screen video to the image.

Clean Feed for Production

A clean feed is the programme output without added layers: no lower thirds, logos or graphics and, depending on the situation, without certain windows. IMAG uses it because a giant screen amplifies every caption and composition error.

In practice, define a clean switcher output and label it accordingly. The screen operator works with that signal while the director builds the complete streaming programme without sacrificing anything. If you also record per-camera ISO, keep those signals clean for post-production too.

Protecting against Unexpected Content

A venue screen is a public medium in the most literal sense: nobody can know what will appear on it. Phone messages, supplier videos, open accounts or third-party material can reach the programme if the chain is not closed off. Protection against unexpected content relies on process rather than trust.

Whoever controls the source reaching the screen controls the risk. Separate the presentation laptop from the production laptop, keep sessions closed and check any external source before putting it on air. Tally and a preview output let you see what will be shown before sending it to the panel. Ask sponsors or external collaborators for files in advance and put them through the same review.

Next Step

With signals separated and delay under control, the logical next topic is broadcasting: Live Streaming: Encoding, Bitrate and Multistream covers codecs, bitrate, keyframes and multistream. If you need to review the complete chain first, return to Architecture of a Live Multicamera Production.