Screen mirroring

Reading time 3 minutes

Updated – October 13, 2023

Screen mirroring is a process for sending video and audio content from a cell phone or tablet via WLAN to a playback device, such as a smart TV or projector, and mirroring it there. to reproduce.

Most smart devices offer corresponding settings out of the box.

Connection establishment

The connection requires a shared WLAN and is initiated from the cell phone or tablet. By activating screen mirroring and selecting the respective output device on the mobile device, smart TVs or projectors display a usually four-digit number code that must be entered on the mobile device in order to establish the connection.

As soon as the connection is established, the content of the mobile device including audio is output to the playback device. This works for iOS and Android devices alike.

Screen content from desktop or laptop devices running OS X or Windows can also be displayed and mirrored on such smart TVs or projectors.

Application example

Suppose you have a video camera with a LAN and HDMI connection whose audio and video signals are to be played back on a large smart TV. The camera and TV are in different rooms, possibly even floors, around 60m away from each other.

There is now the option to use an HDMI cable. However, with 1080 video resolution, it can only cover a distance of 10m.
With an HDMI to LAN converter set, consisting of a transmitter with HDMI input and LAN output, as well as a receiver with LAN input and HDMI output, you can cover long distances, even up to 120m, via LAN cable , even more so by cascading such sets.
However, this is not an entirely economical undertaking, especially if the same WiFi is available in both rooms. Screen mirroring via the shared WLAN is an option here, without any further (installation and cost) effort.

projector

A distinction must be made between conventional projectors and SmartBeamers. The latter support the above-mentioned screen mirroring.

A mistake often occurs when it comes to the lumen specification, the brightness output of the projector. Lumens and ANSI lumens must be differentiated in terms of their meaning.

Lumen refers to the brightness of the light source, while ANSI lumen refers to the brightness on the projection surface. So ANSI lumens are crucial in projector technology.

The choice of projector depends on the lighting conditions, room size and distance to the projection surface. A projector with poor lighting technology will not be able to provide an image worth seeing in a room that is flooded with light and cannot be darkened. On the other hand, a high-performance projector in a smaller room with only one narrow window will illuminate the room with its image as bright as day and will also not contribute much to the enjoyment of the viewer. The projector's contrast ratio and the properties of the projection surface also play a key role in the final image experience.

Although the recommendation has already been narrowed down, it is still not sufficiently defined. Therefore, two devices are described here as examples:

Assuming that there is a 4 x 4 m room with two windows arranged on one side, with a projection surface at 90° from it, a projector with around 2,000 ANSI lumens, such as the one in the lower price segment, is sufficient ViewSonic X1-4K Smart Home Projector at 1,299 euros with 2,150 ANSI lumens and 3 million:1 contrast ratio!

However, if there is a meeting room of around 20 x 10 m, the position of the projector is around 10 m from the projection surface, window surfaces can be darkened to reduce light, and are arranged at 90° to the projection surface, you will need a projector with at least 4,000 ANSI lumens, such as this also at a very moderate price level Optoma 4k 400X currently around 1,599 euros in unit with the one that implements the smart capability EZCast Pro Dongle II currently 149 euros.

A higher priced all-in-one alternative with smart functionality, 5,000 ANSI lumens and a contrast ratio three times higher at 3 million:1 LG ProBeam DBU510P currently 3,094.62 euros.

Of course, as always, there are hardly any limits to price.

All of the aforementioned projectors work using DLP (Digital Light Processing) technology, which, thanks to the encapsulation of the lighting system, ensures longevity and freedom from maintenance.

Projection surface

No matter how perfect a projector may be, if the projection surface is not of adequate quality, the image result will still leave something to be desired.

In addition to pull-out or stand-up screens, coated, reflective, etc., preference should be given to permanently mounted projection surfaces. On the one hand, frequent rolling and unrolling avoids the formation of waves and wear on the surface, and on the other hand, a permanently mounted projection screen is always cleanly stretched and ready for use at any time.

There are different sizes depending on the viewing distance. The size tailored to the room is calculated as follows:

• Recommended diagonal – room depth / 2
• Recommended screen height (format 16:9) – diagonal / 18.86 x 9
• Recommended screen width (16:9 format) – diagonal / 18.86 x 16

The above formulas apply accordingly to the formats 16:10 and 4:3.

Based on the two room examples described above, for the room measuring 4 x 4 m this results in a diagonal of 4 / 2 = 2 m, for the meeting room this results in 20 / 2 = 10 m.

The screen height for the living room example is 2 / 18.86 x 9 = 0.95 m, for the meeting room 10 / 18.86 x 9 = 4.77, the width is 1.70 m or 8.48 m.

Now not all (meeting) rooms are as high as a cinema hall. That's why you're limited to the maximum room height minus the lower area, which is no longer visible from the rear rows of seats.

The largest possible projection surface for 4k resolution is the frame canvas of 400 x 225 x 2.7 cm can currently be implemented for 899.99 euros.