Frequently Asked Questions. 


Under what kind of license is it distributed?

There are basically two options here:

  1. The pure GPL/LGPL approach using your own hardware. This consists of a modified omxplayer for each slave and a standard ffmpeg (or avconv) for the master.

    1. A modified version of omxplayer (GPL) which is linked with two of our own libraries, libpwtilemap and libpwutil

    2. libpwtilemap and libpwutil are used for managing command-line arguments and calculating the geometry mapping of the video image.  These libraries are released as LGPL and are themselves linked to glib, which is also LGPL.

  2. A more integrated turnkey solution which will include our bespoke hardware rack system to contain multiple Raspberry Pi computers and extra display software. This is in the process of becoming a Kickstarter project. These Pi Racks contain up to six Raspberry Pi’s with associated power distribution, communication and monitoring enhancements, desktop mirroring software and tools to aid content management. Pi Racks can be chained together to form larger walls or multiple walls. The extra software contained in these turnkey solutions is not released under a GPL style licence.


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What displays are you using in your 9 screen demo video?

Iiyama ProLite E2481HS 24” monitors that have 11mm bezels and cost approx £150 + VAT


What kind of displays/screens can I use ?

Basically any computer monitor or domestic TV that supports either HDMI, DVI or composite video inputs. You can purchase HDMI to VGA and HDMI to component convertors that range in price from about £20 to £100.


Do the screens have to be identical ?

No, you can mix any compatible screens (see “What type of screens can i use?”) within a PiWall. This includes screens of different sizes, different aspect ratios (4:3 - old square TVs and 16:9 - widescreen), different resolutions and different orientations. See this video for some examples of mixing different screen types.


Do you compensate for bezels (the plastic surrounding the screens) ?

Yes, we can even compensate for bezels of different thickness for each screen. You can also turn bezel compensation off if you are displaying mostly text content that wasn’t created with a video wall in mind.


Can you cope with large gaps between the screens ?

Yes, think of the screens as windows onto a larger virtual screen behind. You can actually create some amazing effects with screens positioned with large gaps - very good for concert visual effects.

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Where is the software ?

See Create your own GPL movie PiWall for instructions and download links.


How do I install the GPL version of the software ?

Installation instructions are not written yet ;-) - maybe tomorrow!


Which operating system do you use ?

We use the standard Raspbian “Wheezy” release available at http://www.raspberrypi.org/downloads


How many Raspberry Pi computers will I need?

You will need 1 slave Raspberry Pi for each screen plus 1 extra to act as the master controller. So a 9 screen system as in the demo will require 10 Raspberry Pi Computers.


How many screens can a Pi Wall handle?

This is basically from 1 to as many as you can afford! There is no real limit to this except physical space and your budget.


Which video formats can you play on the Pi Wall?

We can play mpeg4 and h264 encoded movies. There are many tools to convert between formats, we recommend the free ffmpeg tools that are available for Windows and Linux and you may wish to try a  graphical front end if you aren’t happy with the command line.


Can I use a Pi Wall to mirror my desktop ?

Note, this software will only be available with the purchasable turnkey solution.

We have developed our own desktop mirroring software that works in conjunction with the GPL movie playing software. At present the server is only supported on a Raspberry Pi master but it is possible to run a standard VNCviewer on the master and use our desktop mirroring software to then broadcast the image to a PiWall.

The mirrored desktop is subject to the normal limitations of a standard VNCviewer, namely that it doesn’t cope well with graphically intensive operations so is not suitable for playing movies or graphically intensive games.


Can you display photos on a Pi Wall?

Yes, there two ways of achieving this

  1. Encode your photos into a movie and play it, for more details see this link.

  2. Use our desktop mirroring software - see above.


Can I play graphically intensive games on a Pi Wall ?

No, at present there isn’t a way of redirecting the output from games that use the GPU features directly.

What video inputs can a Pi Wall accept?

This is a tricky one, there are no HDMI, VGA, component or composite video inputs available but there are USB connections and a dedicated camera module input. We haven’t tested any USB video or camera devices but we have linked a Raspberry Pi camera module to the wall and used it as a giant virtual mirror. You can also use USB storage devices as a source of pre-recorded video files.

Can I have more than one Pi Wall displaying the same information ?

Yes, you can link as many PiWalls together as you like. Each PiWall can display a copy of the whole presentation or just a portion of the data on the other PiWalls, see this video of a six screen video wall linked to a nine screen video wall.

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When will it be available ?

The GPL/LGPL movie player is available now (8th September 2013).

The fully supported turnkey version, complete with a desktop mirror (VNC like) capability, management software, monitoring, control and “self healing” software will be available later in the year.

Is it Open Source ?

The movie player part of the software is available as open source, licensed under GPL and LGPL. Please see “Under what kind of license is it distributed” in the "Licensing" FAQ section for more details.


What is the video that you use for demonstrations ?

We use Big Buck Bunny  - partly because it is fully open source, but also because it is quite a demanding piece of video that acts as a reasonably good stress

test for the software and network, and The Future is Fusion because of our nuclear physics background.


Is there a delay between playing successive videos ?

This ultimately depends upon the software you use to control how videos are played but even using a simple shell script it is virtually undetectable by the human eye.

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