The subject of playback solutions used in the live entertainment industry warrants a little booklet or at least a chapter of a book, but for the purpose of this website and as a brief introduction to the subject I hope this will do.

There are many types of playback solutions in use today and this little article's goal is to provide an introduction to this type of system component because no projection design can be realized without it.

Most of these products have not been conceived for the use in theater. However some have evolved over the years to cater to the theater community. The variety and number of options that is being offered these days is somewhat dizzying.

Of course initially it is important to understand why you need them in the first place. For the purpose of clarity this is the reason: The artwork, content or imagery needs to be send to a projector or screen in order to be seen by the audiennce. The part of the projection system which facilitates this aspect is the playback component. Usually media can be copied ot transfered to the playback system and once on the system it can be played back and send out via a cable to the projector or monitor. 

There are solutions which are realtively easy to use and quick to learn and products which require days of tutorials if not many weeks of practice. With demand for sophisticated control and features usually also comes an increased complexity to use or program these solutions. Therfore it helps to try a few different products over time to learn what they are capable of and how they address the needs of the projection designer differently.

There are stand-alone hardware solutions like Hard Drive players, flash memory players used for presentation Kiosks or the humble DVD player.
 A large variety of software has been re-utilized for the purpose of outputting to screens in the theater but was originally conceived for a different purpose, for example presentation software. Popular examples are powerpoint and keynote. 
Another example of repurposing software from another field of work would be VJ software. Popular examples are:

ArKaos Grand VJ
Resolume
Modul8
VDMX
COGE.


The available software keeps developing and changing so I have only listed the popular ones that are currently used based on what I know.
It is important to note that all the software mentioned relies on adequate hardware (Computer, hard drives, graphics card) to function. That is why they tend to have minimum hardware requirements. The software can only works as well as the hardware allows it to.
There are also programming environments that are completely customizable for the use in theatre. As the name suggests these require programming in a specific way that is particular to the software environment. I have also heard the term visual development platform in this context. They tend to be free or open source (with the exception of touch designer) and have a large community of users. 
Popular examples are:

Max/MSP

processing
quartz composer

touch designer

The fact that the hardware is crucial to the acceptable and predictable performance of the software is generally true and comes into focus when looking at the most popular type of software used in theater today, the so-called media server. 
Some manufactures offer their software only with propriety hardware (industrial grade rack PCs with high-end graphics cards as well as fast and resilient hard disk configurations). This way they can vouch for the performance and features of their product as well as support it in the knowledge what the customer actually has in front of them.

There are also software-only solutions which tend to be cheaper, but the user needs to take care to have adequate hardware to run these products on.
 As media servers have been designed with the live entertainment market in mind they offer a plethora of features and functions that go well beyond simple playback. 
All of them directly address multi-screen configurations of projectors, color effects, screen warping, simultaneous playback of multiple layers, compositing and on-system programming. 
Of course all this comes at a price as there is a lot of R&D involved.
 Significantly these products offer a variety of tools, not just a single tool. While a DVD player just reads a DVD and sends the resulting display data out via a port on its back, media servers can do a whole lot more. Thus I find it more apt to look at them more as tool boxes than just tools.
 Popular examples of software-only Media servers are:

Catalyst

MXWendler
Millumin
Watchout

Wings



Popular examples of media servers that are offered only on propriety hardware:

Arkaos stage server

D3

M-Box

Pandora's Box

Hippotizer

Most manufactueres of these media servers also offer software-only versions, but generally these can not be rented from an euipment supplier. I have focused on products that can generally be rented and thus are frequently used on professional productions.
Some popular software and hardware does not neatly fit into any of these categories:


Isadora - A node-based programming environment that was conceived as a live performance tool. It has a big community of users and is very versatile.

QLab - Originally a show control software designed to control and playback of sound and sound effects. Video capabilities were added with version 2 but are limited compared to a Media Server.
Raspberry Pi - A completely customizable and cheap micro computer.

While all the products above play back media not all offer a way to control or trigger playback from within the same product.
In other words some of these solutions will just sit there passively waiting for a trigger or signal that tells them to perform a specific action. Most media servers for example can be controlled with lighting consoles. However a computer than runs a powerpoint presentation may need a dedicated operator. Show control deserve careful and seperate consideration.

Lastly, I am not affiliated with any manufacturer or company. The reasons for writing this article are two-fold and causally connected: This information is not readily available anywhere and I do get asked about this subject more than I can remember. As far as the listed products go: The ones that I list are popular and in wide use as far as I know. If I have left anything important out please get in touch. The individual products can also be added and described in more detail in the key section. I am happy to expand on this article in time.