"At some point we will have all services for media and information use on a single device" - a vision of the future that seemed likely just a few years ago and was advocated by many experts in the industry. However, the development is contradictory: instead of fewer and fewer screens, we have more and more devices of various sizes and for a wide range of applications.

For content providers such as online video libraries, who strive for the highest possible market penetration, the complexity of conception, design and implementation of apps increases enormously. It is no longer enough to just launch an app, instead providers have to decide whether they want to launch applications for mobile and tablet (each for the different operating systems), browser, Windows 8 and for the different TV platforms such as smart TVs, STB, consoles and HbbTV.

Once the question of which platforms are operated in which order has been clarified, the challenge of how these differ from the user interface and the range of functions and content will soon be faced. It is important to keep the UX consistent between the platforms as well as to maintain the platform specific characteristics. Transferring the interaction behavior of a touch device 1:1 to a TV interface that can be operated with a remote control is therefore just as unsuccessful as breaking the "back" paradigm of a device within the app. In addition, there are limiting factors such as legal restrictions, device performance and requirements of OTT providers such as Apple TV that require a device specific adaptation of the application.

To ensure that users of a service feel equally at home on the various platforms, there should be connecting elements that facilitate orientation and standardize the experience, despite all restrictions and differences. The central question is therefore which elements of the user interfaces can fulfill this connecting function.

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The information architecture represents the skeleton or framework of the application and is ideally structured in such a way that the user journey is guided through a service up to the consumption of content. A consistent structure helps the user to maintain orientation across the platforms and to find relevant content quickly and easily. The information architecture is therefore an important connecting element between different platforms and should only be changed in exceptional cases.

The essential contents and functions of a service should also be equally accessible across all devices. For smaller screens or for devices with limited usability (e.g. TV), it can still make sense to outsource complicated functions and settings to e.g. the web.

Navigation paradigm and view types should be adapted to the respective device, as they are strongly influenced by the size of the screen and the way it is operated. For example, the distribution of elements on a view does not play a major role in the design of a touch or mouse interface, since the finger or mouse can move freely across the screen. In the case of TV interfaces that rely on a spatial focus, however, the placement of e.g. navigation and functions is quite a challenge because the elements must all be accessible with the focus within the shortest possible distances. As a result, the requirements for navigation and view types are very different and do not necessarily have to be standardized across platforms.

Of course, the design should ensure the recognition of a brand. Colors and shapes reflect the corporate identity and will therefore be found in all applications.

In practice, it boils down to weighing up the above-mentioned factors for each individual case and the resulting costs for implementation and operation. Nevertheless, it should be noted that applications are as similar as possible in terms of information structure as well as content and functions, reflect the brand and at the same time meet the special requirements of the device.