Interfaces and transfer links

We all handle digital streams or files made up of video and audio signals, photos and graphics, to name just a few common examples. We need to store them on media in order to retain them for playback, editing and processing, or for distribution. As a result, there is already a need for transfers between the traditional source, microphone and camera, or working memory and the physical storage medium, within the workstation on which the various manipulations mentioned above take place. What's more, the streams and files we need to manipulate are not always physically where we need them, and, to be more precise, are not necessarily on any kind of support within the same station; so there again arises the question of transferring these streams or files from one workstation to another, located in the same room, in the same building or sometimes hundreds or thousands of kilometers away. It is sometimes necessary to carry out these transfers in real time and on a sustained basis; this is the case in particular, and among other examples, for video file transfers in production and post-production operations, and above all for broadcasting.

Compression, or bit-rate reduction, applied to all stages of program development, certainly makes things easier by reducing file size and the bit-rate required for reading and recording, but on the other hand it leads to pressing demands for file transfer at several times the nominal speed (2 or 4 times) in order to reduce the duration of these operations, which in any case represent a waste of time that it is quite understandable to want to limit. Interfaces already proposed or in the process of being proposed by manufacturers or specialized workgroups are evolving, or will evolve in the future, particularly in terms of the flow rates offered. This evolution obviously applies in the direction of increasing these speeds. The numerical values given in this document are therefore highly relative.

As a result of the digitization of its signals, the professional audiovisual sector has seen the arrival of IT products in the equipment of almost all our studios, to such an extent that today, all exhibition stands feature PCs of all types. This marriage between image and sound technologies on the one hand, and those of computing on the other, has barely been consummated when we find ourselves in the presence of a third domain, that of telecommunications. Each brings its own habits, vocabulary and transfer interfaces. That's why, after a few definitions, we've chosen to classify them according to the original world of interfaces and links, that of video and audio, then that of computing...