Microvideo - Überblick über Switching Technologien

Microvideo are a leading provider of emergency backup switching. Their switches are in use by some of the world’s leading broadcasters 24 hours a day 365 days a year.

There are four types of switching which are in common use: relay, electronic, clean and seamless.

Relay
The simplest and lowest cost 2 × 1 switching method. Often used in bypass applications, relay switching is an electromechanical device. Relay switches do not switch cleanly, they will cause picture jump even with co-timed signals.

Electronic
Electronic switches switch the primary input in accordance with SMPTE switching standards, i.e. in SDI they switch on the relevant line in the next frames VBI, they do not, however, account for timing of the backup feed. In the event that both signals are perfectly synchronised the changeover can be clean, but in the more likely event of mistimed signals, the changeover will disrupt the picture being transmitted.

Clean
Clean switches will, as per the electronic switches, provide a switch in accordance with SMPTE switching standards. ‘Clean switch’ add-ons provide some scope for timing adjustment to compensate for mistimed signals and can therefore provide a clean switch. ‘Clean switches’ (and indeed electronic switches) are only clean on a manual changeover and will not provide a clean changeover should the primary input fail.

Seamless switching
Seamless switching works exactly as a clean switch in manual mode, but on loss of video it switches on a number of parameters such as missing line flags (rather than field flags), there will be an inbuilt delay of, normally, 5 lines, to allow a 100% clean ‘forced’ changeover, although this is normally user adjustable.
In ASI there is a similar approach, however, ASI streams generated, even from the same source, on different encoders, will have fundamental differences in how the packets are constructed.