As is usually the case, the truth is not so glorious. If you wish to make synchronous switches, fades and keys in digital video signals, then they must be timed. I will explore the truth of timing in the real video world, and point out areas of concern and real pit falls which have come to the fore as real people begin to deploy real digital video systems. It is true, and should be understood, that most production switchers have some amount of auto timing. That statement needs a more complete explanation.
Most production switchers have a small amount of synchronization on each input.
That is from about one half to a bit more than two lines of video for a timing window. Not all inputs are automatically timed. Sometimes the various key cut signals are not treated in this auto timing function, and sometimes the auxiliary inputs are also not auto timed. Routing switchers don't have this auto timing feature, and neither do any other types of devices except frame synchronizers. The real problem with the auto timing, is that it works very well until something goes wrong.