Videos are all playing now. My apologies for the outage.
Apparently on Saturday night we had an unprecedented CRASH of our Adobe streaming video server, and both the server and it's "watchdog" (the program that is supposed to restart it if it ever crashes) had both failed. The actual machine was still running, so I didn't get a crash alert.
This stuff always seems to happen on a weekend, unfortunately :-(
I am poring over the logs now to track down what could have been the cause...