I almost caught it on video.

[Brad_bb]

I put a new band on today, and sawed one Ash log.  As I was going to edge one of the last outside boards, I noticed that the blade was oscillating relative to the outside guide. I inspected the band wheels to see if there was something on them causing this oscillation. Finding nothing, I slowly started engaging the band again right after this video and BAM!  The band broke. Clearly the oscillation was caused by a crack in the band that I did not see. Unfortunately the band bunched up inside the housing and partially cut my drive belt. So I'm down until I get another drive belt, which should be tomorrow morning. I had just changed my drive belt recently using my spare, and had not yet ordered replacements. At least now when I see an oscillating blade I'll know what to expect. I'll definitely stop and inspect the blade carefully.
Oscillating Band

[donbj]

That's a dead giveaway of a cracked blade. I can pretty much catch them before they break, either from what you see there or the sound it makes as it saws like that

[kelLOGg]

What donbj said. That is my experience, too.

[Tramp Bushler]

One of those learning curves.