I wish that video had cooked a military-style ammo box filled with sporting ammunition. I wonder if the additional containment would yield an explosion.
Unless they all went off at once (not possible due to the outermost cartridges absorbing the heat first), the ammo can should easily contain all of the shrapnel. Would likely sound just like a busy popcorn machine. A bigger question is what will a container of powder do (for folks who reload, or shoot muzzleloaders). Those will make a pretty big boom.
Normal civilian cartridges should pose no harm to a firefighter in bunker gear. Bigger stuff like 50BMG does have more power, like a firecracker. There's a video of a 50BMG round in a microwave, it blew open the door, but didn't break the glass.
If you hear loose rounds cooking off, they won't hurt you... but certainly a warning to get out because there could be something bigger.