What if we allowed people to specifc the duration in multiple different formats?

* number of seconds
* 5min10s (similar to what we used to have to specify video offsets, but that doesn't seem to work on pyvideo anymore)
* HH:MM:SS

This should be fairly easy to implement in the admin, we could even use a custom admin widget with some fancy JS (think datetime widgets for duration).

However, this doesn't really help when entering data through the API. I'm not sure that case is a big issue though, people using the API can easily convert the numbers I think.