How does this condition work? The only thing I see being assigned to `current_ds` is `None`. I'm guessing this part here is incomplete. Please add TODO comments with a short description in parts of the code that aren't done yet, so we know that we can skip over them during review.

I think 15 MB is too late to be giving a warning. Try asking on IRC or the mailing list what others think is a good threshold. Personally, I would say once you go below 1 GB. Thanh (@zxiiro) and Andrew (@fosslc) have the most experience with recording conferences with Freeseer, so they'll be able to give some useful advice here.