Iphone offline render of avasset track-- how to get packet size?

Does anybody know how to pull the max packet size from an AVAssetTrack? Or an AVAsset in general? I'm trying to set up an offline rendering audio queue by reading directly from the ipo开发者_运维技巧d assets, and I'm stuck trying to figure out how big to make my render buffer.

Thanks!

Will

Looks like you can't without examining all the packets first, so use some other criterion for picking the size.