lmackreath wrote:but doesnt the inclusion of the advance xml allow you to get round the buffering in a round about way by allowing you to pause the feed...let it download and then restart the feed?
That's what I meant by the last part of my post. You can pause and let it buffer before watching, but the amount of time it needs to buffer is going to be the same, just broken up over the course of playback, or all at the beginning.
The other major problem aside from running out of RAM, is if you fill up your buffer, XBMC stops pulling information from the server until there's more room in the buffer. Some sites won't let you resume a download like this (this is a common way to encourage people to get premium accounts). That means that once your buffer fills up, it breaks the connection and the website doesn't let it start again so when you play through your buffer xbmc thinks that's all there was to the file and goes back to the menu just like playback had finished normally.
In the end, no one can give you a magic number because it's going to depend on how much RAM you have available at any given time. Your available RAM is influenced by everything you do: What skin you use, what you have running in the background, what addons you have installed, what kind of media you're playing, the encoding of the media you're playing, etc. Since the atv doesn't have much ram to spare to begin with (256mb), I recommend letting sleeping dogs lie and let xbmc handle the buffer. If you're on a full desktop with plenty of RAM, then you can take advantage of that by upping the limit.
Let's say for example you're able to dedicate the full 256 mb of RAM to the buffer (which is impossible, but makes the point). XBMC uses 3 times the RAM for buffering, so you could buffer a maximum of 85mb of a file. Lets say also for example that you have a 10mb internet connection and that you're able to get full speed all the time (also not going to happen). The buffer would fill up in 68 seconds. Is it really worth all that math and tweaking and crashing to possibly save yourself 68 seconds?