Good job.

As pretty much everyone on here has heard me say before though, choosing PHP to code some application in which has large amounts of data handling and transfer isn't the best idea. Either way you do it, it'll use quite the amount of memory compared to other languages.

Also do note that download accelerators (in theory, technically) are completely useless unless the server you're downloading from forces some speed limit. Downloading some file at your full speed is obviously going to be the same speed as downloading that same file in multiple streams.

Like I said though, good job.

P.S. Best part of that code is the regex, even if you didn't write it yourself, just because regex is awesome (I wrote 30 lines of it yesterday).