there is a solution to the first post.
you CAN use a comma in a filename. but you have to url-encode it. two times.
comma url encoded is %2C. but flash decodes it and flash script receives value decoded to actual comma and then splits string using that comma as a separator. to avoid this we “escape” that %2C, that is we encode it another time and get %252C. in that case flash decodes to %2C and the flash script does not split it. then %2C remains in url until player asks server for that file.
example from my code:
$filename = MEDIASERVER . str_replace(",", "%252C", str_replace(" ", "%20", $filename));
good luck
