The HLS spec (
http://tools.ietf.org/html/draft-pantos ... reaming-03) requires that there always be at least three segments in the playlist at all times. The spec recommends that each segment be 10 seconds long, but some providers have chosen to use shorter segments, down to 5 seconds. We'd recommend careful testing if you choose a segment size less than the recommended 10 seconds. The Roku player does download and buffer a certain amount of data before playback begins. The exact amount downloaded depends on the measured network bandwidth, but it's shorter for HLS than for any other media format.
--Mark