On 1/18/11 4:37 PM, Glenn Maynard wrote:
If you don't have enough bandwidth, then the necessary buffer size is
effectively the entire video[1]
No, it's really not. Your footnote is, of course, correct.
If my bandwidth is such that I can download the video in 2 hours, and
it's one hour long, then letting me start playing after 1.5 hours of
downloading seems perfectly safe to me, if the download speed is stable
enough (has a 2x margin of safety).
If the download speed is not stable enough, then it doesn't matter
whether on average you can stream the video, because the outliers will
still kill you.
Mikko seems to suggest that it's the
entire video times some multiplier, where that multiplier can be
discovered by binary searching.
The multiplier should just be a function of the ratio of the stream
bitrate and the available download bandwidth if those are both constant.
But note that available download bandwidth is non-constant. A number of
cable services around here, at least, seem to do something where they
give you N bytes per second for the first K bytes of a download
(presumably that's a single connection, but who knows how they define
it) and N/2 or N/3 or N/10 bytes per second for the rest of the
download. The connection is sold as an N/2 or N/3 or N/10 connection,
not a connection that can actually produce N bytes per second. But
nevertheless, the average download rate will differ depending on the
file size, and hence the multiplier is different for different file sizes.
Given that I think the random speedup bit is per-connection, I doubt
that this can be discovered with some sort of binary search, though.
Agreed on that.
-Boris
