14 Apr
2009
14 Apr
'09
10:18 p.m.
On Sat, Apr 11, 2009 at 10:20 PM, Asiri Rathnayake <
asiri.rathnayake(a)gmail.com> wrote:
I was thinking of a usecase where users can play an
attachment for an
example.
I'm pretty new to streaming content, but to enable streaming of attachments
(audio, video) we would have to store them on files instead in database
entries right? and then may be we can use JMF (
http://java.sun.com/products/java-media/jmf/index.jsp) for streaming.
If you're playing back an Xwiki attachment as streaming media, there's
plenty of problems because the entire stack is not designed for streaming...
On the server-end, things are limited not by Xwiki itself, but by the use of
Java and Servlets, which ends up being incredibly heavy-weight for streaming
large data files. The issue with large-files and streaming media (e.g.
video) is that the "download" happens over a very long period of time;
streaming playback by definition means you're not downloading entire files
before play-back; instead, you use a small buffer and hope that network can
keep the buffer filled while the data plays back at a slow "real-time"
data-rate.
Even if xwiki's db access could be made "incremental" or "paged",
with
multiple users streaming simultaneously, a java/servlet based system
requires huge amounts of overhead per connection. It's easy to run out of
memory, or max-threads. The worst part about this architecture, as opposed
to more traditional practices in C/C++ using
select()<http://en.wikipedia.org/wiki/Select_%28Unix%29>and
nonblocking
I/O<http://en.wikipedia.org/wiki/Non-blocking_I/O#Select.28.2Fpoll.29_lo…ps>,
is that most of those threads are basically doing *nothing* most of the
time, and when they are, they are sending out packet of data and then going
back to sleep... Of course, the servlet spec allows streaming, and there are
implementations of servlet-streaming that are quite straightforward to
implement, but may have performance/overhead issues anyways in real-use,
e.g.:
http://www.longtailvideo.com/support/forum/Modules/14410/Servlet-Streaming
IMHO, the leading implementations are still in C/C++ -- just find one that's
active, mature, and widely used, treat it as a black box, and use whatever
combination of arcane configuration commands needed to get it integrated:* *The
most interesting option for Xwiki integration is
mod_h264_streaming<http://h264.code-shop.com/trac/>since it would run
in Apache and many already "front" their Xwiki with
apache and mod_jk. (This option might provide and easier
authentication&access-control integration w/ Xwiki). Some other standalone
implementations include: Darwin Streaming Server by
Apple<http://developer.apple.com/darwin/projects/streaming/>g/>,
ViTooKi <http://vitooki.sourceforge.net/>,
Catra<http://www.catrasoftware.it/Streaming/CatraStreamingPlatform.htm>.
Those might do the job better for managing a site full of streaming
servers, but may be harder to integrate.
I haven't looked at JMF solution for streaming.... nor do I see anything
about it that would make the task easier or the issues I mentioned go away.
Please let us know what you find out regarding JMF's performance and
integration capabilities!
Niels
http://nielsmayer.com