I remember noticing a few years ago that my Windows Media Encoder update no
longer automatically created .asf files. When I look back at my archived
web videos I see that after a certain point all of them were .wmv. I
believe the reason for this is that .asf files are interchangeable with
.wmv and .wma files, but the latter tell you something about themselves
(video versus audio) whereas .asf could be either. My guess is that
Microsoft made the switch when they began to invest in developing the audio
format with song downloads in mind.
What determines how a windows media video plays on the web is the type of
server hosting it. You can offer video on a web server or a media server.
My stuff is on a web server. This means it is sent in packets like any
other file transfer, with error checking ensuring that all packets are
received. This can be a problem for video, as it can be held up waiting for
data that's taken a wrong turn, although in practise it works very well for
fewer than a dozen simultaneous connections. A media server makes a two-way
connection with the visitor's computer and manages the stream throughout
the connection. It also leaves no temp file so the content remains
relatively secure. A multi-data rate file on a media server will deliver
according to the connection speed of each specific visitor. The same file
on a web server will deliver at the highest rate encoded in the file. This
wastes bandwidth and large commercial or educational web video providers
try not to do that, given what they pay for it. Both web and media server
video begins to play as soon as enough of the file is buffered. If the
bandwidth available to a viewer becomes constricted during playback a media
server will recognize this and lower the data rate. A web server will not,
because it it just talks, it doesn't listen. When you see a Windows Media
Internet video address beginning in http:// you know it's on a web server.
When it starts with mms:// it's on a media server.
Files like .asx and .wmx are called stream redirectors. They have two
functions. The simplest is to contain the address of the media file, while
at the same time telling the operating system to bring up the Windows Media
Player. They can also contain instructions regarding playlists, for
example, and banners to insert within the player window. This extra level
of function is only available with media server hosting.
David Hurdon
At 03:20 AM 4/11/2005 -0700, you wrote:
Even better stuff, Jeff, thanks. I'll definitely have to try that.
-Frank
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