Windows Media: Encoding and Serving
April 9, 2001
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In our
last article we discussed how to shoot video that will
eventually be streamed on the Web. Once this video was shot it
was converted into an
AVI
file using an encoding card and should now be residing safely on
your hard drive awaiting the next step: encoding.
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The AVI file you have encoded is very large compared to the size
of the finished encoded file because it has not been compressed
by the codec. As you can see encoding a large number of AVI
source files will quickly fill up the hard drive on the average
computer. If you plan on doing a large amount of encoding
yourself you should seriously think about your storage needs
before you get started.
Storage and Backup:
Storing AVI files is only half the battle. You also need to make
sure that a hard drive failure doesn't wipe out all that hard
work. If you thought shooting the video and encoding it to AVI
was time consuming the first time, try doing it twice. In order
to protect this investment there are several things you can do to
increase storage and backup.
Easy and Cheap
If you're only running a small operation the cheapest solution is
to maintain a large hard drive on your encoding computer. Only
keep a limited number of AVIs on this machine at any one time.
Any AVIs you are done working on should be dumped to CD-R or to a
tape backup machine. CD-Rs will hold between 650 and 700 MB while
a tape backup will hold 40GB in compressed mode. CD-Rs are now
less than $1/CD and backup tapes are also cheap, small and
durable. With this method a drive failure will cause you to loose
your current project, but all other projects are backed up.
Medium
Hard drives are cheap and getting bigger and cheaper every day.
If you'd like to keep more of your AVI files online instead of in
a storage rack then consider RAID. RAID means "Redundant Array
of Inexpensive Disks". There are various levels of RAID, but
what they all have in common is taking the cheap drives available
today and making a storage solution that is large and dependable.
Let's see the various levels.
RAID-0: This level of RAID does not give you any
protection from hard drive failure and is not recommended. It
takes several small drives and makes them into one large
partition using "striping". If one drive goes down you lose
everything off all the disks because the data is scattered across
them randomly.
RAID-1: I use this on standalone encoding machines. In this
version of RAID two identical hard drives "mirror" their content.
If one fails no data is lost. A new drive can be substituted for
the failure and the data will be automatically replicated from
the remaining good drive. This technique can reduce drive failure
to almost zero.
RAID-5: In this model you can use many drives to create a
large partition as with RAID-0. However with RAID-5 a single
drive failure does not destroy the whole system. Extra
information is stored across all the drives so that if one fails
the data can be collected from the others to rebuild the failed
drive. RAID-5's principle advantage over RAID-1 is that it offers
redundancy and protection against single-drive failure, while
offering far more storage capacity when used with three or more
drives.
Expensive:
The most expensive solution is NAS (Network Area Storage).
This is used in a situation where you have multiple encoding
machines. In this case they would all share a common storage area
for all their data. The data could then be shared across all the
machines and could be backed up. NAS solutions are provided by
Network Appliance and
EMC.
Why is it so important to save your AVI files after they have
been encoded to Windows Media? Can't you just throw them away?
With the rapid change in streaming media it is always a good idea
to hold onto your "source file".
Say you encode at 56kb/s today for dial-up users and throw away
your AVI files. What happens when your audience shifts to DSL
lines or cable modems? They won't be content with 56kb/s. They
will want 300 kb/s or higher. If you have the source AVI you can
just re-encode at a higher bandwidth.
It is my feeling that eventually you will only maintain the
source file and that servers will get fast enough to encode the
source file into the proper format and bandwidth on the fly for
the end user. This should eliminate all the manual labor
associated with encoding.
Encoding - Page 2
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