Game Development Reference
In-Depth Information
Streaming Video and Compression
Each video frame in your cinematic should pass through compression only once. Every
compressionpasswi ldegradetheartquality.Provethistoyourselfbycompressinga
pieceofvideotwoorthreetimes,andyou
'
ll see how bad it gets even with the second pass.
USB Hard Drives and FedEx
If you need to move a large data set like uncompressed video from one
network to another, use a stand-alone Ethernet or high-speed USB-capable
hard drive.
sa
useful alternative to burning a stack of DVDs or worse, trying to send a few
hundred gigabytes over the Internet. This is modern day
It might make security-conscious IT guys freak out, but it
'
“
Sneakernet.
”
Don
t waste your time backing up uncompressed video files. Instead, make
sure that you have everything you need to re-create them, such as a 3ds
Max scene file or even raw videotape. Make sure the source is backed up
and the final compressed files are backed up.
'
If you need to regenerate
them, just press the
“
animate
”
button and wait a few hours.
Compression settings for streaming video can get complicated. Predicting how a set-
ting will change the output is also tricky. Getting a grasp of how it works will help
you understand which settings will work best for your footage. Video compression
uses two main strategies to take a 5GB two-minute uncompressed movie and boil it
down into a 10MB or so file. Just because the resolution drops doesn
'
t mean you
have to watch a postage stamp-sized piece of video. Most playback APIs will allow
a stretching parameter for the height, width, or both.
The first strategy for compressing video is to simply remove unneeded information by
reducing the resolution or interlacing the video. Reducing resolution from 800 × 600
to 400 × 300 would shave 3GB from a 4GB movie, a savings of 75 percent. An inter-
laced video alternates drawing the even and odd scanlines every other frame. This is
exactly how television works; the electron gun completes a round trip from the top of
the screen to the bottom and back at 60Hz, but it only draws every other scanline.
The activated phosphors on the inside of a CRT persist longer than 1/30th of a second
after they
'
ve been hit with the electron gun and can therefore be refreshed or changed
at that rate without noticeable degradation in the picture. Modern displays aren
'
tso
forgiving, but remember that the human eye generally perceives continuous move-
ment between 30 and 60fps, but since human vision is not frame based, this is highly
dependent on the content being reproduced. As always, removing data will result in a
degradation of perceived quality. Interlacing the video will drop the data set down to
one-half of its original size. Using interlacing and resolution reduction can make a
huge difference in your video size, even before the compression system kicks in.
