Specifications
17
A Digital Video Primer
Even when the processing load is shared with or shunted to a video card (there’s more on video
cards later in this section), the performance of the CPU is still critical. In most cases, the video-
editing soware relies on the CPU to handle functions like real-time previews and transcoding
video for export. A number of computer manufacturers oer workstations specically recom-
mended for digital video editing. ere are many single and dual-processor computers that
provide appropriate CPUs as well as other important features, such as necessary I/O interfaces,
that make them well-suited to video creation and other post-production tasks.
How much RAM do you need?
First, check the system requirements for the soware you’ll be using. But keep in mind that system
requirements are typically established using a clean computer. In the real world, you’re likely to
want more than what is recommended. Some experts will tell you that when it comes to RAM,
bigger is better and biggest is best, others will say that above a certain amount, adding more RAM
is moot, a case of diminishing return on investment. But it’s always a good idea to hedge your
bets. While you may be able to struggle along with 512MB of RAM, you’ll probably be much
happier with at least 1GB. Most professionals opt for 4GB of RAM. Make sure you can add more
RAM down the road.
How much bandwidth do you need?
You’ll need to transfer the data for each frame of video to and from the processor at the video frame
rate of 29.97 fps (NTSC) regardless of how much data is contained in each frame. For uncompressed
SD video, this is approximately 1MB per frame, which translates to a data rate of almost 30 mega-
bytes per second (MBps); for HD video, it’s 6MB per frame or a data transfer rate of 180 MBps. e
transfer rate for standard DV, compressed 5:1, is approximately 5-6 MBps. Real-time editing oen
entails accessing two video streams, combining them in a dissolve, for example, and then merging the
result into a single stream. is process triples the required data rate. When you start thinking about
compositing three or more streams of video and previewing or rendering the results in real time, the
rate multiplies even more.
Video requires not only moving a great deal of data rapidly, but also at a steady, sustained pace.
If the transfer rate falls below what’s required, frames may be dropped, resulting in poor quality
video. Because systems with faster disks typically cost more, you may opt for a system that is fast
enough, but not so fast that you’re paying a premium for speed you don’t need. If you are working
with uncompressed video or HD, check the requirements for data transfer rate recommended by
the manufacturer of your video card.
How much storage do you need?
You cannot avoid the fact that digitized video is big. We’ve seen that one minute of uncom-
pressed video requires 1.5GB of storage. An hour-long program can therefore consume 90GB of
storage, without even considering all the unused footage. If a production has a 5:1 shooting ratio
(5 minutes shot for every 1 minute used), you would need to store 450GB. High-end productions
may end up with 20:1 or 50:1 ratios: 1,800GB to 4,500GB. And, for HD, you need 600GB of stor-
age per hour.
To gure the amount of storage you need for DV (compressed 5:1), you can calculate based on
approximately 216MB per minute of stored video. Or, looking at it from the opposite direction,
each gigabyte of storage holds about 4 minutes, 45 seconds of video. For an hour of DV, you
would need a 13GB disk.
Let’s say that you’re an event videographer shooting standard DV and creating DVDs for your
clients. To gure out how much storage you would need to make a two-hour DVD, here’s how
you might do the math:
Start with what you need for your finished production: two hours of DV footage 26.0GB
Add a conservative amount for unused footage, a 2:1 ratio 52.0GB
Figure in some additional elements, such as titles and audio tracks 2.0GB
You’ll also need space for the MPEG-2 files you export for your DVD 4.7GB
Total minimum storage needed 84.7GB
Example estimate of storage needed for a two-hour DVD