Purchasing a new Mac for digital video editing is a no-brainer:
With FireWire ports and iMovie software, it's simpler than ever to
make your own movies.
If you've got an analog video camera and an older Mac, you can
still capture and edit your own movies. A high quality video camera
combined with an AV Mac can also make an inexpensive digicam or
webcam. They may be discontinued, but some older Macs remain viable
and capable machines if your requirements (and expectations) aren't
too high.
Big Fast Hard Drives
Video capture and editing is extremely computer
intensive, requiring a fast hard drive, gobs of processing power,
and lots of RAM. In general, the slower the computer, the lower the
quality of the captured video. Uncompressed, full motion video (30
frames per second) at 320 x 240 resolution can consume almost 400
MB of drive space per minute:
- 320 x 240 @ 24 bits = 225 KB per frame x 30 frames per second =
6.6 MB per second x 60 seconds = 395 MB per minute
For 16-bit video (thousands of colors), the requirements are a
little lower:
- 320 x 240 @ 16 bits = 150 KB per frame x 30 frames per second =
4.4 MB per second x 60 seconds = 263 MB per minute
The hard drive must be large enough to hold the video, and it
also has to be fast enough to receive the video as it is being
delivered or else quality suffers. If the hard drive can't keep up,
the result is dropped frames, which shows up as jerkiness or a lack
of smoothness in movement.
For older Macs, the SCSI bus often tops out at 5 or 10 MB per
second. This is a theoretical maximum; actual speeds may be much
less.
Newer Macs with IDE hard drives fare a bit better, depending on
the interface used (ATA/33, ATA/66, ATA/100). Again, this is an
indicator of burst speed, not sustained speed. The actual sustained
speed of the drive may be as low as 10% (or less) of the maximum
rating.
RAID and AV Drives
You can cope with the speed problem by using a RAID (Redundant
Array of Independent Disks) controller. RAID, in its simplest form,
writes data across two or more hard drives (not partitions) at the
same time, which greatly increases speed and reliability at a
higher monetary cost.
Hard drives must be selected for AV use; that is, they have to
be able to suspend (or disable) thermal recalibration. As a hard
drive spins, heat is generated in its moving parts. Once it reaches
a certain temperature, the drive may adjust its performance
(recalibrate itself) to that higher temperature. If it does this
while capturing video, an artifact may show up: dropped frames, a
white spot, a pop or click in the audio signal, etc. AV certified
drives are either designed to run at a higher temperature or to
suspend recalibration until the drive is not being accessed.
Compression
Since the video stream is so large, you can quickly run out of
space, even with today's large hard drives. To save space,
compression is used to reduce the video stream to a manageable
size. There are different types of compression used for video, with
most of the popular types falling into the "lossy" category; that
is, during compression, some of the information is lost or thrown
away.
In the simplest sense, the parts of the video that don't change
from frame to frame can be removed without a loss in perceived
quality (your eyes can't tell the difference). However, as more
compression is applied to a video signal, quality suffers, showing
up as "artifacts" - blockiness, graininess, skewed colors, etc. You
can see this in the difference between Video CDs (which use MPEG-1
compression) and DVDs (MPEG-2 compression). The MPEG-1 standard
results in smaller file sizes (approximately 10 MB per minute of
video), but it's much less efficient than the newer MPEG-2 standard
(approximately 30 MB per minute of video). A VCD is also lower
resolution than a DVD, but the difference in smoothness and color
quality is readily apparent.
Software Compression
Other types of compression (QuickTime, RealVideo, etc.) can
compress a video signal even more, at a increasing loss of quality.
Most types of compression allow you to vary the amount used to suit
your requirement: small size or high quality.
With compression, you can squeeze an hour's worth of full
motion, low resolution, VHS quality video onto a single CD. This
compression, depending on the capture card used, is often left to
the computer's main processor - this means lots of calculations per
second, requiring lots of speed and lots of RAM. If the processor
is doing the compression, it will slack in other areas (digitizing,
frame grabbing, writing to the hard drive, etc.). Quality will
suffer with slower processors that can't keep up, resulting in
lower frame rates. Faster processors will be able to handle all
functions at once, providing higher frame rates.
Hardware Compression
Better still is the addition of a hardware compression card or a
capture card that provides hardware compression. If you've played a
game like Quake or Unreal on an older Mac, you know the difference
a 3D accelerated video card (Radeon, Voodoo, GeForce, etc.) can
make: The frame rate, quality, and smoothness goes up considerably.
With a 3D accelerated video card, the computer's processor doesn't
have to handle the 3D graphics; that's left to the much faster
circuitry on the video card.
The same thing goes for a video capture card with hardware
compression; all of the video compression is done by the
specialized, fast circuitry on the card, leaving the computer's
processor to handle all other tasks. Since video capture is so
computer intensive, this can dramatically improve the quality of
captured video. Most video capture cards on older AV Macs do
not perform hardware compression, requiring the addition of
a specialized card.
Playback
If you're going to capture and edit all this great video, how
are you going to view it later on? If you want to share your video
with family and friends, you'll need some sort of writable,
removable media. You can save the video as QuickTime files for
playback on computers, using a Zip disk or recordable CD.
Recordable CD is also ideal for burning Video CDs for playback on
computers and most standalone DVD players. Software like Roxio's
Toast will setup and burn VCDs, and if you've captured high
quality, full motion video (and have the hardware) it will also
burn DVDs.
For editing, if you're going to use an older machine, you'll
have to use older software. Older versions of QuickTime are still
available from Apple, but you'll have to hunt around for editing
software like Premiere, Videoshop, etc.
If all you're doing is capturing on the older Mac, then editing
on a newer computer, the Apple Video Player (usually installed as
part of the system software) will do basic capture.
We've discussed software, compression, and hardware
requirements, but what machines are good for this sort of thing?
We'll look at that tomorrow.
