Video Editing on Low End Macs
Part 1: Software, Compression, and Hardware
Dave Ip - 2001.08.20
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.
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.
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.
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.
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.
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