Printing to Video

The Final Product

Although it is tempting to concentrate only on making a movie look as good as possible, you must discipline yourself and constantly keep in mind the limitations of your system in terms of playback of your final movie file. It is absolutely essential to have your final product playback perfectly smoothly. You can have stunning images and breathtaking effects, but if there are jerks in the playback, your movie will end up looking very amateurish. You need to think about the final product before even touching the first image. If you don't, you will end up retracing many of your steps and wasting many hours of time. It requires a good feel for the capabilities and/or limitations of your system and a knowledge of the many file-specific factors that affect playback. These factors are: file size, frame size or resolution, color depth, frame rate, and compression format. In a perfect world, your digital video workstation would have unlimited hard drive space, unlimited memory, and an infinitely fast data bus. That way, you could work with files that are 640x480 (maximum NTSC resolution), 24-bit color (beyond maximum color depth that the human eye can differentiate), 30 frames per second (beyond maximum frame speed that the human eye can differentiate), and uncompressed (for maximum image quality). But no one works in a perfect world and everyone must cut corners somewhere to make their movies play smoothly. There is no set of criteria for where the corners must be cut. It depends entirely on the situation and it requires a good knowledge of all the previously named factors. What follows is a detailed description of all those that factors affect playback of QuickTime movies.

Hardware-specific factors that affect playback of QuickTime movie files:

CPU speed:
The speed of the CPU most affects movies that are compressed using computationally intensive compression formats (or codecs) such as JPEG. The faster the CPU can decompress the movie, the faster it can be displayed on the screen. Problems of this type can be solved by compressing the file in a different format such as animation (see my notes on compression formats below).

Hard Drive/Data Bus Speed:
Unless you can fit the entire movie file into RAM (which is rarely the case), you will have to spool the movie file off the hard drive. If the data cannot be transferred from the hard drive to the CPU fast enough, there will be jerks in the playback as the CPU waits for the data. In most cases, this is where playback problems occur. Slow data buses can only be sped up by purchasing SCSI accelerator boards and faster hard drives that can keep up with them. The SCSI buses in standard macs are SCSI-1 buses which have a maximum throughput of 5mb/sec. SCSI-2 buses (found in PowerMac models 7500, 7600, 8500 and 9500) can transfer data at 10mb/sec. There is also SCSI-3 which is able to transfer data at 20mb/sec. In terms of the movie file, high data rates can be decreased by decreasing the frame rate, decreasing the color depth, decreasing the frame size, or choosing a compression format that compresses smaller, such as JPEG or cinepak.

Memory:
Good QuickTime movie players, such as PetersPlayer are able to use memory very efficiently so that as little of the movie is spooled off the hard drive as possible. Movie files that are printed to video can get very large and they are usually too large to fit completely into RAM, but the more RAM you have the better off you are.

Hardware Compression/Decompression:
There are many 3rd party video boards that contain microprocessors whose sole reason for being is to perform all the calculations necessary for compression and decompression of movie files. Since the CPU does not have to worry about these calculations it is free to make sure everything else is running smoothly. The best results are achieved with these boards. They enable you to use a very good quality and low-file-size compressor such as JPEG and still play smoothly. The main obstacle for their use is cost.

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