Preparing source material
Video capture and compression are time-consuming, so prepare source
material carefully. Typical source materials include:
- your own video
- film- or video-based material from video tape or laser disc
- computer animations
Keep in mind that storage becomes an issue as soon as you get into the
digital world. Each second of video takes about 5 minutes of processing
time and requires 30 MB when digitized. Don't expect to capture first and
edit later; instead, edit your beta tapes as far as possible before
compressing them. Try to digitize only the material you need-but use the
highest quality possible.
Securing a master copy
Make a copy of your source material to use as a "working master," and for
dubbing working copies. Store the original in a safe place. Remember that
during capture each segment of the video is played multiple times, which
can result in degradation of the quality.
Shooting your own video
Plan your shoot or select your video carefully. Advice on producing
materials that compress well is provided in the section "Will It Compress
Well?" later in the chapter. The following tips apply to shooting your own
video:
- Determine the final frame rate before shooting so you can shoot at a
lower frame rate, thus decreasing the disk space you'll need.
- Reuse a single segment, if possible. For example, tile 10-second
pieces of moving water for longer stretches.
- Use high-quality equipment, such as Betacam SP.
- Be prepared to deal with interlace effects in moving from analog
(double-buffered) to digital video. You can deinterlace using linear
interpolation with edge following, as discussed below.
Preparing film source material
Many videos started out as film; using video derived from film requires
special consideration, because the Telecine process inserts composite
frames into the video. Also, eliminate as much
noise as possible to minimize problems during compression.
Understanding the Telecine process
When producing video from film source material, studios use the Telecine
process to transfer the source material from celluloid to magnetic tape,
and from 24 fps to 30 fps. Telecine conversion is explained in detail in
Chapter 5, "Video Tools," in the section "The 3-2 Pulldown tool."
Will it compress well?
When preparing source material, keep in mind certain factors that can
affect how well or how badly the material compresses.
Eliminating noise
Most films have noticeable film grain noise and scratches. To the
compression tool this noise is significant, and is maintained or even
emphasized during compression. Therefore, you should remove as much of it
as possible before compression. Below are several options for reducing
film grain noise:
- A post-production studio can clean up analog film.
- If your source is film, reduce grain noise using a median or recursive
noise filter, which picks out sharp anomalies like spots or pops.
- On D1, D2, or D3 video, a digital filter can be used right after the
Telecine process.
- Low-light shoots generate more film or video noise. Three CCD
(couple-charged device) cameras generate less video noise.
Edge crawl
Jagged edges cause edge crawl on TV monitors. Edge crawl can be caused by
uneven resizing or aliasing, so always use anti-aliasing resizing.
Other considerations
Bear in mind that:
- A source with constant backgrounds and solid colors yields the best
results.
- Slow color gradients cause color banding when compressed with Cinepak.
- Slow pans/zooms are difficult to compress well.