Video Codecs Supported Within Video File Formats
A video codec is an algorithm for encoding video images in space (within a frame) and
time (across multiple frames) to compress the data requirements while still producing
an acceptable image. Not all codecs are supported by all file formats.
This isn’t really a codec, but a way of storing QuickTime movies with no compression at
all. Since applying compression generally results in video artifacts, no compression
guarantees the highest quality. Unfortunately, it also guarantees enormous file sizes,
and they will not play back in real time on most systems.
Learning About QuickTime
Uncompressed movies can have an alpha channel. Alpha channels define levels of
transparency in your movie and are useful if you’re delivering an effects shot for use in
someone else’s composition. For more information on alpha channels, see Volume III,
Chapter 19, “Compositing and Layering.”
The Animation codec was developed for computer-generated imagery, which often has
large areas of uniform color and little, if any, noise. It is a lossless codec, which means it
doesn’t degrade quality or add artifacts to your video when it applies compression. For
more information, see “
” on page 391.
Video footage, which generally has more grain, noise, and variations of texture and
color than animated material, may not be compressed as much with the Animation
codec as with other methods. Because some lossless compression is better than none,
this codec is used more frequently than Uncompressed.
Note: Animation movies will not play back in real time on most systems. Animation
movies can also have an alpha channel.
QuickTime supports a wide range of DV codecs, including DV NTSC and DV PAL,
DVCPRO 50, and DVCPRO HD. This allows you to natively capture, edit, and playback
footage from DV camcorders without first transcoding to another format.
There are two Apple M-JPEG codecs, M-JPEG A and M-JPEG B. These are variable data
rate codecs similar to the ones used by video capture cards. If you need to deliver more
heavily compressed material to keep files small, consider these codecs. M-JPEG is a
“lossy” codec (meaning visual information is permanently removed from the video
frames) and will result in artifacts in your video. The severity of these artifacts depends
on the data rate you choose.
Several video interface cards on the market can play back either M-JPEG A or M-JPEG B
in real time without rerendering the material, or, at most, doing minimal rerendering.
This makes file interchange very fast. Before you use either M-JPEG A or B, consult the
manufacturer of the capture card you’re using to find out which one you should use.
Note: Apple M-JPEG movies cannot have alpha channels.
JPEG is similar to M-JPEG, except that the compression artifacts can be less severe at
similar data rates. JPEG movies may play back in real time on your system, depending
on your system’s capabilities and the data rate of the movie.
Note: JPEG movies cannot have alpha channels.
There are several manufacturers of video-editing solutions, most of whom use different
variations of the M-JPEG codec. Many make software-only QuickTime codecs that you
can install on your system, enabling you to play back movies with little or no
rerendering. For more information, contact the manufacturer of the editing system.
Note: Most third-party codecs cannot have alpha channels.