User`s guide

36 Chapter 4 Advanced Concepts
Compressing Movies for Streaming (Hinting)
If you want to stream a QuickTime movie using QuickTime Streaming Server, you
should use a web-optimized video or audio compressor to compress the movie file.
“Hinting” creates a hint track for every streamable track in a movie; the streaming
server uses the hint tracks to turn the media into real-time streams.
All QuickTime compressors are compatible with QuickTime Streaming Server, but the
compressors listed here are optimized to give the best results for delivery over the
Internet. For a complete list of compressors that QuickTime supports, see the
QuickTime website.
Video compressors: MPEG-4, Sorenson Video (any version), H.261, H.263
Audio compressors: AAC, QDesign Music, QUALCOMM PureVoice
Setting Data Rate Options for Video Compression
When you export a QuickTime movie, you can set the data rate for most compressors,
such as MPEG-4 and H.263. The data rate is the amount of data played per second,
usually measured in kilobytes per second or kilobits per second. The data
rate of a movie is also affected by other compression options you set, such as the
frame rate.
You may want to set a data rate based on the way your movie will be viewed. For
example, for viewing over 56K Internet dialup connections, you need to limit the data
rate to a maximum of 36 kilobits per second.
Setting Key Frame Options for Video Compression
In most cases, QuickTime uses “frame differencing” to compress moving images. Frame
differencing is the process of determining what information has changed from a
starting frame (called a “key frame”) to subsequent frames. The key frame contains all of
the information for an image. Subsequent frames contain only the information that has
changed.
Depending on the compressor you use, you can specify how often you want key
frames to occur. If you don’t have enough key frames, the quality of your movie might
be lower because most frames are generated from others. On the other hand, more key
frames result in a larger movie with a higher data rate. With some compressors, an
additional key frame is inserted automatically if too much of the image has changed
from one frame to the next.
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