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Data rates
The data rate affects the quality of a video clip and the audience that can download the file
given their bandwidth constraints.
When you deliver video using the Internet, you should produce files using lower data rates.
Users with fast Internet connections can view the files with little or no delay, but dial-up users
must wait for files to download. If you anticipate an audience of dial-up users, you should
make short video clips to keep the download times within acceptable limits.
Flash Video Encoder lets you specify data rate settings for encoding video at a low, medium,
or high quality. If the available settings in the Quality pop-up menu do not produce the
desired results with your particular source footage, select Custom, and enter a higher data rate
in the Maximum Data Rate text box.
Keyframes
Keyframes are complete video frames (or images) that are inserted at consistent intervals in a
video clip. The frames between the keyframes contain information on movement and scene
changes that occurs between keyframes. For example, if a video depicts a person walking past
a doorway, the keyframes contain the complete image of the person and the door in the
background, and the interval frames contain information describing the person's movement as
they walk in front of the door.
By default, Flash Video Encoder automatically determines the keyframe interval to use based
on the video clip's frame rate. The keyframe interval value tells the encoder how often to re-
evaluate the video image and record a full frame, or keyframe, into an FLV file. In Flash Video
Encoder, this setting is the keyframe interval value, which represents the number of frames
between keyframes. Flash Video Encoder approximates frames that reside between keyframes
by estimating the full value of all pixels on the screen by comparing multiple frames and
eliminating redundant information.
The keyframe interval value can be any number up to 100. When you select Automatic as an
interval setting, Flash Video Encoder places a keyframe every two seconds of playback time.
For example, if the video you're encoding has a frame rate of 30 fps, a keyframe will be
inserted every 60 frames. In general, the default keyframe interval value provides a reasonable
level of control when seeking within a video clip. If you need to select a custom keyframe
placement value, be aware that the smaller the keyframe interval, the larger the file size.
If your footage has a lot of scene changes or rapidly moving motion or animation, then the
overall image quality may benefit from a lower keyframe interval. In general, a higher
keyframe interval produces better image quality because data is not wasted describing the
areas of an image that remain unchanged from frame to frame.
10
Using Flash Video Encoder
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