The Data-Rate Settings Request Type
Use the data-rate settings request to retrieve or modify the current temporal compression parameters that govern the data rate. These parameters affect sequence-compression operations.
You supply a pointer to a data-rate settings structure. If you are retrieving these settings, the standard dialog component places the current settings into the specified structure; if you are changing the settings, place the new values into the structure--the component uses those values to update its settings.
The
SCDataRateSettings
data type defines the format and content of the data-rate settings structure:
typedef struct {
long dataRate; /* desired data rate */
long frameDuration; /* frame duration */
CodecQ minSpatialQuality; /* minimum value */
CodecQ minTemporalQuality; /* minimum value */
} SCDataRateSettings;
-
dataRate
-
Specifies the maximum number of bytes of compressed data your application wants to receive per second. Use this parameter to modulate the rate at which the component passes compressed data to your application. This can be useful to account for hardware limitations during sequence playback.
-
frameDuration
-
Indicates the duration of each frame, in milliseconds. Set this parameter to 0 to allow the standard dialog component to calculate the duration based upon the frame rate you specify in an
scTemporalSettingsType
request. However, if you allow the user to specify a 0 frame rate (that is, you set the
scAllowZeroFrameRate
flag to 1 in your
scPreferenceFlagsType
request), you must set the frame duration each time you compress a frame, because the component does not have sufficient information to determine an appropriate rate.
-
minSpatialQuality
-
Specifies the minimum acceptable spatial quality. In order to meet your specified data rate, the standard dialog component may have to adjust the spatial quality setting. Use this parameter to set a minimum level, which the component may not exceed. See the chapter "Image Compression Manager" in Inside Macintosh: QuickTime for values for both this parameter and the
minTemporalQuality
parameter.
-
minTemporalQuality
-
Specifies the minimum acceptable temporal quality. As with spatial quality, in order to meet your specified data rate, the standard dialog component may have to adjust the temporal quality setting. Use this parameter to set a minimum level, which the component may not exceed.
© 1997 Apple Computer, Inc.Previous | Chapter Top | Chapter Contents | Next
