The Data-Rate Settings Request Type(IM: QC)

Inside Macintosh: QuickTime Components /

Chapter 3 - Standard Image-Compression Dialog Components / Standard Image-Compression Dialog Components Reference

Request Types

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;
Field Description

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.