The AudioChannelDescription Core Audio structure contains all the information for describing a single audio channel.
The QTPlgAudioChannelDesc class provides you with properties and methods that let you whether access or create new instances of such a Core Audio description structure. You will use instances of this class to add to or retrieve channels from a class instance.
This class requires QuickTime 7 or later.
The QTPlgAudioChannelDesc class constructors are called when you create a new instance of the class, while the ˜QTPlgAudioChannelDesc class destructor, is called automatically when the class is no more in use. Also, you can invoke the class destructor by setting the instance of the class to nil.
Once a new class instance is returned, it is good practice to check the class property to be sure that the new object can be used.
The class provides you with the following initializer methods:
()
This is the default constructor. Use this constructor to create a completely new data descriptor container in memory
(other as QTPlgAudioChannelDesc)
This is the copy constructor. The properties of the object to be copied will be used to initialize the
new class instance properties
returns a pointer to the built–in AudioChannelDescription Core Audio structure; useful for Toolbox programmers
(use with care: you could invalidate the handle causing unpredictable results
(probably an application crash))
determines if the channel is in use. If this property is set to false, the channel is present, but has no intended use or destination
specifies if the channel is described by the values. If this property is set to
false, the channel is described by the value of the property
determines the units of the values are in meters. If this property is set to
false, the units are relative to the unit cube or unit sphere
an integer value that describes the channel
identifies the type of the coordinate system that has to be used to interpret the values of the
class property. This property accepts only values listed in the
section below
specifies the number of coordinates settable by the class property; actually,
this property is set to 3
a zero–based array of coordinates (that is i ranges from 0 to
–1)
that identify a precise speaker location. The meaning of the array values depends on the type of coordinates specified by the
property
the type of coordinate is unknown; this being the case, the values returned from the
class property are meaningless
the channel is specified by the cartesian coordinates of the speaker position; this being the case, the values of the
array assume the following meaning:
- coordinate[0]: left–right position (negative is left and positive is right)
- coordinate[1]: back–front position (negative is back and positive is front)
- coordinate[2]: down–up position (negative is below ground level, 0 is ground level, and positive is above ground level)
the channel is specified by the spherical coordinates of the speaker position; this being the case, the values of the
array assume the following meaning:
- coordinate[0]: azimuth (0 is front center, positive is right, negative is left. Values are expressed in degrees)
- coordinate[1]: elevation (+90 is zenith, 0 is horizontal, –90 is nadir. Values are expressed in degrees)
- coordinate[2]: distance (the units are determined by the class property)