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AV Foundation Framework Reference AVAudioMixInputParameters Class Reference

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AVAudioMixInputParameters

An AVAudioMixInputParameters object represents the parameters that should be applied to an audio track when it is added to a mix.

You use an instance AVAudioMixInputParameters to apply audio volume ramps for an input to an audio mix. Mix parameters are associated with audio tracks via the trackID property.

Audio volume is currently supported as a time-varying parameter. AVAudioMixInputParameters has a mutable subclass, AVMutableAudioMixInputParameters.

Before the first time at which a volume is set, a volume of 1.0 used; after the last time for which a volume has been set, the last volume is used. Within the time range of a volume ramp, the volume is interpolated between the start volume and end volume of the ramp. For example, setting the volume to 1.0 at time 0 and also setting a volume ramp from a volume of 0.5 to 0.2 with a timeRange of [4.0, 5.0] results in an audio volume parameters that hold the volume constant at 1.0 from 0.0 sec to 4.0 sec, then cause it to jump to 0.5 and descend to 0.2 from 4.0 sec to 9.0 sec, holding constant at 0.2 thereafter.

Given that this is an immutable variant of the object, you should not allocate and initialize a version of this class yourself. Other classes may return instances of this class.

  • Obtains the volume ramp that includes the specified time.

    Declaration

    Swift

    func getVolumeRampForTime(_ time: CMTime, startVolume startVolume: UnsafeMutablePointer<Float>, endVolume endVolume: UnsafeMutablePointer<Float>, timeRange timeRange: UnsafeMutablePointer<CMTimeRange>) -> Bool

    Objective-C

    - (BOOL)getVolumeRampForTime:(CMTime)time startVolume:(float *)startVolume endVolume:(float *)endVolume timeRange:(CMTimeRange *)timeRange

    Parameters

    time

    If a ramp with a time range that contains the specified time has been set, information about the effective ramp for that time is supplied. Otherwise, information about the first ramp that starts after the specified time is supplied.

    startVolume

    A pointer to a float to receive the starting volume value for the volume ramp.

    This value may be NULL.

    endVolume

    A pointer to a float to receive the ending volume value for the volume ramp.

    This value may be NULL.

    timeRange

    A pointer to a CMTimeRange to receive the time range of the volume ramp.

    This value may be NULL.

    Return Value

    YEStrue if the values were retrieved successfully, otherwise NOfalse. Returns NOfalse if time is beyond the duration of the last volume ramp that has been set.

    Discussion

    The process of setting up volume ramps requires the configuration of an instance of AVMutableAudioMixInputParameters.

    Availability

    Available in iOS 4.0 and later.