Struct AVAudioConverterPrimeInfo

#[repr(C)]
pub struct AVAudioConverterPrimeInfo {
    pub leadingFrames: AVAudioFrameCount,
    pub trailingFrames: AVAudioFrameCount,
}

Available on crate features AVAudioConverter and AVAudioTypes only.

This struct is the value of the primeInfo property and specifies priming information.

When using convertToBuffer:error:withInputFromBlock: (either a single call or a series of calls), some conversions, particularly involving sample-rate conversion, ideally require a certain number of input frames previous to the normal start input frame and beyond the end of the last expected input frame in order to yield high-quality results.

These are expressed in the leadingFrames and trailingFrames members of the structure.

The very first call to convertToBuffer:error:withInputFromBlock:, or first call after reset, will request additional input frames beyond those normally expected in the input proc callback to fulfill this first AudioConverterFillComplexBuffer() request. The number of additional frames requested, depending on the prime method, will be approximately:

Prime method	Additional frames
AVAudioConverterPrimeMethod_Pre	leadingFrames + trailingFrames
AVAudioConverterPrimeMethod_Normal	trailingFrames
AVAudioConverterPrimeMethod_None	0

Thus, in effect, the first input proc callback(s) may provide not only the leading frames, but also may “read ahead” by an additional number of trailing frames depending on the prime method.

AVAudioConverterPrimeMethod_None is useful in a real-time application processing live input, in which case trailingFrames (relative to input sample rate) of through latency will be seen at the beginning of the output of the AudioConverter. In other real-time applications such as DAW systems, it may be possible to provide these initial extra audio frames since they are stored on disk or in memory somewhere and AVAudioConverterPrimeMethod_Pre may be preferable. The default method is AVAudioConverterPrimeMethod_Normal, which requires no pre-seeking of the input stream and generates no latency at the output.

Field: leadingFrames Specifies the number of leading (previous) input frames, relative to the normal/desired start input frame, required by the converter to perform a high quality conversion. If using AVAudioConverterPrimeMethod_Pre, the client should “pre-seek” the input stream provided through the input proc by leadingFrames. If no frames are available previous to the desired input start frame (because, for example, the desired start frame is at the very beginning of available audio), then provide “leadingFrames” worth of initial zero frames in the input proc. Do not “pre-seek” in the default case of AVAudioConverterPrimeMethod_Normal or when using AVAudioConverterPrimeMethod_None.

Field: trailingFrames Specifies the number of trailing input frames (past the normal/expected end input frame) required by the converter to perform a high quality conversion. The client should be prepared to provide this number of additional input frames except when using AVAudioConverterPrimeMethod_None. If no more frames of input are available in the input stream (because, for example, the desired end frame is at the end of an audio file), then zero (silent) trailing frames will be synthesized for the client.

See also Apple’s documentation

Fields

leadingFrames: AVAudioFrameCount

trailingFrames: AVAudioFrameCount

Trait Implementations

impl Clone for AVAudioConverterPrimeInfo

fn clone(&self) -> AVAudioConverterPrimeInfo

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for AVAudioConverterPrimeInfo

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Encode for AVAudioConverterPrimeInfo

const ENCODING: Encoding

The Objective-C type-encoding for this type.

impl PartialEq for AVAudioConverterPrimeInfo

fn eq(&self, other: &AVAudioConverterPrimeInfo) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl RefEncode for AVAudioConverterPrimeInfo

const ENCODING_REF: Encoding

The Objective-C type-encoding for a reference of this type.

impl Copy for AVAudioConverterPrimeInfo

impl StructuralPartialEq for AVAudioConverterPrimeInfo