//! Tools for manipulating audio signals.
mod frame;
pub use frame::*;
/// Given a previous frame, a current frame, the two next frames,
/// and a position `x` from 0.0 to 1.0 between the current frame
/// and next frame, get an approximated frame.
// This is the 4-point, 3rd-order Hermite interpolation x-form
// algorithm from "Polynomial Interpolators for High-Quality
// Resampling of Oversampled Audio" by Olli Niemitalo, p. 43:
// http://yehar.com/blog/wp-content/uploads/2009/08/deip.pdf
pub fn interpolate_frame(
previous: Frame,
current: Frame,
next_1: Frame,
next_2: Frame,
fraction: f32,
) -> Frame {
let c0 = current;
let c1 = (next_1 - previous) * 0.5;
let c2 = previous - current * 2.5 + next_1 * 2.0 - next_2 * 0.5;
let c3 = (next_2 - previous) * 0.5 + (current - next_1) * 1.5;
((c3 * fraction + c2) * fraction + c1) * fraction + c0
}