subsonic-tui/vendor/github.com/gopxl/beep/resample.go

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package beep
import (
"fmt"
"math"
)
// Resample takes a Streamer which is assumed to stream at the old sample rate and returns a
// Streamer, which streams the data from the original Streamer resampled to the new sample rate.
//
// This is, for example, useful when mixing multiple Streamer with different sample rates, either
// through a beep.Mixer, or through a speaker. Speaker has a constant sample rate. Thus, playing
// Streamer which stream at a different sample rate will lead to a changed speed and pitch of the
// playback.
//
// sr := beep.SampleRate(48000)
// speaker.Init(sr, sr.N(time.Second/2))
// speaker.Play(beep.Resample(3, format.SampleRate, sr, s))
//
// In the example, the original sample rate of the source if format.SampleRate. We want to play it
// at the speaker's native sample rate and thus we need to resample.
//
// The quality argument specifies the quality of the resampling process. Higher quality implies
// worse performance. Values below 1 or above 64 are invalid and Resample will panic. Here's a table
// for deciding which quality to pick.
//
// quality | use case
// --------|---------
// 1 | very high performance, on-the-fly resampling, low quality
// 3-4 | good performance, on-the-fly resampling, good quality
// 6 | higher CPU usage, usually not suitable for on-the-fly resampling, very good quality
// >6 | even higher CPU usage, for offline resampling, very good quality
//
// Sane quality values are usually below 16. Higher values will consume too much CPU, giving
// negligible quality improvements.
//
// Resample propagates errors from s.
func Resample(quality int, old, new SampleRate, s Streamer) *Resampler {
return ResampleRatio(quality, float64(old)/float64(new), s)
}
// ResampleRatio is same as Resample, except it takes the ratio of the old and the new sample rate,
// specifically, the old sample rate divided by the new sample rate. Aside from correcting the
// sample rate, this can be used to change the speed of the audio. For example, resampling at the
// ratio of 2 and playing at the original sample rate will cause doubled speed in playback.
func ResampleRatio(quality int, ratio float64, s Streamer) *Resampler {
if quality < 1 || 64 < quality {
panic(fmt.Errorf("resample: invalid quality: %d", quality))
}
if math.IsInf(ratio, 0) || math.IsNaN(ratio) {
panic(fmt.Errorf("resample: invalid ratio: %f", ratio))
}
return &Resampler{
s: s,
ratio: ratio,
first: true,
buf1: make([][2]float64, 512),
buf2: make([][2]float64, 512),
pts: make([]point, quality*2),
off: 0,
pos: 0,
}
}
// Resampler is a Streamer created by Resample and ResampleRatio functions. It allows dynamic
// changing of the resampling ratio, which can be useful for dynamically changing the speed of
// streaming.
type Resampler struct {
s Streamer // the orignal streamer
ratio float64 // old sample rate / new sample rate
first bool // true when Stream was not called before
buf1, buf2 [][2]float64 // buf1 contains previous buf2, new data goes into buf2, buf1 is because interpolation might require old samples
pts []point // pts is for points used for interpolation
off int // off is the position of the start of buf2 in the original data
pos int // pos is the current position in the resampled data
}
// Stream streams the original audio resampled according to the current ratio.
func (r *Resampler) Stream(samples [][2]float64) (n int, ok bool) {
// if it's the first time, we need to fill buf2 with initial data, buf1 remains zeroed
if r.first {
sn, _ := r.s.Stream(r.buf2)
r.buf2 = r.buf2[:sn]
r.first = false
}
// we start resampling, sample by sample
for len(samples) > 0 {
again:
for c := range samples[0] {
// calculate the current position in the original data
j := float64(r.pos) * r.ratio
// find quality*2 closest samples to j and translate them to points for interpolation
for pi := range r.pts {
// calculate the index of one of the closest samples
k := int(j) + pi - len(r.pts)/2 + 1
var y float64
switch {
// the sample is in buf1
case k < r.off:
y = r.buf1[len(r.buf1)+k-r.off][c]
// the sample is in buf2
case k < r.off+len(r.buf2):
y = r.buf2[k-r.off][c]
// the sample is beyond buf2, so we need to load new data
case k >= r.off+len(r.buf2):
// we load into buf1
sn, _ := r.s.Stream(r.buf1)
// this condition happens when the original Streamer got
// drained and j is after the end of the
// original data
if int(j) >= r.off+len(r.buf2)+sn {
return n, n > 0
}
// this condition happens when the original Streamer got
// drained and this one of the closest samples is after the
// end of the original data
if k >= r.off+len(r.buf2)+sn {
y = 0
break
}
// otherwise everything is fine, we swap buffers and start
// calculating the sample again
r.off += len(r.buf2)
r.buf1 = r.buf1[:sn]
r.buf1, r.buf2 = r.buf2, r.buf1
goto again
}
r.pts[pi] = point{float64(k), y}
}
// calculate the resampled sample using polynomial interpolation from the
// quality*2 closest samples
samples[0][c] = lagrange(r.pts, j)
}
samples = samples[1:]
n++
r.pos++
}
return n, true
}
// Err propagates the original Streamer's errors.
func (r *Resampler) Err() error {
return r.s.Err()
}
// Ratio returns the current resampling ratio.
func (r *Resampler) Ratio() float64 {
return r.ratio
}
// SetRatio sets the resampling ratio. This does not cause any glitches in the stream.
func (r *Resampler) SetRatio(ratio float64) {
if math.IsInf(ratio, 0) || math.IsNaN(ratio) {
panic(fmt.Errorf("resample: invalid ratio: %f", ratio))
}
r.pos = int(float64(r.pos) * r.ratio / ratio)
r.ratio = ratio
}
// lagrange calculates the value at x of a polynomial of order len(pts)+1 which goes through all
// points in pts
func lagrange(pts []point, x float64) (y float64) {
y = 0.0
for j := range pts {
l := 1.0
for m := range pts {
if j == m {
continue
}
l *= (x - pts[m].X) / (pts[j].X - pts[m].X)
}
y += pts[j].Y * l
}
return y
}
type point struct {
X, Y float64
}