263 lines
6.8 KiB
Go
263 lines
6.8 KiB
Go
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package beep
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import (
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"fmt"
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"math"
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"time"
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)
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// SampleRate is the number of samples per second.
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type SampleRate int
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// D returns the duration of n samples.
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func (sr SampleRate) D(n int) time.Duration {
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return time.Second * time.Duration(n) / time.Duration(sr)
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}
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// N returns the number of samples that last for d duration.
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func (sr SampleRate) N(d time.Duration) int {
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return int(d * time.Duration(sr) / time.Second)
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}
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// Format is the format of a Buffer or another audio source.
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type Format struct {
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// SampleRate is the number of samples per second.
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SampleRate SampleRate
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// NumChannels is the number of channels. The value of 1 is mono, the value of 2 is stereo.
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// The samples should always be interleaved.
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NumChannels int
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// Precision is the number of bytes used to encode a single sample. Only values up to 6 work
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// well, higher values loose precision due to floating point numbers.
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Precision int
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}
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// Width returns the number of bytes per one frame (samples in all channels).
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//
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// This is equal to f.NumChannels * f.Precision.
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func (f Format) Width() int {
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return f.NumChannels * f.Precision
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}
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// EncodeSigned encodes a single sample in f.Width() bytes to p in signed format.
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func (f Format) EncodeSigned(p []byte, sample [2]float64) (n int) {
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return f.encode(true, p, sample)
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}
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// EncodeUnsigned encodes a single sample in f.Width() bytes to p in unsigned format.
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func (f Format) EncodeUnsigned(p []byte, sample [2]float64) (n int) {
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return f.encode(false, p, sample)
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}
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// DecodeSigned decodes a single sample encoded in f.Width() bytes from p in signed format.
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func (f Format) DecodeSigned(p []byte) (sample [2]float64, n int) {
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return f.decode(true, p)
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}
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// DecodeUnsigned decodes a single sample encoded in f.Width() bytes from p in unsigned format.
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func (f Format) DecodeUnsigned(p []byte) (sample [2]float64, n int) {
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return f.decode(false, p)
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}
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func (f Format) encode(signed bool, p []byte, sample [2]float64) (n int) {
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switch {
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case f.NumChannels == 1:
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x := norm((sample[0] + sample[1]) / 2)
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p = p[encodeFloat(signed, f.Precision, p, x):]
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case f.NumChannels >= 2:
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for c := range sample {
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x := norm(sample[c])
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p = p[encodeFloat(signed, f.Precision, p, x):]
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}
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for c := len(sample); c < f.NumChannels; c++ {
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p = p[encodeFloat(signed, f.Precision, p, 0):]
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}
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default:
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panic(fmt.Errorf("format: encode: invalid number of channels: %d", f.NumChannels))
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}
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return f.Width()
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}
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func (f Format) decode(signed bool, p []byte) (sample [2]float64, n int) {
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switch {
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case f.NumChannels == 1:
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x, _ := decodeFloat(signed, f.Precision, p)
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return [2]float64{x, x}, f.Width()
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case f.NumChannels >= 2:
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for c := range sample {
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x, n := decodeFloat(signed, f.Precision, p)
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sample[c] = x
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p = p[n:]
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}
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for c := len(sample); c < f.NumChannels; c++ {
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_, n := decodeFloat(signed, f.Precision, p)
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p = p[n:]
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}
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return sample, f.Width()
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default:
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panic(fmt.Errorf("format: decode: invalid number of channels: %d", f.NumChannels))
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}
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}
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func encodeFloat(signed bool, precision int, p []byte, x float64) (n int) {
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var xUint64 uint64
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if signed {
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xUint64 = floatToSigned(precision, x)
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} else {
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xUint64 = floatToUnsigned(precision, x)
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}
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for i := 0; i < precision; i++ {
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p[i] = byte(xUint64)
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xUint64 >>= 8
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}
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return precision
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}
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func decodeFloat(signed bool, precision int, p []byte) (x float64, n int) {
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var xUint64 uint64
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for i := precision - 1; i >= 0; i-- {
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xUint64 <<= 8
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xUint64 += uint64(p[i])
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}
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if signed {
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return signedToFloat(precision, xUint64), precision
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}
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return unsignedToFloat(precision, xUint64), precision
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}
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func floatToSigned(precision int, x float64) uint64 {
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if x < 0 {
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compl := uint64(-x * (math.Exp2(float64(precision)*8-1) - 1))
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return uint64(1<<uint(precision*8)) - compl
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}
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return uint64(x * (math.Exp2(float64(precision)*8-1) - 1))
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}
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func floatToUnsigned(precision int, x float64) uint64 {
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return uint64((x + 1) / 2 * (math.Exp2(float64(precision)*8) - 1))
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}
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func signedToFloat(precision int, xUint64 uint64) float64 {
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if xUint64 >= 1<<uint(precision*8-1) {
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compl := 1<<uint(precision*8) - xUint64
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return -float64(int64(compl)) / (math.Exp2(float64(precision)*8-1) - 1)
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}
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return float64(int64(xUint64)) / (math.Exp2(float64(precision)*8-1) - 1)
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}
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func unsignedToFloat(precision int, xUint64 uint64) float64 {
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return float64(xUint64)/(math.Exp2(float64(precision)*8)-1)*2 - 1
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}
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func norm(x float64) float64 {
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if x < -1 {
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return -1
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}
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if x > +1 {
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return +1
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}
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return x
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}
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// Buffer is a storage for audio data. You can think of it as a bytes.Buffer for audio samples.
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type Buffer struct {
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f Format
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data []byte
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tmp []byte
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}
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// NewBuffer creates a new empty Buffer which stores samples in the provided format.
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func NewBuffer(f Format) *Buffer {
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return &Buffer{f: f, tmp: make([]byte, f.Width())}
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}
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// Format returns the format of the Buffer.
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func (b *Buffer) Format() Format {
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return b.f
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}
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// Len returns the number of samples currently in the Buffer.
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func (b *Buffer) Len() int {
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return len(b.data) / b.f.Width()
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}
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// Pop removes n samples from the beginning of the Buffer.
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//
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// Existing Streamers are not affected.
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func (b *Buffer) Pop(n int) {
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b.data = b.data[n*b.f.Width():]
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}
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// Append adds all audio data from the given Streamer to the end of the Buffer.
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//
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// The Streamer will be drained when this method finishes.
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func (b *Buffer) Append(s Streamer) {
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var samples [512][2]float64
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for {
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n, ok := s.Stream(samples[:])
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if !ok {
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break
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}
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for _, sample := range samples[:n] {
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b.f.EncodeSigned(b.tmp, sample)
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b.data = append(b.data, b.tmp...)
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}
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}
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}
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// Streamer returns a StreamSeeker which streams samples in the given interval (including from,
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// excluding to). If from<0 or to>b.Len() or to<from, this method panics.
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//
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// When using multiple goroutines, synchronization of Streamers with the Buffer is not required,
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// as Buffer is persistent (but efficient and garbage collected).
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func (b *Buffer) Streamer(from, to int) StreamSeeker {
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return &bufferStreamer{
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f: b.f,
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data: b.data[from*b.f.Width() : to*b.f.Width()],
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pos: 0,
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}
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}
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type bufferStreamer struct {
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f Format
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data []byte
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pos int
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}
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func (bs *bufferStreamer) Stream(samples [][2]float64) (n int, ok bool) {
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if bs.pos >= len(bs.data) {
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return 0, false
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}
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for i := range samples {
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if bs.pos >= len(bs.data) {
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break
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}
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sample, advance := bs.f.DecodeSigned(bs.data[bs.pos:])
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samples[i] = sample
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bs.pos += advance
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n++
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}
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return n, true
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}
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func (bs *bufferStreamer) Err() error {
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return nil
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}
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func (bs *bufferStreamer) Len() int {
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return len(bs.data) / bs.f.Width()
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}
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func (bs *bufferStreamer) Position() int {
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return bs.pos / bs.f.Width()
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}
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func (bs *bufferStreamer) Seek(p int) error {
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if p < 0 || bs.Len() < p {
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return fmt.Errorf("buffer: seek position %v out of range [%v, %v]", p, 0, bs.Len())
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}
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bs.pos = p * bs.f.Width()
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return nil
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}
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