forked from faiface/beep
/
decode.go
147 lines (136 loc) · 3.76 KB
/
decode.go
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package flac
import (
"fmt"
"io"
"github.com/faiface/beep"
"github.com/mewkiz/flac"
"github.com/pkg/errors"
)
// Decode takes a ReadCloser containing audio data in FLAC format and returns a StreamSeekCloser,
// which streams that audio. The Seek method will panic if rc is not io.Seeker.
//
// Do not close the supplied ReadSeekCloser, instead, use the Close method of the returned
// StreamSeekCloser when you want to release the resources.
func Decode(rc io.ReadCloser) (s beep.StreamSeekCloser, format beep.Format, err error) {
d := decoder{rc: rc}
defer func() { // hacky way to always close rc if an error occured
if err != nil {
d.rc.Close()
}
}()
d.stream, err = flac.New(rc)
if err != nil {
return nil, beep.Format{}, errors.Wrap(err, "flac")
}
format = beep.Format{
SampleRate: beep.SampleRate(d.stream.Info.SampleRate),
NumChannels: int(d.stream.Info.NChannels),
Precision: int(d.stream.Info.BitsPerSample / 8),
}
return &d, format, nil
}
type decoder struct {
rc io.ReadCloser
stream *flac.Stream
buf [][2]float64
pos int
err error
}
func (d *decoder) Stream(samples [][2]float64) (n int, ok bool) {
if d.err != nil {
return 0, false
}
// Copy samples from buffer.
j := 0
for i := range samples {
if j >= len(d.buf) {
// refill buffer.
if err := d.refill(); err != nil {
d.err = err
d.pos += n
return n, n > 0
}
j = 0
}
samples[i] = d.buf[j]
j++
n++
}
d.buf = d.buf[j:]
d.pos += n
return n, true
}
// refill decodes audio samples to fill the decode buffer.
func (d *decoder) refill() error {
// Empty buffer.
d.buf = d.buf[:0]
// Parse audio frame.
frame, err := d.stream.ParseNext()
if err != nil {
return err
}
// Expand buffer size if needed.
n := len(frame.Subframes[0].Samples)
if cap(d.buf) < n {
d.buf = make([][2]float64, n)
} else {
d.buf = d.buf[:n]
}
// Decode audio samples.
bps := d.stream.Info.BitsPerSample
nchannels := d.stream.Info.NChannels
switch {
case bps == 8 && nchannels == 1:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int8(frame.Subframes[0].Samples[i])) / (1<<7 - 1)
d.buf[i][1] = float64(int8(frame.Subframes[0].Samples[i])) / (1<<7 - 1)
}
case bps == 16 && nchannels == 1:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int16(frame.Subframes[0].Samples[i])) / (1<<15 - 1)
d.buf[i][1] = float64(int16(frame.Subframes[0].Samples[i])) / (1<<15 - 1)
}
case bps == 24 && nchannels == 1:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int32(frame.Subframes[0].Samples[i])) / (1<<23 - 1)
d.buf[i][1] = float64(int32(frame.Subframes[0].Samples[i])) / (1<<23 - 1)
}
case bps == 8 && nchannels >= 2:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int8(frame.Subframes[0].Samples[i])) / (1<<7 - 1)
d.buf[i][1] = float64(int8(frame.Subframes[1].Samples[i])) / (1<<7 - 1)
}
case bps == 16 && nchannels >= 2:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int16(frame.Subframes[0].Samples[i])) / (1<<15 - 1)
d.buf[i][1] = float64(int16(frame.Subframes[1].Samples[i])) / (1<<15 - 1)
}
case bps == 24 && nchannels >= 2:
for i := 0; i < n; i++ {
d.buf[i][0] = float64(int32(frame.Subframes[0].Samples[i])) / (1<<23 - 1)
d.buf[i][1] = float64(int32(frame.Subframes[1].Samples[i])) / (1<<23 - 1)
}
default:
panic(fmt.Errorf("support for %d bits-per-sample and %d channels combination not yet implemented", bps, nchannels))
}
return nil
}
func (d *decoder) Err() error {
return d.err
}
func (d *decoder) Len() int {
return int(d.stream.Info.NSamples)
}
func (d *decoder) Position() int {
return d.pos
}
func (d *decoder) Seek(p int) error {
return errors.New("flac.decoder.Seek: not yet implemented")
}
func (d *decoder) Close() error {
err := d.rc.Close()
if err != nil {
return errors.Wrap(err, "flac")
}
return nil
}