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105 lines
2.2 KiB
Go
105 lines
2.2 KiB
Go
// Package mp3 implements audio data decoding in MP3 format.
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package mp3
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import (
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"fmt"
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"io"
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"github.com/faiface/beep"
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gomp3 "github.com/hajimehoshi/go-mp3"
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"github.com/pkg/errors"
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)
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const (
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gomp3NumChannels = 2
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gomp3Precision = 2
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gomp3BytesPerFrame = gomp3NumChannels * gomp3Precision
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)
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// Decode takes a ReadCloser containing audio data in MP3 format and returns a StreamSeekCloser,
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// which streams that audio. The Seek method will panic if rc is not io.Seeker.
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//
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// Do not close the supplied ReadSeekCloser, instead, use the Close method of the returned
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// StreamSeekCloser when you want to release the resources.
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func Decode(rc io.ReadCloser) (s beep.StreamSeekCloser, format beep.Format, err error) {
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defer func() {
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if err != nil {
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err = errors.Wrap(err, "mp3")
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}
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}()
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d, err := gomp3.NewDecoder(rc)
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if err != nil {
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return nil, beep.Format{}, err
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}
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format = beep.Format{
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SampleRate: beep.SampleRate(d.SampleRate()),
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NumChannels: gomp3NumChannels,
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Precision: gomp3Precision,
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}
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return &decoder{rc, d, format, 0, nil}, format, nil
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}
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type decoder struct {
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closer io.Closer
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d *gomp3.Decoder
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f beep.Format
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pos int
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err error
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}
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func (d *decoder) Stream(samples [][2]float64) (n int, ok bool) {
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if d.err != nil {
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return 0, false
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}
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var tmp [gomp3BytesPerFrame]byte
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for i := range samples {
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dn, err := d.d.Read(tmp[:])
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if dn == len(tmp) {
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samples[i], _ = d.f.DecodeSigned(tmp[:])
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d.pos += dn
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n++
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ok = true
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}
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if err == io.EOF {
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break
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}
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if err != nil {
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d.err = errors.Wrap(err, "mp3")
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break
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}
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}
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return n, ok
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}
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func (d *decoder) Err() error {
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return d.err
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}
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func (d *decoder) Len() int {
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return int(d.d.Length()) / gomp3BytesPerFrame
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}
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func (d *decoder) Position() int {
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return d.pos / gomp3BytesPerFrame
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}
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func (d *decoder) Seek(p int) error {
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if p < 0 || d.Len() < p {
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return fmt.Errorf("mp3: seek position %v out of range [%v, %v]", p, 0, d.Len())
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}
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_, err := d.d.Seek(int64(p)*gomp3BytesPerFrame, io.SeekStart)
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if err != nil {
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return errors.Wrap(err, "mp3")
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}
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d.pos = p * gomp3BytesPerFrame
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return nil
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}
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func (d *decoder) Close() error {
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err := d.closer.Close()
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if err != nil {
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return errors.Wrap(err, "mp3")
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}
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return nil
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}
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