av/stream/flac/decode.go

package flac

import (
	"bytes"
	"errors"
	"io"
	"io/ioutil"

	"github.com/go-audio/audio"
	"github.com/go-audio/wav"
	"github.com/mewkiz/flac"
	"github.com/orcaman/writerseeker"
)

const wavAudioFormat = 1

// Decode takes a slice of flac and decodes to wav
func Decode(buf []byte) ([]byte, error) {
	r := bytes.NewReader(buf)
	stream, err := flac.Parse(r)
	if err != nil {
		return nil, errors.New("Could not parse FLAC")
	}
	ws := &writerseeker.WriterSeeker{}
	enc := wav.NewEncoder(ws, int(stream.Info.SampleRate), int(stream.Info.BitsPerSample), int(stream.Info.NChannels), wavAudioFormat)
	defer enc.Close()
	var data []int
	var out []byte
	var d []byte
	for {
		// Decode FLAC audio samples.
		frame, err := stream.ParseNext()
		if err != nil {
			if err == io.EOF {
				break
			}
			return nil, err
		}

		// Encode WAV audio samples.
		data = data[:0]
		for i := 0; i < frame.Subframes[0].NSamples; i++ {
			for _, subframe := range frame.Subframes {
				data = append(data, int(subframe.Samples[i]))
			}
		}
		buf := &audio.IntBuffer{
			Format: &audio.Format{
				NumChannels: int(stream.Info.NChannels),
				SampleRate:  int(stream.Info.SampleRate),
			},
			Data:           data,
			SourceBitDepth: int(stream.Info.BitsPerSample),
		}
		if err := enc.Write(buf); err != nil {
			return nil, err
		}
		d, err = ioutil.ReadAll(ws.Reader())
		if err != nil {
			return nil, err
		}
		out = append(out, d...)
	}

	return d, nil
}