av/stream/flac/decode.go

143 lines
3.9 KiB
Go

/*
NAME
decode.go
DESCRIPTION
decode.go provides functionality for the decoding of FLAC compressed audio
AUTHOR
Saxon Nelson-Milton <saxon@ausocean.org>
LICENSE
decode.go is Copyright (C) 2017-2019 the Australian Ocean Lab (AusOcean)
It is free software: you can redistribute it and/or modify them
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
It is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
*/
package flac
import (
"bytes"
"errors"
"io"
"github.com/go-audio/audio"
"github.com/go-audio/wav"
"github.com/mewkiz/flac"
)
const wavFormat = 1
// writeSeeker implements a memory based io.WriteSeeker.
type writeSeeker struct {
buf []byte
pos int
}
// Bytes returns the bytes contained in the writeSeekers buffer.
func (ws *writeSeeker) Bytes() []byte {
return ws.buf
}
// Write writes len(p) bytes from p to the writeSeeker's buf and returns the number
// of bytes written. If less than len(p) bytes are written, an error is returned.
func (ws *writeSeeker) Write(p []byte) (n int, err error) {
minCap := ws.pos + len(p)
if minCap > cap(ws.buf) { // Make sure buf has enough capacity:
buf2 := make([]byte, len(ws.buf), minCap+len(p)) // add some extra
copy(buf2, ws.buf)
ws.buf = buf2
}
if minCap > len(ws.buf) {
ws.buf = ws.buf[:minCap]
}
copy(ws.buf[ws.pos:], p)
ws.pos += len(p)
return len(p), nil
}
// Seek sets the offset for the next Read or Write to offset, interpreted according
// to whence: SeekStart means relative to the start of the file, SeekCurrent means
// relative to the current offset, and SeekEnd means relative to the end. Seek returns
// the new offset relative to the start of the file and an error, if any.
func (ws *writeSeeker) Seek(offset int64, whence int) (int64, error) {
newPos, offs := 0, int(offset)
switch whence {
case io.SeekStart:
newPos = offs
case io.SeekCurrent:
newPos = ws.pos + offs
case io.SeekEnd:
newPos = len(ws.buf) + offs
}
if newPos < 0 {
return 0, errors.New("negative result pos")
}
ws.pos = newPos
return int64(newPos), nil
}
// Decode takes buf, a slice of FLAC, and decodes to WAV. If complete decoding
// fails, an error is returned.
func Decode(buf []byte) ([]byte, error) {
// Lex the FLAC into a stream to hold audio and it's properties.
r := bytes.NewReader(buf)
stream, err := flac.Parse(r)
if err != nil {
return nil, errors.New("Could not parse FLAC")
}
// Create WAV encoder and pass writeSeeker that will store output WAV.
ws := &writeSeeker{}
sr := int(stream.Info.SampleRate)
bps := int(stream.Info.BitsPerSample)
nc := int(stream.Info.NChannels)
enc := wav.NewEncoder(ws, sr, bps, nc, wavFormat)
defer enc.Close()
// Decode FLAC into frames of samples
intBuf := &audio.IntBuffer{
Format: &audio.Format{NumChannels: nc, SampleRate: sr},
SourceBitDepth: bps,
}
return decodeFrames(stream, intBuf, enc, ws)
}
//
func decodeFrames(s *flac.Stream, intBuf *audio.IntBuffer, e *wav.Encoder, ws *writeSeeker) ([]byte, error) {
var data []int
for {
frame, err := s.ParseNext()
// If we've reached the end of the stream then we can output the writeSeeker's buffer.
if err == io.EOF {
return ws.Bytes(), nil
} else if err != nil {
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]))
}
}
intBuf.Data = data
if err := e.Write(intBuf); err != nil {
return nil, err
}
}
}