subsonic-tui/vendor/github.com/hajimehoshi/go-mp3/decode.go
Sagi Dayan 26e526f07e
initial commit
Signed-off-by: Sagi Dayan <sagidayan@gmail.com>
2024-02-20 19:10:14 +02:00

231 lines
5.2 KiB
Go

// Copyright 2017 Hajime Hoshi
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package mp3
import (
"errors"
"io"
"github.com/hajimehoshi/go-mp3/internal/consts"
"github.com/hajimehoshi/go-mp3/internal/frame"
"github.com/hajimehoshi/go-mp3/internal/frameheader"
)
// A Decoder is a MP3-decoded stream.
//
// Decoder decodes its underlying source on the fly.
type Decoder struct {
source *source
sampleRate int
length int64
frameStarts []int64
buf []byte
frame *frame.Frame
pos int64
bytesPerFrame int64
}
func (d *Decoder) readFrame() error {
var err error
d.frame, _, err = frame.Read(d.source, d.source.pos, d.frame)
if err != nil {
if err == io.EOF {
return io.EOF
}
if _, ok := err.(*consts.UnexpectedEOF); ok {
// TODO: Log here?
return io.EOF
}
return err
}
d.buf = append(d.buf, d.frame.Decode()...)
return nil
}
// Read is io.Reader's Read.
func (d *Decoder) Read(buf []byte) (int, error) {
for len(d.buf) == 0 {
if err := d.readFrame(); err != nil {
return 0, err
}
}
n := copy(buf, d.buf)
d.buf = d.buf[n:]
d.pos += int64(n)
return n, nil
}
// Seek is io.Seeker's Seek.
//
// Seek returns an error when the underlying source is not io.Seeker.
//
// Note that seek uses a byte offset but samples are aligned to 4 bytes (2
// channels, 2 bytes each). Be careful to seek to an offset that is divisible by
// 4 if you want to read at full sample boundaries.
func (d *Decoder) Seek(offset int64, whence int) (int64, error) {
if offset == 0 && whence == io.SeekCurrent {
// Handle the special case of asking for the current position specially.
return d.pos, nil
}
npos := int64(0)
switch whence {
case io.SeekStart:
npos = offset
case io.SeekCurrent:
npos = d.pos + offset
case io.SeekEnd:
npos = d.Length() + offset
default:
return 0, errors.New("mp3: invalid whence")
}
d.pos = npos
d.buf = nil
d.frame = nil
f := d.pos / d.bytesPerFrame
// If the frame is not first, read the previous ahead of reading that
// because the previous frame can affect the targeted frame.
if f > 0 {
f--
if _, err := d.source.Seek(d.frameStarts[f], 0); err != nil {
return 0, err
}
if err := d.readFrame(); err != nil {
return 0, err
}
if err := d.readFrame(); err != nil {
return 0, err
}
d.buf = d.buf[d.bytesPerFrame+(d.pos%d.bytesPerFrame):]
} else {
if _, err := d.source.Seek(d.frameStarts[f], 0); err != nil {
return 0, err
}
if err := d.readFrame(); err != nil {
return 0, err
}
d.buf = d.buf[d.pos:]
}
return npos, nil
}
// SampleRate returns the sample rate like 44100.
//
// Note that the sample rate is retrieved from the first frame.
func (d *Decoder) SampleRate() int {
return d.sampleRate
}
func (d *Decoder) ensureFrameStartsAndLength() error {
if d.length != invalidLength {
return nil
}
if _, ok := d.source.reader.(io.Seeker); !ok {
return nil
}
// Keep the current position.
pos, err := d.source.Seek(0, io.SeekCurrent)
if err != nil {
return err
}
if err := d.source.rewind(); err != nil {
return err
}
if err := d.source.skipTags(); err != nil {
return err
}
l := int64(0)
for {
h, pos, err := frameheader.Read(d.source, d.source.pos)
if err != nil {
if err == io.EOF {
break
}
if _, ok := err.(*consts.UnexpectedEOF); ok {
// TODO: Log here?
break
}
return err
}
d.frameStarts = append(d.frameStarts, pos)
d.bytesPerFrame = int64(h.BytesPerFrame())
l += d.bytesPerFrame
framesize, err := h.FrameSize()
if err != nil {
return err
}
buf := make([]byte, framesize-4)
if _, err := d.source.ReadFull(buf); err != nil {
if err == io.EOF {
break
}
return err
}
}
d.length = l
if _, err := d.source.Seek(pos, io.SeekStart); err != nil {
return err
}
return nil
}
const invalidLength = -1
// Length returns the total size in bytes.
//
// Length returns -1 when the total size is not available
// e.g. when the given source is not io.Seeker.
func (d *Decoder) Length() int64 {
return d.length
}
// NewDecoder decodes the given io.Reader and returns a decoded stream.
//
// The stream is always formatted as 16bit (little endian) 2 channels
// even if the source is single channel MP3.
// Thus, a sample always consists of 4 bytes.
func NewDecoder(r io.Reader) (*Decoder, error) {
s := &source{
reader: r,
}
d := &Decoder{
source: s,
length: invalidLength,
}
if err := s.skipTags(); err != nil {
return nil, err
}
// TODO: Is readFrame here really needed?
if err := d.readFrame(); err != nil {
return nil, err
}
freq, err := d.frame.SamplingFrequency()
if err != nil {
return nil, err
}
d.sampleRate = freq
if err := d.ensureFrameStartsAndLength(); err != nil {
return nil, err
}
return d, nil
}