ebiten/audio/mp3/decode_notjs.go

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// Copyright 2017 The Ebiten Authors
//
// 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.
// +build !js
package mp3
import (
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"errors"
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"io"
)
var (
reader io.Reader
readerCache []uint8
readerPos int
readerEOF bool
)
func (f *frame) numberOfChannels() int {
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if f.header.mode == mpeg1ModeSingleChannel {
return 1
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}
return 2
}
func (f *frame) decodeL3() []uint8 {
out := make([]uint8, 576*4*2)
nch := f.numberOfChannels()
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for gr := 0; gr < 2; gr++ {
for ch := 0; ch < nch; ch++ {
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f.l3Requantize(gr, ch)
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// Reorder short blocks
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f.l3Reorder(gr, ch)
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}
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f.l3Stereo(gr)
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for ch := 0; ch < nch; ch++ {
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f.l3Antialias(gr, ch)
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// (IMDCT,windowing,overlapp add)
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f.l3HybridSynthesis(gr, ch)
f.l3FrequencyInversion(gr, ch)
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// Polyphase subband synthesis
f.l3SubbandSynthesis(gr, ch, out[576*4*gr:])
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}
}
return out
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}
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func getByte() (uint8, error) {
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for len(readerCache) == 0 && !readerEOF {
buf := make([]uint8, 4096)
n, err := reader.Read(buf)
readerCache = append(readerCache, buf[:n]...)
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if err != nil {
if err == io.EOF {
readerEOF = true
} else {
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return 0, err
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}
}
}
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if len(readerCache) == 0 {
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return 0, io.EOF
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}
b := readerCache[0]
readerCache = readerCache[1:]
readerPos++
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return b, nil
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}
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func getBytes(buf []int) (int, error) {
for i := range buf {
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v, err := getByte()
buf[i] = int(v)
if err == io.EOF {
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return i, io.EOF
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}
}
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return len(buf), nil
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}
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func getFilepos() int {
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return readerPos
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}
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var eof = errors.New("mp3: expected EOF")
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func decode(r io.Reader, w io.Writer) error {
reader = r
var f *frame
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for {
var err error
f, err = f.readNextFrame()
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if err == nil {
out := f.decodeL3()
if _, err := w.Write(out); err != nil {
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return err
}
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continue
}
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if err == eof {
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break
}
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return err
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}
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return nil
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}