ebiten/audio/mp3/decode_gopherjs.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
// +build !wasm
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package mp3
import (
"errors"
"fmt"
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"io"
"io/ioutil"
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"math"
"syscall/js"
"time"
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"github.com/hajimehoshi/ebiten/audio"
)
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// TODO: This just uses decodeAudioData, that can treat audio files other than MP3.
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type Stream struct {
leftData []float32
rightData []float32
posInBytes int
}
var (
errTryAgain = errors.New("audio/mp3: try again")
errTimeout = errors.New("audio/mp3: timeout")
)
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func (s *Stream) Read(b []byte) (int, error) {
l := len(s.leftData)*4 - s.posInBytes
if l > len(b) {
l = len(b)
}
l = l / 4 * 4
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const max = 1<<15 - 1
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for i := 0; i < l/4; i++ {
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il := int32(s.leftData[s.posInBytes/4+i] * max)
if il > max {
il = max
}
if il < -max {
il = -max
}
ir := int32(s.rightData[s.posInBytes/4+i] * max)
if ir > max {
ir = max
}
if ir < -max {
ir = -max
}
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b[4*i] = byte(il)
b[4*i+1] = byte(il >> 8)
b[4*i+2] = byte(ir)
b[4*i+3] = byte(ir >> 8)
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}
s.posInBytes += l
if s.posInBytes == len(s.leftData)*4 {
return l, io.EOF
}
return l, nil
}
func (s *Stream) Seek(offset int64, whence int) (int64, error) {
next := int64(0)
switch whence {
case io.SeekStart:
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next = offset
case io.SeekCurrent:
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next = int64(s.posInBytes) + offset
case io.SeekEnd:
next = s.Length() + offset
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}
s.posInBytes = int(next)
return next, nil
}
func (s *Stream) Close() error {
return nil
}
func (s *Stream) Length() int64 {
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return int64(len(s.leftData) * 4)
}
// Size is deprecated as of 1.6.0-alpha. Use Length instead.
func (s *Stream) Size() int64 {
return s.Length()
}
// seekNextFrame seeks the next frame and returns the new buffer with the new position.
// seekNextFrame also returns true when seeking is successful, or false otherwise.
//
// Seeking is necessary when decoding fails. Safari's MP3 decoder can't treat IDs well (#438).
func seekNextFrame(buf []byte) ([]byte, bool) {
// TODO: Need to skip tags explicitly? (hajimehoshi/go-mp3#9)
if len(buf) < 1 {
return nil, false
}
buf = buf[1:]
for {
if buf[0] == 0xff && buf[1]&0xfe == 0xfe {
break
}
buf = buf[1:]
if len(buf) < 2 {
return nil, false
}
}
return buf, true
}
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func Decode(context *audio.Context, src audio.ReadSeekCloser) (*Stream, error) {
b, err := ioutil.ReadAll(src)
if err != nil {
return nil, err
}
if err := src.Close(); err != nil {
return nil, err
}
var s *Stream
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try := 0
for {
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s, err = decode(context, b, try)
switch err {
case errTryAgain:
buf, ok := seekNextFrame(b)
if !ok {
return nil, fmt.Errorf("audio/mp3: Decode failed: invalid format?")
}
b = buf
continue
case errTimeout:
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try++
continue
default:
if err != nil {
return nil, err
}
}
break
}
return s, nil
}
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var offlineAudioContextClass = js.Null()
func init() {
if klass := js.Global().Get("OfflineAudioContext"); klass != js.Undefined() {
offlineAudioContextClass = klass
return
}
if klass := js.Global().Get("webkitOfflineAudioContext"); klass != js.Undefined() {
offlineAudioContextClass = klass
return
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}
}
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func float32ArrayToSlice(arr js.Value) []float32 {
f := make([]float32, arr.Length())
a := js.TypedArrayOf(f)
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a.Call("set", arr)
a.Release()
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return f
}
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func decode(context *audio.Context, buf []byte, try int) (*Stream, error) {
if offlineAudioContextClass == js.Null() {
return nil, errors.New("audio/mp3: OfflineAudioContext is not available")
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}
s := &Stream{}
ch := make(chan error)
// TODO: webkitOfflineAudioContext's constructor might causes 'Syntax' error
// when the sample rate is not so usual like 22050 on Safari.
// Should this be handled before calling this?
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// TODO: 1 is a correct second argument?
oc := offlineAudioContextClass.New(2, 1, context.SampleRate())
u8 := js.TypedArrayOf(buf)
defer u8.Release()
a := u8.Get("buffer").Call("slice", u8.Get("byteOffset"), u8.Get("byteOffset").Int()+u8.Get("byteLength").Int())
succeeded := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
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buf := args[0]
s.leftData = float32ArrayToSlice(buf.Call("getChannelData", 0))
switch n := buf.Get("numberOfChannels").Int(); n {
case 1:
s.rightData = s.leftData
close(ch)
case 2:
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s.rightData = float32ArrayToSlice(buf.Call("getChannelData", 1))
close(ch)
default:
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ch <- fmt.Errorf("audio/mp3: number of channels must be 1 or 2 but %d", n)
}
return nil
})
defer succeeded.Release()
failed := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
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err := args[0]
if err != js.Null() || err != js.Undefined() {
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ch <- fmt.Errorf("audio/mp3: decodeAudioData failed: %v", err)
} else {
// On Safari, error value might be null and it is needed to retry decoding
// from the next frame (#438).
ch <- errTryAgain
}
return nil
})
defer failed.Release()
oc.Call("decodeAudioData", a, succeeded, failed)
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timeout := time.Duration(math.Pow(2, float64(try))) * time.Second
t := time.NewTimer(timeout)
defer t.Stop()
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select {
case err := <-ch:
if err != nil {
return nil, err
}
case <-t.C:
// Sometimes decode fails without calling the callbacks (#464).
// Let's just try again in this case.
return nil, errTimeout
}
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return s, nil
}