273 lines
7.3 KiB
Go
273 lines
7.3 KiB
Go
// Copyright 2017 Hajime Hoshi
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package frameheader
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import (
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"errors"
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"fmt"
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"io"
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"github.com/hajimehoshi/go-mp3/internal/consts"
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)
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// A mepg1FrameHeader is MPEG1 Layer 1-3 frame header
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type FrameHeader uint32
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// ID returns this header's ID stored in position 20,19
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func (f FrameHeader) ID() consts.Version {
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return consts.Version((f & 0x00180000) >> 19)
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}
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// Layer returns the mpeg layer of this frame stored in position 18,17
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func (f FrameHeader) Layer() consts.Layer {
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return consts.Layer((f & 0x00060000) >> 17)
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}
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// ProtectionBit returns the protection bit stored in position 16
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func (f FrameHeader) ProtectionBit() int {
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return int(f&0x00010000) >> 16
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}
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// BirateIndex returns the bitrate index stored in position 15,12
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func (f FrameHeader) BitrateIndex() int {
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return int(f&0x0000f000) >> 12
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}
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// SamplingFrequency returns the SamplingFrequency in Hz stored in position 11,10
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func (f FrameHeader) SamplingFrequency() consts.SamplingFrequency {
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return consts.SamplingFrequency(int(f&0x00000c00) >> 10)
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}
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func (f FrameHeader) SamplingFrequencyValue() (int, error) {
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switch f.SamplingFrequency() {
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case 0:
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return 44100 >> uint(f.LowSamplingFrequency()), nil
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case 1:
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return 48000 >> uint(f.LowSamplingFrequency()), nil
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case 2:
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return 32000 >> uint(f.LowSamplingFrequency()), nil
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}
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return 0, errors.New("mp3: frame header has invalid sample frequency")
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}
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// PaddingBit returns the padding bit stored in position 9
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func (f FrameHeader) PaddingBit() int {
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return int(f&0x00000200) >> 9
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}
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// PrivateBit returns the private bit stored in position 8 - this bit may be used to store arbitrary data to be used
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// by an application
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func (f FrameHeader) PrivateBit() int {
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return int(f&0x00000100) >> 8
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}
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// Mode returns the channel mode, stored in position 7,6
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func (f FrameHeader) Mode() consts.Mode {
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return consts.Mode((f & 0x000000c0) >> 6)
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}
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// modeExtension returns the mode_extension - for use with Joint Stereo - stored in position 4,5
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func (f FrameHeader) modeExtension() int {
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return int(f&0x00000030) >> 4
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}
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// UseMSStereo returns a boolean value indicating whether the frame uses middle/side stereo.
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func (f FrameHeader) UseMSStereo() bool {
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if f.Mode() != consts.ModeJointStereo {
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return false
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}
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return f.modeExtension()&0x2 != 0
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}
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// UseIntensityStereo returns a boolean value indicating whether the frame uses intensity stereo.
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func (f FrameHeader) UseIntensityStereo() bool {
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if f.Mode() != consts.ModeJointStereo {
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return false
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}
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return f.modeExtension()&0x1 != 0
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}
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// Copyright returns whether or not this recording is copywritten - stored in position 3
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func (f FrameHeader) Copyright() int {
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return int(f&0x00000008) >> 3
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}
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// OriginalOrCopy returns whether or not this is an Original recording or a copy of one - stored in position 2
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func (f FrameHeader) OriginalOrCopy() int {
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return int(f&0x00000004) >> 2
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}
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// Emphasis returns emphasis - the emphasis indication is here to tell the decoder that the file must be de-emphasized - stored in position 0,1
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func (f FrameHeader) Emphasis() int {
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return int(f&0x00000003) >> 0
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}
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// LowSamplingFrequency returns whether the frame is encoded in a low sampling frequency => 0 = MPEG-1, 1 = MPEG-2/2.5
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func (f FrameHeader) LowSamplingFrequency() int {
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if f.ID() == consts.Version1 {
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return 0
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}
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return 1
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}
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func (f FrameHeader) BytesPerFrame() int {
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return consts.SamplesPerGr * f.Granules() * 4
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}
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func (f FrameHeader) Granules() int {
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return consts.GranulesMpeg1 >> uint(f.LowSamplingFrequency()) // MPEG2 uses only 1 granule
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}
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// IsValid returns a boolean value indicating whether the header is valid or not.
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func (f FrameHeader) IsValid() bool {
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const sync = 0xffe00000
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if (f & sync) != sync {
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return false
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}
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if f.ID() == consts.VersionReserved {
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return false
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}
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if f.BitrateIndex() == 15 {
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return false
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}
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if f.SamplingFrequency() == consts.SamplingFrequencyReserved {
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return false
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}
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if f.Layer() == consts.LayerReserved {
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return false
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}
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if f.Emphasis() == 2 {
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return false
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}
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return true
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}
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func (f FrameHeader) Bitrate() int {
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bitrates := [2][3][16]int{
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{
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// MPEG 1 Layer 3
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{0, 32000, 40000, 48000, 56000, 64000, 80000, 96000,
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112000, 128000, 160000, 192000, 224000, 256000, 320000},
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// MPEG 1 Layer 2
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{0, 32000, 48000, 56000, 64000, 80000, 96000, 112000,
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128000, 160000, 192000, 224000, 256000, 320000, 384000},
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// MPEG 1 Layer 1
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{0, 32000, 64000, 96000, 128000, 160000, 192000, 224000,
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256000, 288000, 320000, 352000, 384000, 416000, 448000},
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},
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{
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// MPEG2 2 Layer 3
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{0, 8000, 16000, 24000, 32000, 40000, 48000, 56000,
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64000, 80000, 96000, 112000, 128000, 144000, 160000},
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// MPEG 2 Layer 2
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{0, 8000, 16000, 24000, 32000, 40000, 48000, 56000,
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64000, 80000, 96000, 112000, 128000, 144000, 160000},
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// MPEG 2 Layer 1
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{0, 32000, 48000, 56000, 64000, 80000, 96000, 112000,
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128000, 144000, 160000, 176000, 192000, 224000, 256000},
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},
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}
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return bitrates[f.LowSamplingFrequency()][f.Layer()-1][f.BitrateIndex()]
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}
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func (f FrameHeader) FrameSize() (int, error) {
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freq, err := f.SamplingFrequencyValue()
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if err != nil {
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return 0, err
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}
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size := ((144*f.Bitrate())/freq +
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int(f.PaddingBit())) >> uint(f.LowSamplingFrequency())
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return size, nil
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}
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func (f FrameHeader) SideInfoSize() int {
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mono := f.Mode() == consts.ModeSingleChannel
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var sideinfo_size int
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if f.LowSamplingFrequency() == 1 {
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if mono {
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sideinfo_size = 9
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} else {
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sideinfo_size = 17
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}
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} else {
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if mono {
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sideinfo_size = 17
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} else {
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sideinfo_size = 32
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}
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}
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return sideinfo_size
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}
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func (f FrameHeader) NumberOfChannels() int {
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if f.Mode() == consts.ModeSingleChannel {
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return 1
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}
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return 2
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}
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type FullReader interface {
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ReadFull([]byte) (int, error)
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}
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func Read(source FullReader, position int64) (h FrameHeader, startPosition int64, err error) {
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buf := make([]byte, 4)
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if n, err := source.ReadFull(buf); n < 4 {
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if err == io.EOF {
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if n == 0 {
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// Expected EOF
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return 0, 0, io.EOF
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}
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return 0, 0, &consts.UnexpectedEOF{"readHeader (1)"}
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}
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return 0, 0, err
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}
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b1 := uint32(buf[0])
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b2 := uint32(buf[1])
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b3 := uint32(buf[2])
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b4 := uint32(buf[3])
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header := FrameHeader((b1 << 24) | (b2 << 16) | (b3 << 8) | (b4 << 0))
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for !header.IsValid() {
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b1 = b2
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b2 = b3
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b3 = b4
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buf := make([]byte, 1)
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if _, err := source.ReadFull(buf); err != nil {
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if err == io.EOF {
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return 0, 0, &consts.UnexpectedEOF{"readHeader (2)"}
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}
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return 0, 0, err
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}
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b4 = uint32(buf[0])
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header = FrameHeader((b1 << 24) | (b2 << 16) | (b3 << 8) | (b4 << 0))
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position++
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}
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// If we get here we've found the sync word, and can decode the header
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// which is in the low 20 bits of the 32-bit sync+header word.
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if header.BitrateIndex() == 0 {
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return 0, 0, fmt.Errorf("mp3: free bitrate format is not supported. Header word is 0x%08x at position %d",
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header, position)
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}
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return header, position, nil
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}
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