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143 lines
4.3 KiB
Go
143 lines
4.3 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 sideinfo
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import (
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"fmt"
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"io"
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"github.com/hajimehoshi/go-mp3/internal/bits"
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"github.com/hajimehoshi/go-mp3/internal/consts"
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"github.com/hajimehoshi/go-mp3/internal/frameheader"
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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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// A SideInfo is MPEG1 Layer 3 Side Information.
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// [2][2] means [gr][ch].
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type SideInfo struct {
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MainDataBegin int // 9 bits
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PrivateBits int // 3 bits in mono, 5 in stereo
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Scfsi [2][4]int // 1 bit
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Part2_3Length [2][2]int // 12 bits
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BigValues [2][2]int // 9 bits
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GlobalGain [2][2]int // 8 bits
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ScalefacCompress [2][2]int // 4 bits
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WinSwitchFlag [2][2]int // 1 bit
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BlockType [2][2]int // 2 bits
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MixedBlockFlag [2][2]int // 1 bit
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TableSelect [2][2][3]int // 5 bits
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SubblockGain [2][2][3]int // 3 bits
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Region0Count [2][2]int // 4 bits
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Region1Count [2][2]int // 3 bits
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Preflag [2][2]int // 1 bit
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ScalefacScale [2][2]int // 1 bit
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Count1TableSelect [2][2]int // 1 bit
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Count1 [2][2]int // Not in file, calc by huffman decoder
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}
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func Read(source FullReader, header frameheader.FrameHeader) (*SideInfo, error) {
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nch := header.NumberOfChannels()
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// Calculate header audio data size
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framesize := header.FrameSize()
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if framesize > 2000 {
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return nil, fmt.Errorf("mp3: framesize = %d\n", framesize)
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}
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// Sideinfo is 17 bytes for one channel and 32 bytes for two
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sideinfo_size := 32
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if nch == 1 {
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sideinfo_size = 17
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}
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// Main data size is the rest of the frame,including ancillary data
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main_data_size := framesize - sideinfo_size - 4 // sync+header
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// CRC is 2 bytes
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if header.ProtectionBit() == 0 {
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main_data_size -= 2
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}
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// Read sideinfo from bitstream into buffer used by Bits()
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buf := make([]byte, sideinfo_size)
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n, err := source.ReadFull(buf)
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if n < sideinfo_size {
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if err == io.EOF {
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return nil, &consts.UnexpectedEOF{"sideinfo.Read"}
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}
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return nil, fmt.Errorf("mp3: couldn't read sideinfo %d bytes: %v", sideinfo_size, err)
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}
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s := bits.New(buf)
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// Parse audio data
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// Pointer to where we should start reading main data
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si := &SideInfo{}
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si.MainDataBegin = s.Bits(9)
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// Get private bits. Not used for anything.
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if header.Mode() == consts.ModeSingleChannel {
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si.PrivateBits = s.Bits(5)
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} else {
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si.PrivateBits = s.Bits(3)
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}
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// Get scale factor selection information
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for ch := 0; ch < nch; ch++ {
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for scfsi_band := 0; scfsi_band < 4; scfsi_band++ {
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si.Scfsi[ch][scfsi_band] = s.Bits(1)
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}
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}
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// Get the rest of the side information
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for gr := 0; gr < 2; gr++ {
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for ch := 0; ch < nch; ch++ {
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si.Part2_3Length[gr][ch] = s.Bits(12)
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si.BigValues[gr][ch] = s.Bits(9)
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si.GlobalGain[gr][ch] = s.Bits(8)
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si.ScalefacCompress[gr][ch] = s.Bits(4)
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si.WinSwitchFlag[gr][ch] = s.Bits(1)
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if si.WinSwitchFlag[gr][ch] == 1 {
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si.BlockType[gr][ch] = s.Bits(2)
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si.MixedBlockFlag[gr][ch] = s.Bits(1)
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for region := 0; region < 2; region++ {
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si.TableSelect[gr][ch][region] = s.Bits(5)
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}
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for window := 0; window < 3; window++ {
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si.SubblockGain[gr][ch][window] = s.Bits(3)
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}
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// TODO: This is not listed on the spec. Is this correct??
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if si.BlockType[gr][ch] == 2 && si.MixedBlockFlag[gr][ch] == 0 {
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si.Region0Count[gr][ch] = 8 // Implicit
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} else {
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si.Region0Count[gr][ch] = 7 // Implicit
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}
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// The standard is wrong on this!!!
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// Implicit
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si.Region1Count[gr][ch] = 20 - si.Region0Count[gr][ch]
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} else {
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for region := 0; region < 3; region++ {
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si.TableSelect[gr][ch][region] = s.Bits(5)
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}
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si.Region0Count[gr][ch] = s.Bits(4)
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si.Region1Count[gr][ch] = s.Bits(3)
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si.BlockType[gr][ch] = 0 // Implicit
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}
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si.Preflag[gr][ch] = s.Bits(1)
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si.ScalefacScale[gr][ch] = s.Bits(1)
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si.Count1TableSelect[gr][ch] = s.Bits(1)
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}
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}
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return si, nil
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}
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