subsonic-tui/vendor/github.com/hajimehoshi/go-mp3/internal/sideinfo/sideinfo.go
Sagi Dayan 48661005be
initial commit
Signed-off-by: Sagi Dayan <sagidayan@gmail.com>
2024-09-01 16:30:56 +03:00

161 lines
4.7 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 sideinfo
import (
"fmt"
"io"
"github.com/hajimehoshi/go-mp3/internal/bits"
"github.com/hajimehoshi/go-mp3/internal/consts"
"github.com/hajimehoshi/go-mp3/internal/frameheader"
)
type FullReader interface {
ReadFull([]byte) (int, error)
}
// A SideInfo is MPEG1 Layer 3 Side Information.
// [2][2] means [gr][ch].
type SideInfo struct {
MainDataBegin int // 9 bits
PrivateBits int // 3 bits in mono, 5 in stereo
Scfsi [2][4]int // 1 bit
Part2_3Length [2][2]int // 12 bits
BigValues [2][2]int // 9 bits
GlobalGain [2][2]int // 8 bits
ScalefacCompress [2][2]int // 4 bits
WinSwitchFlag [2][2]int // 1 bit
BlockType [2][2]int // 2 bits
MixedBlockFlag [2][2]int // 1 bit
TableSelect [2][2][3]int // 5 bits
SubblockGain [2][2][3]int // 3 bits
Region0Count [2][2]int // 4 bits
Region1Count [2][2]int // 3 bits
Preflag [2][2]int // 1 bit
ScalefacScale [2][2]int // 1 bit
Count1TableSelect [2][2]int // 1 bit
Count1 [2][2]int // Not in file, calc by huffman decoder
}
var sideInfoBitsToRead = [2][4]int{
{ // MPEG 1
9, 5, 3, 4,
},
{ // MPEG 2
8, 1, 2, 9,
},
}
func Read(source FullReader, header frameheader.FrameHeader) (*SideInfo, error) {
nch := header.NumberOfChannels()
framesize, err := header.FrameSize()
if err != nil {
return nil, err
}
if framesize > 2000 {
return nil, fmt.Errorf("mp3: framesize = %d\n", framesize)
}
sideinfo_size := header.SideInfoSize()
// Main data size is the rest of the frame,including ancillary data
main_data_size := framesize - sideinfo_size - 4 // sync+header
// CRC is 2 bytes
if header.ProtectionBit() == 0 {
main_data_size -= 2
}
// Read sideinfo from bitstream into buffer used by Bits()
buf := make([]byte, sideinfo_size)
n, err := source.ReadFull(buf)
if n < sideinfo_size {
if err == io.EOF {
return nil, &consts.UnexpectedEOF{"sideinfo.Read"}
}
return nil, fmt.Errorf("mp3: couldn't read sideinfo %d bytes: %v", sideinfo_size, err)
}
s := bits.New(buf)
mpeg1Frame := header.LowSamplingFrequency() == 0
bitsToRead := sideInfoBitsToRead[header.LowSamplingFrequency()]
// Parse audio data
// Pointer to where we should start reading main data
si := &SideInfo{}
si.MainDataBegin = s.Bits(bitsToRead[0])
// Get private bits. Not used for anything.
if header.Mode() == consts.ModeSingleChannel {
si.PrivateBits = s.Bits(bitsToRead[1])
} else {
si.PrivateBits = s.Bits(bitsToRead[2])
}
if mpeg1Frame {
// Get scale factor selection information
for ch := 0; ch < nch; ch++ {
for scfsi_band := 0; scfsi_band < 4; scfsi_band++ {
si.Scfsi[ch][scfsi_band] = s.Bits(1)
}
}
}
// Get the rest of the side information
for gr := 0; gr < header.Granules(); gr++ {
for ch := 0; ch < nch; ch++ {
si.Part2_3Length[gr][ch] = s.Bits(12)
si.BigValues[gr][ch] = s.Bits(9)
si.GlobalGain[gr][ch] = s.Bits(8)
si.ScalefacCompress[gr][ch] = s.Bits(bitsToRead[3])
si.WinSwitchFlag[gr][ch] = s.Bits(1)
if si.WinSwitchFlag[gr][ch] == 1 {
si.BlockType[gr][ch] = s.Bits(2)
si.MixedBlockFlag[gr][ch] = s.Bits(1)
for region := 0; region < 2; region++ {
si.TableSelect[gr][ch][region] = s.Bits(5)
}
for window := 0; window < 3; window++ {
si.SubblockGain[gr][ch][window] = s.Bits(3)
}
// TODO: This is not listed on the spec. Is this correct??
if si.BlockType[gr][ch] == 2 && si.MixedBlockFlag[gr][ch] == 0 {
si.Region0Count[gr][ch] = 8 // Implicit
} else {
si.Region0Count[gr][ch] = 7 // Implicit
}
// The standard is wrong on this!!!
// Implicit
si.Region1Count[gr][ch] = 20 - si.Region0Count[gr][ch]
} else {
for region := 0; region < 3; region++ {
si.TableSelect[gr][ch][region] = s.Bits(5)
}
si.Region0Count[gr][ch] = s.Bits(4)
si.Region1Count[gr][ch] = s.Bits(3)
si.BlockType[gr][ch] = 0 // Implicit
if !mpeg1Frame {
si.MixedBlockFlag[0][ch] = 0
}
}
if mpeg1Frame {
si.Preflag[gr][ch] = s.Bits(1)
}
si.ScalefacScale[gr][ch] = s.Bits(1)
si.Count1TableSelect[gr][ch] = s.Bits(1)
}
}
return si, nil
}