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audio/mp3: Refactoring

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This commit is contained in:
Hajime Hoshi 2017-06-18 17:40:28 +09:00
parent 2767136947
commit 1c779b6017
1 changed files with 16 additions and 15 deletions
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31
audio/mp3/sideinfo.go
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@ -23,44 +23,44 @@ import (
func readSideInfo(header *mpeg1FrameHeader) (*mpeg1SideInfo, error) { func readSideInfo(header *mpeg1FrameHeader) (*mpeg1SideInfo, error) {
nch := header.numberOfChannels() nch := header.numberOfChannels()
/* Calculate header audio data size */ // Calculate header audio data size
framesize := header.frameSize() framesize := header.frameSize()
if framesize > 2000 { if framesize > 2000 {
return nil, fmt.Errorf("mp3: framesize = %d\n", framesize) return nil, fmt.Errorf("mp3: framesize = %d\n", framesize)
} }
/* Sideinfo is 17 bytes for one channel and 32 bytes for two */ // Sideinfo is 17 bytes for one channel and 32 bytes for two
sideinfo_size := 32 sideinfo_size := 32
if nch == 1 { if nch == 1 {
sideinfo_size = 17 sideinfo_size = 17
} }
/* Main data size is the rest of the frame,including ancillary data */ // Main data size is the rest of the frame,including ancillary data
main_data_size := framesize - sideinfo_size - 4 /* sync+header */ main_data_size := framesize - sideinfo_size - 4 // sync+header
/* CRC is 2 bytes */ // CRC is 2 bytes
if header.protection_bit == 0 { if header.protection_bit == 0 {
main_data_size -= 2 main_data_size -= 2
} }
/* Read sideinfo from bitstream into buffer used by getSideBits() */ // Read sideinfo from bitstream into buffer used by getSideBits()
s, err := getSideinfo(sideinfo_size) s, err := getSideinfo(sideinfo_size)
if err != nil { if err != nil {
return nil, err return nil, err
} }
/* Parse audio data */ // Parse audio data
/* Pointer to where we should start reading main data */ // Pointer to where we should start reading main data
si := &mpeg1SideInfo{} si := &mpeg1SideInfo{}
si.main_data_begin = s.getSideBits(9) si.main_data_begin = s.getSideBits(9)
/* Get private bits. Not used for anything. */ // Get private bits. Not used for anything.
if header.mode == mpeg1ModeSingleChannel { if header.mode == mpeg1ModeSingleChannel {
si.private_bits = s.getSideBits(5) si.private_bits = s.getSideBits(5)
} else { } else {
si.private_bits = s.getSideBits(3) si.private_bits = s.getSideBits(3)
} }
/* Get scale factor selection information */ // Get scale factor selection information
for ch := 0; ch < nch; ch++ { for ch := 0; ch < nch; ch++ {
for scfsi_band := 0; scfsi_band < 4; scfsi_band++ { for scfsi_band := 0; scfsi_band < 4; scfsi_band++ {
si.scfsi[ch][scfsi_band] = s.getSideBits(1) si.scfsi[ch][scfsi_band] = s.getSideBits(1)
} }
} }
/* Get the rest of the side information */ // Get the rest of the side information
for gr := 0; gr < 2; gr++ { for gr := 0; gr < 2; gr++ {
for ch := 0; ch < nch; ch++ { for ch := 0; ch < nch; ch++ {
si.part2_3_length[gr][ch] = s.getSideBits(12) si.part2_3_length[gr][ch] = s.getSideBits(12)
@ -78,11 +78,12 @@ func readSideInfo(header *mpeg1FrameHeader) (*mpeg1SideInfo, error) {
si.subblock_gain[gr][ch][window] = s.getSideBits(3) si.subblock_gain[gr][ch][window] = s.getSideBits(3)
} }
if (si.block_type[gr][ch] == 2) && (si.mixed_block_flag[gr][ch] == 0) { if (si.block_type[gr][ch] == 2) && (si.mixed_block_flag[gr][ch] == 0) {
si.region0_count[gr][ch] = 8 /* Implicit */ si.region0_count[gr][ch] = 8 // Implicit
} else { } else {
si.region0_count[gr][ch] = 7 /* Implicit */ si.region0_count[gr][ch] = 7 // Implicit
} }
/* The standard is wrong on this!!! */ /* Implicit */ // The standard is wrong on this!!!
// Implicit
si.region1_count[gr][ch] = 20 - si.region0_count[gr][ch] si.region1_count[gr][ch] = 20 - si.region0_count[gr][ch]
} else { } else {
for region := 0; region < 3; region++ { for region := 0; region < 3; region++ {
@ -90,7 +91,7 @@ func readSideInfo(header *mpeg1FrameHeader) (*mpeg1SideInfo, error) {
} }
si.region0_count[gr][ch] = s.getSideBits(4) si.region0_count[gr][ch] = s.getSideBits(4)
si.region1_count[gr][ch] = s.getSideBits(3) si.region1_count[gr][ch] = s.getSideBits(3)
si.block_type[gr][ch] = 0 /* Implicit */ si.block_type[gr][ch] = 0 // Implicit
} }
si.preflag[gr][ch] = s.getSideBits(1) si.preflag[gr][ch] = s.getSideBits(1)
si.scalefac_scale[gr][ch] = s.getSideBits(1) si.scalefac_scale[gr][ch] = s.getSideBits(1)