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audio/mp3: Refactoring

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This commit is contained in:
Hajime Hoshi 2017-06-18 02:38:43 +09:00
parent 93c48e15c0
commit 3a55c2f805
1 changed files with 41 additions and 46 deletions
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87
audio/mp3/maindata.go
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@ -28,39 +28,38 @@ var mpeg1_scalefac_sizes = [16][2]int{
func (f *frame) readMainL3() error {
nch := f.numberOfChannels()
/* Calculate header audio data size */
// Calculate header audio data size
framesize := (144*
g_mpeg1_bitrates[f.header.layer][f.header.bitrate_index])/
g_sampling_frequency[f.header.sampling_frequency] +
int(f.header.padding_bit)
f.header.padding_bit
if framesize > 2000 {
return fmt.Errorf("mp3: framesize = %d", 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
if nch == 1 {
sideinfo_size = 17
}
/* 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 */
// 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 f.header.protection_bit == 0 {
main_data_size -= 2
}
/* Assemble main data buffer with data from this frame and the previous
* two frames. main_data_begin indicates how many bytes from previous
* frames that should be used. This buffer is later accessed by the
* getMainBits function in the same way as the side info is.
*/
if err := getMainData(main_data_size, int(f.sideInfo.main_data_begin)); err != nil {
/* This could be due to not enough data in reservoir */
// Assemble main data buffer with data from this frame and the previous
// two frames. main_data_begin indicates how many bytes from previous
// frames that should be used. This buffer is later accessed by the
// getMainBits function in the same way as the side info is.
if err := getMainData(main_data_size, f.sideInfo.main_data_begin); err != nil {
// This could be due to not enough data in reservoir
return err
}
for gr := 0; gr < 2; gr++ {
for ch := 0; ch < nch; ch++ {
part_2_start := getMainPos()
/* Number of bits in the bitstream for the bands */
// Number of bits in the bitstream for the bands
slen1 := mpeg1_scalefac_sizes[f.sideInfo.scalefac_compress[gr][ch]][0]
slen2 := mpeg1_scalefac_sizes[f.sideInfo.scalefac_compress[gr][ch]][1]
if (f.sideInfo.win_switch_flag[gr][ch] != 0) && (f.sideInfo.block_type[gr][ch] == 2) {
@ -69,7 +68,7 @@ func (f *frame) readMainL3() error {
f.mainData.scalefac_l[gr][ch][sfb] = getMainBits(slen1)
}
for sfb := 3; sfb < 12; sfb++ {
/*slen1 for band 3-5,slen2 for 6-11*/
//slen1 for band 3-5,slen2 for 6-11
nbits := slen2
if sfb < 6 {
nbits = slen1
@ -80,7 +79,7 @@ func (f *frame) readMainL3() error {
}
} else {
for sfb := 0; sfb < 12; sfb++ {
/*slen1 for band 3-5,slen2 for 6-11*/
//slen1 for band 3-5,slen2 for 6-11
nbits := slen2
if sfb < 6 {
nbits = slen1
@ -90,59 +89,59 @@ func (f *frame) readMainL3() error {
}
}
}
} else { /* block_type == 0 if winswitch == 0 */
/* Scale factor bands 0-5 */
} else { // block_type == 0 if winswitch == 0
// Scale factor bands 0-5
if (f.sideInfo.scfsi[ch][0] == 0) || (gr == 0) {
for sfb := 0; sfb < 6; sfb++ {
f.mainData.scalefac_l[gr][ch][sfb] = getMainBits(slen1)
}
} else if (f.sideInfo.scfsi[ch][0] == 1) && (gr == 1) {
/* Copy scalefactors from granule 0 to granule 1 */
// Copy scalefactors from granule 0 to granule 1
for sfb := 0; sfb < 6; sfb++ {
f.mainData.scalefac_l[1][ch][sfb] = f.mainData.scalefac_l[0][ch][sfb]
}
}
/* Scale factor bands 6-10 */
// Scale factor bands 6-10
if (f.sideInfo.scfsi[ch][1] == 0) || (gr == 0) {
for sfb := 6; sfb < 11; sfb++ {
f.mainData.scalefac_l[gr][ch][sfb] = getMainBits(slen1)
}
} else if (f.sideInfo.scfsi[ch][1] == 1) && (gr == 1) {
/* Copy scalefactors from granule 0 to granule 1 */
// Copy scalefactors from granule 0 to granule 1
for sfb := 6; sfb < 11; sfb++ {
f.mainData.scalefac_l[1][ch][sfb] = f.mainData.scalefac_l[0][ch][sfb]
}
}
/* Scale factor bands 11-15 */
// Scale factor bands 11-15
if (f.sideInfo.scfsi[ch][2] == 0) || (gr == 0) {
for sfb := 11; sfb < 16; sfb++ {
f.mainData.scalefac_l[gr][ch][sfb] = getMainBits(slen2)
}
} else if (f.sideInfo.scfsi[ch][2] == 1) && (gr == 1) {
/* Copy scalefactors from granule 0 to granule 1 */
// Copy scalefactors from granule 0 to granule 1
for sfb := 11; sfb < 16; sfb++ {
f.mainData.scalefac_l[1][ch][sfb] = f.mainData.scalefac_l[0][ch][sfb]
}
}
/* Scale factor bands 16-20 */
// Scale factor bands 16-20
if (f.sideInfo.scfsi[ch][3] == 0) || (gr == 0) {
for sfb := 16; sfb < 21; sfb++ {
f.mainData.scalefac_l[gr][ch][sfb] = getMainBits(slen2)
}
} else if (f.sideInfo.scfsi[ch][3] == 1) && (gr == 1) {
/* Copy scalefactors from granule 0 to granule 1 */
// Copy scalefactors from granule 0 to granule 1
for sfb := 16; sfb < 21; sfb++ {
f.mainData.scalefac_l[1][ch][sfb] = f.mainData.scalefac_l[0][ch][sfb]
}
}
}
/* Read Huffman coded data. Skip stuffing bits. */
// Read Huffman coded data. Skip stuffing bits.
if err := f.readHuffman(part_2_start, gr, ch); err != nil {
return err
}
}
}
/* The ancillary data is stored here,but we ignore it. */
// The ancillary data is stored here,but we ignore it.
return nil
}
@ -166,7 +165,7 @@ func getMainData(size int, begin int) error {
return fmt.Errorf("mp3: size = %d", size)
}
// Check that there's data available from previous frames if needed
if int(begin) > theMainDataBytes.top {
if begin > theMainDataBytes.top {
// No,there is not, so we skip decoding this frame, but we have to
// read the main_data bits from the bitstream in case they are needed
// for decoding the next frame.
@ -185,7 +184,7 @@ func getMainData(size int, begin int) error {
return err
}
copy(theMainDataBytes.vec[theMainDataBytes.top:], buf[:n])
/* Set up pointers */
// Set up pointers
theMainDataBytes.ptr = theMainDataBytes.vec[0:]
theMainDataBytes.pos = 0
theMainDataBytes.idx = 0
@ -193,11 +192,9 @@ func getMainData(size int, begin int) error {
// TODO: Define a special error and enable to continue the next frame.
return fmt.Errorf("mp3: frame can't be decoded")
}
/* Copy data from previous frames */
for i := 0; i < begin; i++ {
theMainDataBytes.vec[i] = theMainDataBytes.vec[theMainDataBytes.top-begin+i]
}
/* Read the main_data from file */
// Copy data from previous frames
copy(theMainDataBytes.vec[:begin], theMainDataBytes.vec[theMainDataBytes.top-begin:theMainDataBytes.top])
// Read the main_data from file
buf := make([]int, size)
n := 0
var err error
@ -213,7 +210,7 @@ func getMainData(size int, begin int) error {
return err
}
copy(theMainDataBytes.vec[begin:], buf[:n])
/* Set up pointers */
// Set up pointers
theMainDataBytes.ptr = theMainDataBytes.vec[0:]
theMainDataBytes.pos = 0
theMainDataBytes.idx = 0
@ -234,7 +231,7 @@ func getMainBits(num int) int {
if num == 0 {
return 0
}
/* Form a word of the next four bytes */
// Form a word of the next four bytes
b := make([]int, 4)
for i := range b {
if len(theMainDataBytes.ptr) > i {
@ -243,30 +240,28 @@ func getMainBits(num int) int {
}
tmp := (uint32(b[0]) << 24) | (uint32(b[1]) << 16) | (uint32(b[2]) << 8) | (uint32(b[3]) << 0)
/* Remove bits already used */
// Remove bits already used
tmp = tmp << uint(theMainDataBytes.idx)
/* Remove bits after the desired bits */
// Remove bits after the desired bits
tmp = tmp >> (32 - uint(num))
/* Update pointers */
theMainDataBytes.ptr = theMainDataBytes.ptr[(theMainDataBytes.idx+int(num))>>3:]
// Update pointers
theMainDataBytes.ptr = theMainDataBytes.ptr[(theMainDataBytes.idx+num)>>3:]
theMainDataBytes.pos += (theMainDataBytes.idx + num) >> 3
theMainDataBytes.idx = (theMainDataBytes.idx + num) & 0x07
/* Done */
return int(tmp)
}
func getMainPos() int {
pos := theMainDataBytes.pos
pos *= 8 /* Multiply by 8 to get number of bits */
pos += theMainDataBytes.idx /* Add current bit index */
pos *= 8 // Multiply by 8 to get number of bits
pos += theMainDataBytes.idx
return pos
}
func setMainPos(bit_pos int) {
theMainDataBytes.ptr = theMainDataBytes.vec[bit_pos>>3:]
theMainDataBytes.pos = int(bit_pos) >> 3
theMainDataBytes.idx = int(bit_pos) & 0x7
theMainDataBytes.pos = bit_pos >> 3
theMainDataBytes.idx = bit_pos & 0x7
}