ebiten/audio/mp3/read.go

266 lines
7.4 KiB
Go

// Copyright 2017 The Ebiten Authors
//
// 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.
// +build !js
package mp3
import (
"fmt"
"io"
)
func readCRC() error {
buf := make([]int, 2)
n := 0
var err error
for n < 2 && err == nil {
nn, err2 := getBytes(buf[n:])
n += nn
err = err2
}
if err == io.EOF {
if n < 2 {
return fmt.Errorf("mp3: unexpected EOF at readCRC")
}
return nil
}
if err != nil {
return err
}
return nil
}
func (f *frame) readNextFrame() (*frame, error) {
nf := &frame{
prev: f,
}
if nf.prev != nil {
nf.store = nf.prev.store
nf.v_vec = nf.prev.v_vec
}
h, err := readHeader()
if err != nil {
return nil, err
}
nf.header = h
// Get CRC word if present
if nf.header.protection_bit == 0 {
if err := readCRC(); err != nil {
return nil, err
}
}
if nf.header.layer != mpeg1Layer3 {
return nil, fmt.Errorf("mp3: only layer3 (want %d; got %d) is supported!", mpeg1Layer3, nf.header.layer)
}
// Get side info
s, err := readSideInfo(nf.header)
if err != nil {
return nil, err
}
nf.sideInfo = s
// If there's not enough main data in the bit reservoir,
// signal to calling function so that decoding isn't done!
// Get main data(scalefactors and Huffman coded frequency data)
if err := nf.readMainL3(); err != nil {
return nil, err
}
return nf, nil
}
func isHeader(header uint32) bool {
const C_SYNC = 0xffe00000
if (header & C_SYNC) != C_SYNC {
return false
}
// Bitrate must not be 15.
if (header & (0xf << 12)) == 0xf<<12 {
return false
}
// Sample Frequency must not be 3.
if (header & (3 << 10)) == 3<<10 {
return false
}
return true
}
func readHeader() (*mpeg1FrameHeader, error) {
// Get the next four bytes from the bitstream
buf := make([]int, 4)
n := 0
var err error
for n < 4 && err == nil {
nn, err2 := getBytes(buf[n:])
n += nn
err = err2
}
if n < 4 {
if err == io.EOF {
if n == 0 {
return nil, eof
}
return nil, fmt.Errorf("mp3: unexpected EOF at readHeader")
}
return nil, err
}
b1 := uint32(buf[0])
b2 := uint32(buf[1])
b3 := uint32(buf[2])
b4 := uint32(buf[3])
header := (b1 << 24) | (b2 << 16) | (b3 << 8) | (b4 << 0)
for !isHeader(uint32(header)) {
// No,so scan the bitstream one byte at a time until we find it or EOF
// Shift the values one byte to the left
b1 = b2
b2 = b3
b3 = b4
// Get one new byte from the bitstream
b, err := getByte()
if err != nil {
if err == io.EOF {
return nil, fmt.Errorf("mp3: unexpected EOF at readHeader")
}
return nil, err
}
b4 = uint32(b)
header = (b1 << 24) | (b2 << 16) | (b3 << 8) | (b4 << 0)
}
// If we get here we've found the sync word,and can decode the header
// which is in the low 20 bits of the 32-bit sync+header word.
// Decode the header
h := &mpeg1FrameHeader{}
h.id = int((header & 0x00180000) >> 19)
h.layer = mpeg1Layer((header & 0x00060000) >> 17)
h.protection_bit = int((header & 0x00010000) >> 16)
h.bitrate_index = int((header & 0x0000f000) >> 12)
h.sampling_frequency = int((header & 0x00000c00) >> 10)
h.padding_bit = int((header & 0x00000200) >> 9)
h.private_bit = int((header & 0x00000100) >> 8)
h.mode = mpeg1Mode((header & 0x000000c0) >> 6)
h.mode_extension = int((header & 0x00000030) >> 4)
h.copyright = int((header & 0x00000008) >> 3)
h.original_or_copy = int((header & 0x00000004) >> 2)
h.emphasis = int((header & 0x00000003) >> 0)
// Check for invalid values and impossible combinations
if h.id != 3 {
return nil, fmt.Errorf("mp3: ID must be 3. Header word is 0x%08x at file pos %d",
header, getFilepos())
}
if h.bitrate_index == 0 {
return nil, fmt.Errorf("mp3: Free bitrate format NIY! Header word is 0x%08x at file pos %d",
header, getFilepos())
}
if h.bitrate_index == 15 {
return nil, fmt.Errorf("mp3: bitrate_index = 15 is invalid! Header word is 0x%08x at file pos %d",
header, getFilepos())
}
if h.sampling_frequency == 3 {
return nil, fmt.Errorf("mp3: sampling_frequency = 3 is invalid! Header word is 0x%08x at file pos %d",
header, getFilepos())
}
if h.layer == mpeg1LayerReserved {
return nil, fmt.Errorf("mp3: layer = %d is invalid! Header word is 0x%08x at file pos %d",
mpeg1LayerReserved, header, getFilepos())
}
return h, nil
}
func (f *frame) readHuffman(part_2_start, gr, ch int) error {
// Check that there is any data to decode. If not,zero the array.
if f.sideInfo.part2_3_length[gr][ch] == 0 {
for is_pos := 0; is_pos < 576; is_pos++ {
f.mainData.is[gr][ch][is_pos] = 0.0
}
return nil
}
// Calculate bit_pos_end which is the index of the last bit for this part.
bit_pos_end := part_2_start + f.sideInfo.part2_3_length[gr][ch] - 1
// Determine region boundaries
region_1_start := 0
region_2_start := 0
if (f.sideInfo.win_switch_flag[gr][ch] == 1) && (f.sideInfo.block_type[gr][ch] == 2) {
region_1_start = 36 // sfb[9/3]*3=36
region_2_start = 576 // No Region2 for short block case.
} else {
sfreq := f.header.sampling_frequency
region_1_start =
sfBandIndicesSet[sfreq].l[f.sideInfo.region0_count[gr][ch]+1]
region_2_start =
sfBandIndicesSet[sfreq].l[f.sideInfo.region0_count[gr][ch]+
f.sideInfo.region1_count[gr][ch]+2]
}
// Read big_values using tables according to region_x_start
for is_pos := 0; is_pos < f.sideInfo.big_values[gr][ch]*2; is_pos++ {
table_num := 0
if is_pos < region_1_start {
table_num = f.sideInfo.table_select[gr][ch][0]
} else if is_pos < region_2_start {
table_num = f.sideInfo.table_select[gr][ch][1]
} else {
table_num = f.sideInfo.table_select[gr][ch][2]
}
// Get next Huffman coded words
x, y, _, _, err := huffmanDecode(f.mainDataBytes, table_num)
if err != nil {
return err
}
// In the big_values area there are two freq lines per Huffman word
f.mainData.is[gr][ch][is_pos] = float32(x)
is_pos++
f.mainData.is[gr][ch][is_pos] = float32(y)
}
// Read small values until is_pos = 576 or we run out of huffman data
table_num := f.sideInfo.count1table_select[gr][ch] + 32
is_pos := f.sideInfo.big_values[gr][ch] * 2
for (is_pos <= 572) && (f.mainDataBytes.getMainPos() <= bit_pos_end) {
// Get next Huffman coded words
x, y, v, w, err := huffmanDecode(f.mainDataBytes, table_num)
if err != nil {
return err
}
f.mainData.is[gr][ch][is_pos] = float32(v)
is_pos++
if is_pos >= 576 {
break
}
f.mainData.is[gr][ch][is_pos] = float32(w)
is_pos++
if is_pos >= 576 {
break
}
f.mainData.is[gr][ch][is_pos] = float32(x)
is_pos++
if is_pos >= 576 {
break
}
f.mainData.is[gr][ch][is_pos] = float32(y)
is_pos++
}
// Check that we didn't read past the end of this section
if f.mainDataBytes.getMainPos() > (bit_pos_end + 1) {
// Remove last words read
is_pos -= 4
}
// Setup count1 which is the index of the first sample in the rzero reg.
f.sideInfo.count1[gr][ch] = is_pos
// Zero out the last part if necessary
for is_pos < 576 {
f.mainData.is[gr][ch][is_pos] = 0.0
is_pos++
}
// Set the bitpos to point to the next part to read
f.mainDataBytes.setMainPos(bit_pos_end + 1)
return nil
}