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  • Committer: Jacek Nykis
  • Date: 2015-01-05 16:17:05 UTC
  • Revision ID: jacek.nykis@canonical.com-20150105161705-w544l1h5mcg7u4w9
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wp-includes/ID3/module.audio.ac3.php
 
1
<?php
 
2
/////////////////////////////////////////////////////////////////
 
3
/// getID3() by James Heinrich <info@getid3.org>               //
 
4
//  available at http://getid3.sourceforge.net                 //
 
5
//            or http://www.getid3.org                         //
 
6
/////////////////////////////////////////////////////////////////
 
7
// See readme.txt for more details                             //
 
8
/////////////////////////////////////////////////////////////////
 
9
//                                                             //
 
10
// module.audio.ac3.php                                        //
 
11
// module for analyzing AC-3 (aka Dolby Digital) audio files   //
 
12
// dependencies: NONE                                          //
 
13
//                                                            ///
 
14
/////////////////////////////////////////////////////////////////
 
15
 
 
16
 
 
17
class getid3_ac3 extends getid3_handler
 
18
{
 
19
    private $AC3header = array();
 
20
    private $BSIoffset = 0;
 
21
 
 
22
    const syncword = "\x0B\x77";
 
23
 
 
24
        public function Analyze() {
 
25
                $info = &$this->getid3->info;
 
26
 
 
27
                ///AH
 
28
                $info['ac3']['raw']['bsi'] = array();
 
29
                $thisfile_ac3              = &$info['ac3'];
 
30
                $thisfile_ac3_raw          = &$thisfile_ac3['raw'];
 
31
                $thisfile_ac3_raw_bsi      = &$thisfile_ac3_raw['bsi'];
 
32
 
 
33
 
 
34
                // http://www.atsc.org/standards/a_52a.pdf
 
35
 
 
36
                $info['fileformat'] = 'ac3';
 
37
 
 
38
                // An AC-3 serial coded audio bit stream is made up of a sequence of synchronization frames
 
39
                // Each synchronization frame contains 6 coded audio blocks (AB), each of which represent 256
 
40
                // new audio samples per channel. A synchronization information (SI) header at the beginning
 
41
                // of each frame contains information needed to acquire and maintain synchronization. A
 
42
                // bit stream information (BSI) header follows SI, and contains parameters describing the coded
 
43
                // audio service. The coded audio blocks may be followed by an auxiliary data (Aux) field. At the
 
44
                // end of each frame is an error check field that includes a CRC word for error detection. An
 
45
                // additional CRC word is located in the SI header, the use of which, by a decoder, is optional.
 
46
                //
 
47
                // syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC
 
48
 
 
49
                // syncinfo() {
 
50
                //       syncword    16
 
51
                //       crc1        16
 
52
                //       fscod        2
 
53
                //       frmsizecod   6
 
54
                // } /* end of syncinfo */
 
55
 
 
56
                $this->fseek($info['avdataoffset']);
 
57
                $this->AC3header['syncinfo'] = $this->fread(5);
 
58
 
 
59
                if (strpos($this->AC3header['syncinfo'], self::syncword) === 0) {
 
60
                        $thisfile_ac3_raw['synchinfo']['synchword'] = self::syncword;
 
61
                        $offset = 2;
 
62
                } else {
 
63
                        if (!$this->isDependencyFor('matroska')) {
 
64
                                unset($info['fileformat'], $info['ac3']);
 
65
                                return $this->error('Expecting "'.getid3_lib::PrintHexBytes(self::syncword).'" at offset '.$info['avdataoffset'].', found "'.getid3_lib::PrintHexBytes(substr($this->AC3header['syncinfo'], 0, 2)).'"');
 
66
                        }
 
67
                        $offset = 0;
 
68
                        $this->fseek(-2, SEEK_CUR);
 
69
                }
 
70
 
 
71
                $info['audio']['dataformat']   = 'ac3';
 
72
                $info['audio']['bitrate_mode'] = 'cbr';
 
73
                $info['audio']['lossless']     = false;
 
74
 
 
75
                $thisfile_ac3_raw['synchinfo']['crc1']       = getid3_lib::LittleEndian2Int(substr($this->AC3header['syncinfo'], $offset, 2));
 
76
                $ac3_synchinfo_fscod_frmsizecod              = getid3_lib::LittleEndian2Int(substr($this->AC3header['syncinfo'], ($offset + 2), 1));
 
77
                $thisfile_ac3_raw['synchinfo']['fscod']      = ($ac3_synchinfo_fscod_frmsizecod & 0xC0) >> 6;
 
78
                $thisfile_ac3_raw['synchinfo']['frmsizecod'] = ($ac3_synchinfo_fscod_frmsizecod & 0x3F);
 
79
 
 
80
                $thisfile_ac3['sample_rate'] = self::sampleRateCodeLookup($thisfile_ac3_raw['synchinfo']['fscod']);
 
81
                if ($thisfile_ac3_raw['synchinfo']['fscod'] <= 3) {
 
82
                        $info['audio']['sample_rate'] = $thisfile_ac3['sample_rate'];
 
83
                }
 
84
 
 
85
                $thisfile_ac3['frame_length'] = self::frameSizeLookup($thisfile_ac3_raw['synchinfo']['frmsizecod'], $thisfile_ac3_raw['synchinfo']['fscod']);
 
86
                $thisfile_ac3['bitrate']      = self::bitrateLookup($thisfile_ac3_raw['synchinfo']['frmsizecod']);
 
87
                $info['audio']['bitrate'] = $thisfile_ac3['bitrate'];
 
88
 
 
89
                $this->AC3header['bsi'] = getid3_lib::BigEndian2Bin($this->fread(15));
 
90
                $ac3_bsi_offset = 0;
 
91
 
 
92
                $thisfile_ac3_raw_bsi['bsid'] = $this->readHeaderBSI(5);
 
93
                if ($thisfile_ac3_raw_bsi['bsid'] > 8) {
 
94
                        // Decoders which can decode version 8 will thus be able to decode version numbers less than 8.
 
95
                        // If this standard is extended by the addition of additional elements or features, a value of bsid greater than 8 will be used.
 
96
                        // Decoders built to this version of the standard will not be able to decode versions with bsid greater than 8.
 
97
                        $this->error('Bit stream identification is version '.$thisfile_ac3_raw_bsi['bsid'].', but getID3() only understands up to version 8');
 
98
                    unset($info['ac3']);
 
99
                        return false;
 
100
                }
 
101
 
 
102
                $thisfile_ac3_raw_bsi['bsmod'] = $this->readHeaderBSI(3);
 
103
                $thisfile_ac3_raw_bsi['acmod'] = $this->readHeaderBSI(3);
 
104
 
 
105
                $thisfile_ac3['service_type'] = self::serviceTypeLookup($thisfile_ac3_raw_bsi['bsmod'], $thisfile_ac3_raw_bsi['acmod']);
 
106
                $ac3_coding_mode = self::audioCodingModeLookup($thisfile_ac3_raw_bsi['acmod']);
 
107
                foreach($ac3_coding_mode as $key => $value) {
 
108
                        $thisfile_ac3[$key] = $value;
 
109
                }
 
110
                switch ($thisfile_ac3_raw_bsi['acmod']) {
 
111
                        case 0:
 
112
                        case 1:
 
113
                                $info['audio']['channelmode'] = 'mono';
 
114
                                break;
 
115
                        case 3:
 
116
                        case 4:
 
117
                                $info['audio']['channelmode'] = 'stereo';
 
118
                                break;
 
119
                        default:
 
120
                                $info['audio']['channelmode'] = 'surround';
 
121
                                break;
 
122
                }
 
123
                $info['audio']['channels'] = $thisfile_ac3['num_channels'];
 
124
 
 
125
                if ($thisfile_ac3_raw_bsi['acmod'] & 0x01) {
 
126
                        // If the lsb of acmod is a 1, center channel is in use and cmixlev follows in the bit stream.
 
127
                        $thisfile_ac3_raw_bsi['cmixlev'] = $this->readHeaderBSI(2);
 
128
                        $thisfile_ac3['center_mix_level'] = self::centerMixLevelLookup($thisfile_ac3_raw_bsi['cmixlev']);
 
129
                }
 
130
 
 
131
                if ($thisfile_ac3_raw_bsi['acmod'] & 0x04) {
 
132
                        // If the msb of acmod is a 1, surround channels are in use and surmixlev follows in the bit stream.
 
133
                        $thisfile_ac3_raw_bsi['surmixlev'] = $this->readHeaderBSI(2);
 
134
                        $thisfile_ac3['surround_mix_level'] = self::surroundMixLevelLookup($thisfile_ac3_raw_bsi['surmixlev']);
 
135
                }
 
136
 
 
137
                if ($thisfile_ac3_raw_bsi['acmod'] == 0x02) {
 
138
                        // When operating in the two channel mode, this 2-bit code indicates whether or not the program has been encoded in Dolby Surround.
 
139
                        $thisfile_ac3_raw_bsi['dsurmod'] = $this->readHeaderBSI(2);
 
140
                        $thisfile_ac3['dolby_surround_mode'] = self::dolbySurroundModeLookup($thisfile_ac3_raw_bsi['dsurmod']);
 
141
                }
 
142
 
 
143
                $thisfile_ac3_raw_bsi['lfeon'] = (bool) $this->readHeaderBSI(1);
 
144
                $thisfile_ac3['lfe_enabled'] = $thisfile_ac3_raw_bsi['lfeon'];
 
145
                if ($thisfile_ac3_raw_bsi['lfeon']) {
 
146
                        //$info['audio']['channels']++;
 
147
                        $info['audio']['channels'] .= '.1';
 
148
                }
 
149
 
 
150
                $thisfile_ac3['channels_enabled'] = self::channelsEnabledLookup($thisfile_ac3_raw_bsi['acmod'], $thisfile_ac3_raw_bsi['lfeon']);
 
151
 
 
152
                // This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1-31.
 
153
                // The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.
 
154
                $thisfile_ac3_raw_bsi['dialnorm'] = $this->readHeaderBSI(5);
 
155
                $thisfile_ac3['dialogue_normalization'] = '-'.$thisfile_ac3_raw_bsi['dialnorm'].'dB';
 
156
 
 
157
                $thisfile_ac3_raw_bsi['compre_flag'] = (bool) $this->readHeaderBSI(1);
 
158
                if ($thisfile_ac3_raw_bsi['compre_flag']) {
 
159
                        $thisfile_ac3_raw_bsi['compr'] = $this->readHeaderBSI(8);
 
160
                        $thisfile_ac3['heavy_compression'] = self::heavyCompression($thisfile_ac3_raw_bsi['compr']);
 
161
                }
 
162
 
 
163
                $thisfile_ac3_raw_bsi['langcode_flag'] = (bool) $this->readHeaderBSI(1);
 
164
                if ($thisfile_ac3_raw_bsi['langcode_flag']) {
 
165
                        $thisfile_ac3_raw_bsi['langcod'] = $this->readHeaderBSI(8);
 
166
                }
 
167
 
 
168
                $thisfile_ac3_raw_bsi['audprodie'] = (bool) $this->readHeaderBSI(1);
 
169
                if ($thisfile_ac3_raw_bsi['audprodie']) {
 
170
                        $thisfile_ac3_raw_bsi['mixlevel'] = $this->readHeaderBSI(5);
 
171
                        $thisfile_ac3_raw_bsi['roomtyp']  = $this->readHeaderBSI(2);
 
172
 
 
173
                        $thisfile_ac3['mixing_level'] = (80 + $thisfile_ac3_raw_bsi['mixlevel']).'dB';
 
174
                        $thisfile_ac3['room_type']    = self::roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp']);
 
175
                }
 
176
 
 
177
                if ($thisfile_ac3_raw_bsi['acmod'] == 0x00) {
 
178
                        // If acmod is 0, then two completely independent program channels (dual mono)
 
179
                        // are encoded into the bit stream, and are referenced as Ch1, Ch2. In this case,
 
180
                        // a number of additional items are present in BSI or audblk to fully describe Ch2.
 
181
 
 
182
                        // This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1-31.
 
183
                        // The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.
 
184
                        $thisfile_ac3_raw_bsi['dialnorm2'] = $this->readHeaderBSI(5);
 
185
                        $thisfile_ac3['dialogue_normalization2'] = '-'.$thisfile_ac3_raw_bsi['dialnorm2'].'dB';
 
186
 
 
187
                        $thisfile_ac3_raw_bsi['compre_flag2'] = (bool) $this->readHeaderBSI(1);
 
188
                        if ($thisfile_ac3_raw_bsi['compre_flag2']) {
 
189
                                $thisfile_ac3_raw_bsi['compr2'] = $this->readHeaderBSI(8);
 
190
                                $thisfile_ac3['heavy_compression2'] = self::heavyCompression($thisfile_ac3_raw_bsi['compr2']);
 
191
                        }
 
192
 
 
193
                        $thisfile_ac3_raw_bsi['langcode_flag2'] = (bool) $this->readHeaderBSI(1);
 
194
                        if ($thisfile_ac3_raw_bsi['langcode_flag2']) {
 
195
                                $thisfile_ac3_raw_bsi['langcod2'] = $this->readHeaderBSI(8);
 
196
                        }
 
197
 
 
198
                        $thisfile_ac3_raw_bsi['audprodie2'] = (bool) $this->readHeaderBSI(1);
 
199
                        if ($thisfile_ac3_raw_bsi['audprodie2']) {
 
200
                                $thisfile_ac3_raw_bsi['mixlevel2'] = $this->readHeaderBSI(5);
 
201
                                $thisfile_ac3_raw_bsi['roomtyp2']  = $this->readHeaderBSI(2);
 
202
 
 
203
                                $thisfile_ac3['mixing_level2'] = (80 + $thisfile_ac3_raw_bsi['mixlevel2']).'dB';
 
204
                                $thisfile_ac3['room_type2']    = self::roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp2']);
 
205
                        }
 
206
 
 
207
                }
 
208
 
 
209
                $thisfile_ac3_raw_bsi['copyright'] = (bool) $this->readHeaderBSI(1);
 
210
 
 
211
                $thisfile_ac3_raw_bsi['original']  = (bool) $this->readHeaderBSI(1);
 
212
 
 
213
                $thisfile_ac3_raw_bsi['timecode1_flag'] = (bool) $this->readHeaderBSI(1);
 
214
                if ($thisfile_ac3_raw_bsi['timecode1_flag']) {
 
215
                        $thisfile_ac3_raw_bsi['timecode1'] = $this->readHeaderBSI(14);
 
216
                }
 
217
 
 
218
                $thisfile_ac3_raw_bsi['timecode2_flag'] = (bool) $this->readHeaderBSI(1);
 
219
                if ($thisfile_ac3_raw_bsi['timecode2_flag']) {
 
220
                        $thisfile_ac3_raw_bsi['timecode2'] = $this->readHeaderBSI(14);
 
221
                }
 
222
 
 
223
                $thisfile_ac3_raw_bsi['addbsi_flag'] = (bool) $this->readHeaderBSI(1);
 
224
                if ($thisfile_ac3_raw_bsi['addbsi_flag']) {
 
225
                        $thisfile_ac3_raw_bsi['addbsi_length'] = $this->readHeaderBSI(6);
 
226
 
 
227
                        $this->AC3header['bsi'] .= getid3_lib::BigEndian2Bin($this->fread($thisfile_ac3_raw_bsi['addbsi_length']));
 
228
 
 
229
                        $thisfile_ac3_raw_bsi['addbsi_data'] = substr($this->AC3header['bsi'], $this->BSIoffset, $thisfile_ac3_raw_bsi['addbsi_length'] * 8);
 
230
                        $this->BSIoffset += $thisfile_ac3_raw_bsi['addbsi_length'] * 8;
 
231
                }
 
232
 
 
233
                return true;
 
234
        }
 
235
 
 
236
        private function readHeaderBSI($length) {
 
237
                $data = substr($this->AC3header['bsi'], $this->BSIoffset, $length);
 
238
                $this->BSIoffset += $length;
 
239
 
 
240
                return bindec($data);
 
241
        }
 
242
 
 
243
        public static function sampleRateCodeLookup($fscod) {
 
244
                static $sampleRateCodeLookup = array(
 
245
                        0 => 48000,
 
246
                        1 => 44100,
 
247
                        2 => 32000,
 
248
                        3 => 'reserved' // If the reserved code is indicated, the decoder should not attempt to decode audio and should mute.
 
249
                );
 
250
                return (isset($sampleRateCodeLookup[$fscod]) ? $sampleRateCodeLookup[$fscod] : false);
 
251
        }
 
252
 
 
253
        public static function serviceTypeLookup($bsmod, $acmod) {
 
254
                static $serviceTypeLookup = array();
 
255
                if (empty($serviceTypeLookup)) {
 
256
                        for ($i = 0; $i <= 7; $i++) {
 
257
                                $serviceTypeLookup[0][$i] = 'main audio service: complete main (CM)';
 
258
                                $serviceTypeLookup[1][$i] = 'main audio service: music and effects (ME)';
 
259
                                $serviceTypeLookup[2][$i] = 'associated service: visually impaired (VI)';
 
260
                                $serviceTypeLookup[3][$i] = 'associated service: hearing impaired (HI)';
 
261
                                $serviceTypeLookup[4][$i] = 'associated service: dialogue (D)';
 
262
                                $serviceTypeLookup[5][$i] = 'associated service: commentary (C)';
 
263
                                $serviceTypeLookup[6][$i] = 'associated service: emergency (E)';
 
264
                        }
 
265
 
 
266
                        $serviceTypeLookup[7][1]      = 'associated service: voice over (VO)';
 
267
                        for ($i = 2; $i <= 7; $i++) {
 
268
                                $serviceTypeLookup[7][$i] = 'main audio service: karaoke';
 
269
                        }
 
270
                }
 
271
                return (isset($serviceTypeLookup[$bsmod][$acmod]) ? $serviceTypeLookup[$bsmod][$acmod] : false);
 
272
        }
 
273
 
 
274
        public static function audioCodingModeLookup($acmod) {
 
275
                // array(channel configuration, # channels (not incl LFE), channel order)
 
276
                static $audioCodingModeLookup = array (
 
277
                        0 => array('channel_config'=>'1+1', 'num_channels'=>2, 'channel_order'=>'Ch1,Ch2'),
 
278
                        1 => array('channel_config'=>'1/0', 'num_channels'=>1, 'channel_order'=>'C'),
 
279
                        2 => array('channel_config'=>'2/0', 'num_channels'=>2, 'channel_order'=>'L,R'),
 
280
                        3 => array('channel_config'=>'3/0', 'num_channels'=>3, 'channel_order'=>'L,C,R'),
 
281
                        4 => array('channel_config'=>'2/1', 'num_channels'=>3, 'channel_order'=>'L,R,S'),
 
282
                        5 => array('channel_config'=>'3/1', 'num_channels'=>4, 'channel_order'=>'L,C,R,S'),
 
283
                        6 => array('channel_config'=>'2/2', 'num_channels'=>4, 'channel_order'=>'L,R,SL,SR'),
 
284
                        7 => array('channel_config'=>'3/2', 'num_channels'=>5, 'channel_order'=>'L,C,R,SL,SR'),
 
285
                );
 
286
                return (isset($audioCodingModeLookup[$acmod]) ? $audioCodingModeLookup[$acmod] : false);
 
287
        }
 
288
 
 
289
        public static function centerMixLevelLookup($cmixlev) {
 
290
                static $centerMixLevelLookup;
 
291
                if (empty($centerMixLevelLookup)) {
 
292
                        $centerMixLevelLookup = array(
 
293
                                0 => pow(2, -3.0 / 6), // 0.707 (-3.0 dB)
 
294
                                1 => pow(2, -4.5 / 6), // 0.595 (-4.5 dB)
 
295
                                2 => pow(2, -6.0 / 6), // 0.500 (-6.0 dB)
 
296
                                3 => 'reserved'
 
297
                        );
 
298
                }
 
299
                return (isset($centerMixLevelLookup[$cmixlev]) ? $centerMixLevelLookup[$cmixlev] : false);
 
300
        }
 
301
 
 
302
        public static function surroundMixLevelLookup($surmixlev) {
 
303
                static $surroundMixLevelLookup;
 
304
                if (empty($surroundMixLevelLookup)) {
 
305
                        $surroundMixLevelLookup = array(
 
306
                                0 => pow(2, -3.0 / 6),
 
307
                                1 => pow(2, -6.0 / 6),
 
308
                                2 => 0,
 
309
                                3 => 'reserved'
 
310
                        );
 
311
                }
 
312
                return (isset($surroundMixLevelLookup[$surmixlev]) ? $surroundMixLevelLookup[$surmixlev] : false);
 
313
        }
 
314
 
 
315
        public static function dolbySurroundModeLookup($dsurmod) {
 
316
                static $dolbySurroundModeLookup = array(
 
317
                        0 => 'not indicated',
 
318
                        1 => 'Not Dolby Surround encoded',
 
319
                        2 => 'Dolby Surround encoded',
 
320
                        3 => 'reserved'
 
321
                );
 
322
                return (isset($dolbySurroundModeLookup[$dsurmod]) ? $dolbySurroundModeLookup[$dsurmod] : false);
 
323
        }
 
324
 
 
325
        public static function channelsEnabledLookup($acmod, $lfeon) {
 
326
                $lookup = array(
 
327
                        'ch1'=>(bool) ($acmod == 0),
 
328
                        'ch2'=>(bool) ($acmod == 0),
 
329
                        'left'=>(bool) ($acmod > 1),
 
330
                        'right'=>(bool) ($acmod > 1),
 
331
                        'center'=>(bool) ($acmod & 0x01),
 
332
                        'surround_mono'=>false,
 
333
                        'surround_left'=>false,
 
334
                        'surround_right'=>false,
 
335
                        'lfe'=>$lfeon);
 
336
                switch ($acmod) {
 
337
                        case 4:
 
338
                        case 5:
 
339
                                $lookup['surround_mono']  = true;
 
340
                                break;
 
341
                        case 6:
 
342
                        case 7:
 
343
                                $lookup['surround_left']  = true;
 
344
                                $lookup['surround_right'] = true;
 
345
                                break;
 
346
                }
 
347
                return $lookup;
 
348
        }
 
349
 
 
350
        public static function heavyCompression($compre) {
 
351
                // The first four bits indicate gain changes in 6.02dB increments which can be
 
352
                // implemented with an arithmetic shift operation. The following four bits
 
353
                // indicate linear gain changes, and require a 5-bit multiply.
 
354
                // We will represent the two 4-bit fields of compr as follows:
 
355
                //   X0 X1 X2 X3 . Y4 Y5 Y6 Y7
 
356
                // The meaning of the X values is most simply described by considering X to represent a 4-bit
 
357
                // signed integer with values from -8 to +7. The gain indicated by X is then (X + 1) * 6.02 dB. The
 
358
                // following table shows this in detail.
 
359
 
 
360
                // Meaning of 4 msb of compr
 
361
                //  7    +48.16 dB
 
362
                //  6    +42.14 dB
 
363
                //  5    +36.12 dB
 
364
                //  4    +30.10 dB
 
365
                //  3    +24.08 dB
 
366
                //  2    +18.06 dB
 
367
                //  1    +12.04 dB
 
368
                //  0     +6.02 dB
 
369
                // -1         0 dB
 
370
                // -2     -6.02 dB
 
371
                // -3    -12.04 dB
 
372
                // -4    -18.06 dB
 
373
                // -5    -24.08 dB
 
374
                // -6    -30.10 dB
 
375
                // -7    -36.12 dB
 
376
                // -8    -42.14 dB
 
377
 
 
378
                $fourbit = str_pad(decbin(($compre & 0xF0) >> 4), 4, '0', STR_PAD_LEFT);
 
379
                if ($fourbit{0} == '1') {
 
380
                        $log_gain = -8 + bindec(substr($fourbit, 1));
 
381
                } else {
 
382
                        $log_gain = bindec(substr($fourbit, 1));
 
383
                }
 
384
                $log_gain = ($log_gain + 1) * getid3_lib::RGADamplitude2dB(2);
 
385
 
 
386
                // The value of Y is a linear representation of a gain change of up to -6 dB. Y is considered to
 
387
                // be an unsigned fractional integer, with a leading value of 1, or: 0.1 Y4 Y5 Y6 Y7 (base 2). Y can
 
388
                // represent values between 0.111112 (or 31/32) and 0.100002 (or 1/2). Thus, Y can represent gain
 
389
                // changes from -0.28 dB to -6.02 dB.
 
390
 
 
391
                $lin_gain = (16 + ($compre & 0x0F)) / 32;
 
392
 
 
393
                // The combination of X and Y values allows compr to indicate gain changes from
 
394
                //  48.16 - 0.28 = +47.89 dB, to
 
395
                // -42.14 - 6.02 = -48.16 dB.
 
396
 
 
397
                return $log_gain - $lin_gain;
 
398
        }
 
399
 
 
400
        public static function roomTypeLookup($roomtyp) {
 
401
                static $roomTypeLookup = array(
 
402
                        0 => 'not indicated',
 
403
                        1 => 'large room, X curve monitor',
 
404
                        2 => 'small room, flat monitor',
 
405
                        3 => 'reserved'
 
406
                );
 
407
                return (isset($roomTypeLookup[$roomtyp]) ? $roomTypeLookup[$roomtyp] : false);
 
408
        }
 
409
 
 
410
        public static function frameSizeLookup($frmsizecod, $fscod) {
 
411
                $padding     = (bool) ($frmsizecod % 2);
 
412
                $framesizeid =   floor($frmsizecod / 2);
 
413
 
 
414
                static $frameSizeLookup = array();
 
415
                if (empty($frameSizeLookup)) {
 
416
                        $frameSizeLookup = array (
 
417
                                0  => array(128, 138, 192),
 
418
                                1  => array(40, 160, 174, 240),
 
419
                                2  => array(48, 192, 208, 288),
 
420
                                3  => array(56, 224, 242, 336),
 
421
                                4  => array(64, 256, 278, 384),
 
422
                                5  => array(80, 320, 348, 480),
 
423
                                6  => array(96, 384, 416, 576),
 
424
                                7  => array(112, 448, 486, 672),
 
425
                                8  => array(128, 512, 556, 768),
 
426
                                9  => array(160, 640, 696, 960),
 
427
                                10 => array(192, 768, 834, 1152),
 
428
                                11 => array(224, 896, 974, 1344),
 
429
                                12 => array(256, 1024, 1114, 1536),
 
430
                                13 => array(320, 1280, 1392, 1920),
 
431
                                14 => array(384, 1536, 1670, 2304),
 
432
                                15 => array(448, 1792, 1950, 2688),
 
433
                                16 => array(512, 2048, 2228, 3072),
 
434
                                17 => array(576, 2304, 2506, 3456),
 
435
                                18 => array(640, 2560, 2786, 3840)
 
436
                        );
 
437
                }
 
438
                if (($fscod == 1) && $padding) {
 
439
                        // frame lengths are padded by 1 word (16 bits) at 44100
 
440
                        $frameSizeLookup[$frmsizecod] += 2;
 
441
                }
 
442
                return (isset($frameSizeLookup[$framesizeid][$fscod]) ? $frameSizeLookup[$framesizeid][$fscod] : false);
 
443
        }
 
444
 
 
445
        public static function bitrateLookup($frmsizecod) {
 
446
                $framesizeid =   floor($frmsizecod / 2);
 
447
 
 
448
                static $bitrateLookup = array(
 
449
                        0  => 32000,
 
450
                        1  => 40000,
 
451
                        2  => 48000,
 
452
                        3  => 56000,
 
453
                        4  => 64000,
 
454
                        5  => 80000,
 
455
                        6  => 96000,
 
456
                        7  => 112000,
 
457
                        8  => 128000,
 
458
                        9  => 160000,
 
459
                        10 => 192000,
 
460
                        11 => 224000,
 
461
                        12 => 256000,
 
462
                        13 => 320000,
 
463
                        14 => 384000,
 
464
                        15 => 448000,
 
465
                        16 => 512000,
 
466
                        17 => 576000,
 
467
                        18 => 640000
 
468
                );
 
469
                return (isset($bitrateLookup[$framesizeid]) ? $bitrateLookup[$framesizeid] : false);
 
470
        }
 
471
 
 
472
 
 
473
}