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 /////////////////////////////////////////////////////////////////
10 // module.audio.ac3.php //
11 // module for analyzing AC-3 (aka Dolby Digital) audio files //
12 // dependencies: NONE //
14 /////////////////////////////////////////////////////////////////
17 class getid3_ac3 extends getid3_handler
19 private $AC3header = array();
20 private $BSIoffset = 0;
22 const syncword = "\x0B\x77";
24 public function Analyze() {
25 $info = &$this->getid3->info;
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'];
34 // http://www.atsc.org/standards/a_52a.pdf
36 $info['fileformat'] = 'ac3';
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.
47 // syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC
54 // } /* end of syncinfo */
56 $this->fseek($info['avdataoffset']);
57 $this->AC3header['syncinfo'] = $this->fread(5);
59 if (strpos($this->AC3header['syncinfo'], self::syncword) === 0) {
60 $thisfile_ac3_raw['synchinfo']['synchword'] = self::syncword;
63 if (!$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)).'"');
68 $this->fseek(-2, SEEK_CUR);
71 $info['audio']['dataformat'] = 'ac3';
72 $info['audio']['bitrate_mode'] = 'cbr';
73 $info['audio']['lossless'] = false;
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);
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'];
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'];
89 $this->AC3header['bsi'] = getid3_lib::BigEndian2Bin($this->fread(15));
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');
102 $thisfile_ac3_raw_bsi['bsmod'] = $this->readHeaderBSI(3);
103 $thisfile_ac3_raw_bsi['acmod'] = $this->readHeaderBSI(3);
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] = $value;
110 switch ($thisfile_ac3_raw_bsi['acmod']) {
113 $info['audio']['channelmode'] = 'mono';
117 $info['audio']['channelmode'] = 'stereo';
120 $info['audio']['channelmode'] = 'surround';
123 $info['audio']['channels'] = $thisfile_ac3['num_channels'];
125 if ($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']);
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']);
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']);
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';
150 $thisfile_ac3['channels_enabled'] = self::channelsEnabledLookup($thisfile_ac3_raw_bsi['acmod'], $thisfile_ac3_raw_bsi['lfeon']);
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';
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']);
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);
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);
173 $thisfile_ac3['mixing_level'] = (80 + $thisfile_ac3_raw_bsi['mixlevel']).'dB';
174 $thisfile_ac3['room_type'] = self::roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp']);
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.
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';
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']);
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);
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);
203 $thisfile_ac3['mixing_level2'] = (80 + $thisfile_ac3_raw_bsi['mixlevel2']).'dB';
204 $thisfile_ac3['room_type2'] = self::roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp2']);
209 $thisfile_ac3_raw_bsi['copyright'] = (bool) $this->readHeaderBSI(1);
211 $thisfile_ac3_raw_bsi['original'] = (bool) $this->readHeaderBSI(1);
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);
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);
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);
227 $this->AC3header['bsi'] .= getid3_lib::BigEndian2Bin($this->fread($thisfile_ac3_raw_bsi['addbsi_length']));
229 $thisfile_ac3_raw_bsi['addbsi_data'] = substr($this->AC3header['bsi'], $this->BSIoffset, $thisfile_ac3_raw_bsi['addbsi_length'] * 8);
230 $this->BSIoffset += $thisfile_ac3_raw_bsi['addbsi_length'] * 8;
236 private function readHeaderBSI($length) {
237 $data = substr($this->AC3header['bsi'], $this->BSIoffset, $length);
238 $this->BSIoffset += $length;
240 return bindec($data);
243 public static function sampleRateCodeLookup($fscod) {
244 static $sampleRateCodeLookup = array(
248 3 => 'reserved' // If the reserved code is indicated, the decoder should not attempt to decode audio and should mute.
250 return (isset($sampleRateCodeLookup[$fscod]) ? $sampleRateCodeLookup[$fscod] : false);
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)';
266 $serviceTypeLookup[7][1] = 'associated service: voice over (VO)';
267 for ($i = 2; $i <= 7; $i++) {
268 $serviceTypeLookup[7][$i] = 'main audio service: karaoke';
271 return (isset($serviceTypeLookup[$bsmod][$acmod]) ? $serviceTypeLookup[$bsmod][$acmod] : false);
274 public static function audioCodingModeLookup($acmod) {
275 // array(channel configuration, # channels (not incl LFE), channel order)
276 static $audioCodingModeLookup = array (
277 0 => array('channel_config'=>'1+1', 'num_channels'=>2, 'channel_order'=>'Ch1,Ch2'),
278 1 => array('channel_config'=>'1/0', 'num_channels'=>1, 'channel_order'=>'C'),
279 2 => array('channel_config'=>'2/0', 'num_channels'=>2, 'channel_order'=>'L,R'),
280 3 => array('channel_config'=>'3/0', 'num_channels'=>3, 'channel_order'=>'L,C,R'),
281 4 => array('channel_config'=>'2/1', 'num_channels'=>3, 'channel_order'=>'L,R,S'),
282 5 => array('channel_config'=>'3/1', 'num_channels'=>4, 'channel_order'=>'L,C,R,S'),
283 6 => array('channel_config'=>'2/2', 'num_channels'=>4, 'channel_order'=>'L,R,SL,SR'),
284 7 => array('channel_config'=>'3/2', 'num_channels'=>5, 'channel_order'=>'L,C,R,SL,SR'),
286 return (isset($audioCodingModeLookup[$acmod]) ? $audioCodingModeLookup[$acmod] : false);
289 public static function centerMixLevelLookup($cmixlev) {
290 static $centerMixLevelLookup;
291 if (empty($centerMixLevelLookup)) {
292 $centerMixLevelLookup = array(
293 0 => pow(2, -3.0 / 6), // 0.707 (-3.0 dB)
294 1 => pow(2, -4.5 / 6), // 0.595 (-4.5 dB)
295 2 => pow(2, -6.0 / 6), // 0.500 (-6.0 dB)
299 return (isset($centerMixLevelLookup[$cmixlev]) ? $centerMixLevelLookup[$cmixlev] : false);
302 public static function surroundMixLevelLookup($surmixlev) {
303 static $surroundMixLevelLookup;
304 if (empty($surroundMixLevelLookup)) {
305 $surroundMixLevelLookup = array(
306 0 => pow(2, -3.0 / 6),
307 1 => pow(2, -6.0 / 6),
312 return (isset($surroundMixLevelLookup[$surmixlev]) ? $surroundMixLevelLookup[$surmixlev] : false);
315 public static function dolbySurroundModeLookup($dsurmod) {
316 static $dolbySurroundModeLookup = array(
317 0 => 'not indicated',
318 1 => 'Not Dolby Surround encoded',
319 2 => 'Dolby Surround encoded',
322 return (isset($dolbySurroundModeLookup[$dsurmod]) ? $dolbySurroundModeLookup[$dsurmod] : false);
325 public static function channelsEnabledLookup($acmod, $lfeon) {
327 'ch1'=>(bool) ($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,
339 $lookup['surround_mono'] = true;
343 $lookup['surround_left'] = true;
344 $lookup['surround_right'] = true;
350 public static function heavyCompression($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.
360 // Meaning of 4 msb of compr
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));
382 $log_gain = bindec(substr($fourbit, 1));
384 $log_gain = ($log_gain + 1) * getid3_lib::RGADamplitude2dB(2);
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.
391 $lin_gain = (16 + ($compre & 0x0F)) / 32;
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.
397 return $log_gain - $lin_gain;
400 public static function roomTypeLookup($roomtyp) {
401 static $roomTypeLookup = array(
402 0 => 'not indicated',
403 1 => 'large room, X curve monitor',
404 2 => 'small room, flat monitor',
407 return (isset($roomTypeLookup[$roomtyp]) ? $roomTypeLookup[$roomtyp] : false);
410 public static function frameSizeLookup($frmsizecod, $fscod) {
411 $padding = (bool) ($frmsizecod % 2);
412 $framesizeid = floor($frmsizecod / 2);
414 static $frameSizeLookup = array();
415 if (empty($frameSizeLookup)) {
416 $frameSizeLookup = array (
417 0 => array(128, 138, 192),
418 1 => array(40, 160, 174, 240),
419 2 => array(48, 192, 208, 288),
420 3 => array(56, 224, 242, 336),
421 4 => array(64, 256, 278, 384),
422 5 => array(80, 320, 348, 480),
423 6 => array(96, 384, 416, 576),
424 7 => array(112, 448, 486, 672),
425 8 => array(128, 512, 556, 768),
426 9 => array(160, 640, 696, 960),
427 10 => array(192, 768, 834, 1152),
428 11 => array(224, 896, 974, 1344),
429 12 => array(256, 1024, 1114, 1536),
430 13 => array(320, 1280, 1392, 1920),
431 14 => array(384, 1536, 1670, 2304),
432 15 => array(448, 1792, 1950, 2688),
433 16 => array(512, 2048, 2228, 3072),
434 17 => array(576, 2304, 2506, 3456),
435 18 => array(640, 2560, 2786, 3840)
438 if (($fscod == 1) && $padding) {
439 // frame lengths are padded by 1 word (16 bits) at 44100
440 $frameSizeLookup[$frmsizecod] += 2;
442 return (isset($frameSizeLookup[$framesizeid][$fscod]) ? $frameSizeLookup[$framesizeid][$fscod] : false);
445 public static function bitrateLookup($frmsizecod) {
446 $framesizeid = floor($frmsizecod / 2);
448 static $bitrateLookup = array(
469 return (isset($bitrateLookup[$framesizeid]) ? $bitrateLookup[$framesizeid] : false);