1<?php
2
3/////////////////////////////////////////////////////////////////
4/// getID3() by James Heinrich <info@getid3.org>               //
5//  available at https://github.com/JamesHeinrich/getID3       //
6//            or https://www.getid3.org                        //
7//            or http://getid3.sourceforge.net                 //
8//  see readme.txt for more details                            //
9/////////////////////////////////////////////////////////////////
10//                                                             //
11// module.audio.aa.php                                         //
12// module for analyzing Audible Audiobook files                //
13// dependencies: NONE                                          //
14//                                                            ///
15/////////////////////////////////////////////////////////////////
16
17if (!defined('GETID3_INCLUDEPATH')) { // prevent path-exposing attacks that access modules directly on public webservers
18	exit;
19}
20
21class getid3_amr extends getid3_handler
22{
23	/**
24	 * @return bool
25	 */
26	public function Analyze() {
27		$info = &$this->getid3->info;
28
29		$this->fseek($info['avdataoffset']);
30		$AMRheader = $this->fread(6);
31
32		$magic = '#!AMR'."\x0A";
33		if (substr($AMRheader, 0, 6) != $magic) {
34			$this->error('Expecting "'.getid3_lib::PrintHexBytes($magic).'" at offset '.$info['avdataoffset'].', found "'.getid3_lib::PrintHexBytes(substr($AMRheader, 0, 6)).'"');
35			return false;
36		}
37
38		// shortcut
39		$info['amr'] = array();
40		$thisfile_amr = &$info['amr'];
41
42		$info['fileformat']               = 'amr';
43		$info['audio']['dataformat']      = 'amr';
44		$info['audio']['bitrate_mode']    = 'vbr';   // within a small predefined range: 4.75kbps to 12.2kbps
45		$info['audio']['bits_per_sample'] =    13;   // http://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_codec: "Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz"
46		$info['audio']['sample_rate']     =  8000;   // http://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_codec: "Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz"
47		$info['audio']['channels']        =     1;
48		$thisfile_amr['frame_mode_count'] = array(0=>0, 1=>0, 2=>0, 3=>0, 4=>0, 5=>0, 6=>0, 7=>0);
49
50		$buffer = '';
51		do {
52			if ((strlen($buffer) < $this->getid3->fread_buffer_size()) && !feof($this->getid3->fp)) {
53				$buffer .= $this->fread($this->getid3->fread_buffer_size() * 2);
54			}
55			$AMR_frame_header = ord(substr($buffer, 0, 1));
56			$codec_mode_request = ($AMR_frame_header & 0x78) >> 3; // The 2nd bit through 5th bit (counting the most significant bit as the first bit) comprise the CMR (Codec Mode Request), values 0-7 being valid for AMR. The top bit of the CMR can actually be ignored, though it is used when AMR forms RTP payloads. The lower 3-bits of the header are reserved and are not used. Viewing the header from most significant bit to least significant bit, the encoding is XCCCCXXX, where Xs are reserved (typically 0) and the Cs are the CMR.
57			if ($codec_mode_request > 7) {
58				break;
59			}
60			$thisfile_amr['frame_mode_count'][$codec_mode_request]++;
61			$buffer = substr($buffer, $this->amr_mode_bytes_per_frame($codec_mode_request));
62		} while (strlen($buffer) > 0);
63
64		$info['playtime_seconds'] = array_sum($thisfile_amr['frame_mode_count']) * 0.020; // each frame contain 160 samples and is 20 milliseconds long
65		$info['audio']['bitrate'] = (8 * ($info['avdataend'] - $info['avdataoffset'])) / $info['playtime_seconds']; // bitrate could be calculated from average bitrate by distributation of frame types. That would give effective audio bitrate, this gives overall file bitrate which will be a little bit higher since every frame will waste 8 bits for header, plus a few bits for octet padding
66		$info['bitrate'] = $info['audio']['bitrate'];
67
68		return true;
69	}
70
71	/**
72	 * @param int $key
73	 *
74	 * @return int|false
75	 */
76	public function amr_mode_bitrate($key) {
77		static $amr_mode_bitrate = array(
78			0 =>  4750,
79			1 =>  5150,
80			2 =>  5900,
81			3 =>  6700,
82			4 =>  7400,
83			5 =>  7950,
84			6 => 10200,
85			7 => 12200,
86		);
87		return (isset($amr_mode_bitrate[$key]) ? $amr_mode_bitrate[$key] : false);
88	}
89
90	/**
91	 * @param int $key
92	 *
93	 * @return int|false
94	 */
95	public function amr_mode_bytes_per_frame($key) {
96		static $amr_mode_bitrate = array(
97			0 =>  13, // 1-byte frame header +  95 bits [padded to: 12 bytes] audio data
98			1 =>  14, // 1-byte frame header + 103 bits [padded to: 13 bytes] audio data
99			2 =>  16, // 1-byte frame header + 118 bits [padded to: 15 bytes] audio data
100			3 =>  18, // 1-byte frame header + 134 bits [padded to: 17 bytes] audio data
101			4 =>  20, // 1-byte frame header + 148 bits [padded to: 19 bytes] audio data
102			5 =>  21, // 1-byte frame header + 159 bits [padded to: 20 bytes] audio data
103			6 =>  27, // 1-byte frame header + 204 bits [padded to: 26 bytes] audio data
104			7 =>  32, // 1-byte frame header + 244 bits [padded to: 31 bytes] audio data
105		);
106		return (isset($amr_mode_bitrate[$key]) ? $amr_mode_bitrate[$key] : false);
107	}
108
109
110}
111