module.audio.ac3.php

一个用PHP编写的

<?php
/////////////////////////////////////////////////////////////////
/// getID3() by James Heinrich <[e-mail]>               //
//  available at http://getid3.sourceforge.net                 //
//            or http://www.getid3.org                         //
/////////////////////////////////////////////////////////////////
// See readme.txt for more details                             //
/////////////////////////////////////////////////////////////////
//                                                             //
// module.audio.ac3.php                                        //
// module for analyzing AC-3 (aka Dolby Digital) audio files   //
// dependencies: NONE                                          //
//                                                            ///
/////////////////////////////////////////////////////////////////


class getid3_ac3
{

	function getid3_ac3(&$fd, &$ThisFileInfo) {

		///AH
		$ThisFileInfo['ac3']['raw']['bsi'] = array();
		$thisfile_ac3                      = &$ThisFileInfo['ac3'];
		$thisfile_ac3_raw                  = &$thisfile_ac3['raw'];
		$thisfile_ac3_raw_bsi              = &$thisfile_ac3_raw['bsi'];


		// http://www.atsc.org/standards/a_52a.pdf

		$ThisFileInfo['fileformat']            = 'ac3';
		$ThisFileInfo['audio']['dataformat']   = 'ac3';
		$ThisFileInfo['audio']['bitrate_mode'] = 'cbr';
		$ThisFileInfo['audio']['lossless']     = false;

		// An AC-3 serial coded audio bit stream is made up of a sequence of synchronization frames
		// Each synchronization frame contains 6 coded audio blocks (AB), each of which represent 256
		// new audio samples per channel. A synchronization information (SI) header at the beginning
		// of each frame contains information needed to acquire and maintain synchronization. A
		// bit stream information (BSI) header follows SI, and contains parameters describing the coded
		// audio service. The coded audio blocks may be followed by an auxiliary data (Aux) field. At the
		// end of each frame is an error check field that includes a CRC word for error detection. An
		// additional CRC word is located in the SI header, the use of which, by a decoder, is optional.
		//
		// syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC

		fseek($fd, $ThisFileInfo['avdataoffset'], SEEK_SET);
		$AC3header['syncinfo'] = fread($fd, 5);
		$thisfile_ac3_raw['synchinfo']['synchword'] = substr($AC3header['syncinfo'], 0, 2);

		if ($thisfile_ac3_raw['synchinfo']['synchword'] != "\x0B\x77") {

			$ThisFileInfo['error'][] = 'Expecting "\x0B\x77" at offset '.$ThisFileInfo['avdataoffset'].', found \x'.strtoupper(dechex($AC3header['syncinfo']{0})).'\x'.strtoupper(dechex($AC3header['syncinfo']{1})).' instead';
			unset($thisfile_ac3);
			return false;

		} else {

			// syncinfo() {
			// 	 syncword    16
			// 	 crc1        16
			// 	 fscod        2
			// 	 frmsizecod   6
			// } /* end of syncinfo */

			$thisfile_ac3_raw['synchinfo']['crc1']       = getid3_lib::LittleEndian2Int(substr($AC3header['syncinfo'], 2, 2));
			$ac3_synchinfo_fscod_frmsizecod                        = getid3_lib::LittleEndian2Int(substr($AC3header['syncinfo'], 4, 1));
			$thisfile_ac3_raw['synchinfo']['fscod']      = ($ac3_synchinfo_fscod_frmsizecod & 0xC0) >> 6;
			$thisfile_ac3_raw['synchinfo']['frmsizecod'] = ($ac3_synchinfo_fscod_frmsizecod & 0x3F);

			$thisfile_ac3['sample_rate'] = $this->AC3sampleRateCodeLookup($thisfile_ac3_raw['synchinfo']['fscod']);
			if ($thisfile_ac3_raw['synchinfo']['fscod'] <= 3) {
				$ThisFileInfo['audio']['sample_rate'] = $thisfile_ac3['sample_rate'];
			}

			$thisfile_ac3['frame_length'] = $this->AC3frameSizeLookup($thisfile_ac3_raw['synchinfo']['frmsizecod'], $thisfile_ac3_raw['synchinfo']['fscod']);
			$thisfile_ac3['bitrate']      = $this->AC3bitrateLookup($thisfile_ac3_raw['synchinfo']['frmsizecod']);
			$ThisFileInfo['audio']['bitrate'] = $thisfile_ac3['bitrate'];

			$AC3header['bsi'] = getid3_lib::BigEndian2Bin(fread($fd, 15));
			$ac3_bsi_offset = 0;

			$thisfile_ac3_raw_bsi['bsid'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 5));
			$ac3_bsi_offset += 5;
			if ($thisfile_ac3_raw_bsi['bsid'] > 8) {
				// Decoders which can decode version 8 will thus be able to decode version numbers less than 8.
				// If this standard is extended by the addition of additional elements or features, a value of bsid greater than 8 will be used.
				// Decoders built to this version of the standard will not be able to decode versions with bsid greater than 8.
				$ThisFileInfo['error'][] = 'Bit stream identification is version '.$thisfile_ac3_raw_bsi['bsid'].', but getID3() only understands up to version 8';
				unset($thisfile_ac3);
				return false;
			}

			$thisfile_ac3_raw_bsi['bsmod'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 3));
			$ac3_bsi_offset += 3;
			$thisfile_ac3_raw_bsi['acmod'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 3));
			$ac3_bsi_offset += 3;

			$thisfile_ac3['service_type'] = $this->AC3serviceTypeLookup($thisfile_ac3_raw_bsi['bsmod'], $thisfile_ac3_raw_bsi['acmod']);
			$ac3_coding_mode = $this->AC3audioCodingModeLookup($thisfile_ac3_raw_bsi['acmod']);
			foreach($ac3_coding_mode as $key => $value) {
				$thisfile_ac3[$key] = $value;
			}
			switch ($thisfile_ac3_raw_bsi['acmod']) {
				case 0:
				case 1:
					$ThisFileInfo['audio']['channelmode'] = 'mono';
					break;
				case 3:
				case 4:
					$ThisFileInfo['audio']['channelmode'] = 'stereo';
					break;
				default:
					$ThisFileInfo['audio']['channelmode'] = 'surround';
					break;
			}
			$ThisFileInfo['audio']['channels'] = $thisfile_ac3['num_channels'];

			if ($thisfile_ac3_raw_bsi['acmod'] & 0x01) {
				// If the lsb of acmod is a 1, center channel is in use and cmixlev follows in the bit stream.
				$thisfile_ac3_raw_bsi['cmixlev'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 2));
				$ac3_bsi_offset += 2;
				$thisfile_ac3['center_mix_level'] = $this->AC3centerMixLevelLookup($thisfile_ac3_raw_bsi['cmixlev']);
			}

			if ($thisfile_ac3_raw_bsi['acmod'] & 0x04) {
				// If the msb of acmod is a 1, surround channels are in use and surmixlev follows in the bit stream.
				$thisfile_ac3_raw_bsi['surmixlev'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 2));
				$ac3_bsi_offset += 2;
				$thisfile_ac3['surround_mix_level'] = $this->AC3surroundMixLevelLookup($thisfile_ac3_raw_bsi['surmixlev']);
			}

			if ($thisfile_ac3_raw_bsi['acmod'] == 0x02) {
				// When operating in the two channel mode, this 2-bit code indicates whether or not the program has been encoded in Dolby Surround.
				$thisfile_ac3_raw_bsi['dsurmod'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 2));
				$ac3_bsi_offset += 2;
				$thisfile_ac3['dolby_surround_mode'] = $this->AC3dolbySurroundModeLookup($thisfile_ac3_raw_bsi['dsurmod']);
			}

			$thisfile_ac3_raw_bsi['lfeon'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
			$ac3_bsi_offset += 1;
			$thisfile_ac3['lfe_enabled'] = $thisfile_ac3_raw_bsi['lfeon'];
			if ($thisfile_ac3_raw_bsi['lfeon']) {
				//$ThisFileInfo['audio']['channels']++;
				$ThisFileInfo['audio']['channels'] .= '.1';
			}

			$thisfile_ac3['channels_enabled'] = $this->AC3channelsEnabledLookup($thisfile_ac3_raw_bsi['acmod'], $thisfile_ac3_raw_bsi['lfeon']);

			// This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1