Sample To Group Box table can be used to find the group that a * sample belongs to and the associated description of that sample group. The * table is compactly coded with each entry giving the index of the first sample * of a run of samples with the same sample group descriptor. The sample group * description ID is an index that refers to a {@link ISO14496_Box_SGPD Sample * Group Description Box}, which contains entries describing the characteristics * of each sample group. * * There may be multiple instances of this box if there is more than one sample * grouping for the samples in a track. Each instance of the Sample To Group Box * has a type code that distinguishes different sample groupings. Within a * track, there shall be at most one instance of this box with a particular * grouping type. The associated Sample Group Description shall indicate the * same value for the grouping type. * * @package php-reader * @subpackage ISO 14496 * @author Sven Vollbehr * @copyright Copyright (c) 2008 The PHP Reader Project Workgroup * @license http://code.google.com/p/php-reader/wiki/License New BSD License * @version $Rev: 92 $ */ final class ISO14496_Box_SBGP extends ISO14496_Box_Full { /** @var integer */ private $_groupingType; /** @var Array */ private $_sampleToGroupTable = array(); /** * Constructs the class with given parameters and reads box related data from * the ISO Base Media file. * * @param Reader $reader The reader object. */ public function __construct($reader, &$options = array()) { parent::__construct($reader, $options); $groupingType = $this->_reader->readUInt32BE(); $entryCount = $this->_reader->readUInt32BE(); $data = $this->_reader->read ($this->getOffset() + $this->getSize() - $this->_reader->getOffset()); for ($i = 1; $i <= $entryCount; $i++) $this->_sampleToGroupTable[$i] = array ("sampleCount" => Transform::fromUInt32BE(substr($data, ($i - 1) * 8, 4)), "groupDescriptionIndex" => Transform::fromUInt32BE(substr($data, $i * 8 - 4, 4))); } /** * Returns the grouping type that identifies the type (i.e. criterion used to * form the sample groups) of the sample grouping and links it to its sample * group description table with the same value for grouping type. At most one * occurrence of this box with the same value for groupingType shall exist for * a track. * * @return integer */ public function getGroupingType() { return $this->_groupingType; } /** * Returns an array of values. Each entry is an array containing the following * keys. * o sampleCount -- an integer that gives the number of consecutive samples * with the same sample group descriptor. If the sum of the sample count * in this box is less than the total sample count, then the reader should * effectively extend it with an entry that associates the remaining * samples with no group. It is an error for the total in this box to be * greater than the sample_count documented elsewhere, and the reader * behavior would then be undefined. * o groupDescriptionIndex -- an integer that gives the index of the sample * group entry which describes the samples in this group. The index ranges * from 1 to the number of sample group entries in the * {@link ISO14496_Box_SGPD Sample Group Description Box}, or takes the * value 0 to indicate that this sample is a member of no group of this * type. * * @return Array */ public function getSampleToGroupTable() { return $this->_sampleToGroupTable; } }