Shadow Sync Sample Box table provides an optional set of sync * samples that can be used when seeking or for similar purposes. In normal * forward play they are ignored. * * Each entry in the Shadow Sync Table consists of a pair of sample numbers. The * first entry (shadowedSampleNumber) indicates the number of the sample that a * shadow sync will be defined for. This should always be a non-sync sample * (e.g. a frame difference). The second sample number (syncSampleNumber) * indicates the sample number of the sync sample (i.e. key frame) that can be * used when there is a random access at, or before, the shadowedSampleNumber. * * The shadow sync samples are normally placed in an area of the track that is * not presented during normal play (edited out by means of an edit list), * though this is not a requirement. The shadow sync table can be ignored and * the track will play (and seek) correctly if it is ignored (though perhaps not * optimally). * * The Shadow Sync Sample replaces, not augments, the sample that it shadows * (i.e. the next sample sent is shadowedSampleNumber+1). The shadow sync sample * is treated as if it occurred at the time of the sample it shadows, having the * duration of the sample it shadows. * * Hinting and transmission might become more complex if a shadow sample is used * also as part of normal playback, or is used more than once as a shadow. In * this case the hint track might need separate shadow syncs, all of which can * get their media data from the one shadow sync in the media track, to allow * for the different time-stamps etc. needed in their headers. * * @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_STSH extends ISO14496_Box_Full { /** @var Array */ private $_shadowSyncSampleTable = 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); $entryCount = $this->_reader->readUInt32BE(); $data = $this->_reader->read ($this->getOffset() + $this->getSize() - $this->_reader->getOffset()); for ($i = 0; $i < $entryCount; $i++) $this->_shadowSyncSampleTable[$i] = array ("shadowedSampleNumber" => Transform::fromUInt32BE(substr($data, ($i - 1) * 8, 4)), "syncSampleNumber" => Transform::fromUInt32BE(substr($data, $i * 8 - 4, 4))); } /** * Returns an array of values. Each entry is an array containing the following * keys. * o shadowedSampleNumber - gives the number of a sample for which there is * an alternative sync sample. * o syncSampleNumber - gives the number of the alternative sync sample. * * @return Array */ public function getShadowSyncSampleTable() { return $this->_shadowSyncSampleTable; } }