Matroska: scan for duration when not provided by metadata

Streamable files generally do not provide Duration via the header.
In order to support figuring out the duration of these files, we can
scan clusters from the start and the end of the file and give an
estimate that way.

Preserve parse_whole_file and hide_clusters functionality.

Author: hartman

getid3/module.audio-video.matroska.php

@@ -210,6 +210,11 @@
 define('EBML_ID_CLUSTERREFERENCEVIRTUAL',         0x7D); //             [FD] -- Relative position of the data that should be in position of the virtual block.
 
 
+/**
+ * Matroska constants
+ */
+define('MATROSKA_DEFAULT_TIMECODESCALE', 1000000);
+
 /**
 * @tutorial http://www.matroska.org/technical/specs/index.html
 *
@@ -241,6 +246,7 @@ class getid3_matroska extends getid3_handler
 	private $EBMLbuffer_length = 0;
 	private $current_offset    = 0;
 	private $unuseful_elements = array(EBML_ID_CRC32, EBML_ID_VOID);
+	private $parse_first_cluster = false;
 
 	/**
 	 * @return bool
@@ -256,14 +262,25 @@ public function Analyze()
 			$this->error('EBML parser: '.$e->getMessage());
 		}
 
-		// calculate playtime
-		if (isset($info['matroska']['info']) && is_array($info['matroska']['info'])) {
-			foreach ($info['matroska']['info'] as $key => $infoarray) {
-				if (isset($infoarray['Duration'])) {
-					// TimecodeScale is how many nanoseconds each Duration unit is
-					$info['playtime_seconds'] = $infoarray['Duration'] * ((isset($infoarray['TimecodeScale']) ? $infoarray['TimecodeScale'] : 1000000) / 1000000000);
-					break;
-				}
+		$this->calculatePlaytimeFromMetadata($info);
+
+		// If there was no duration metadata, this might be an incomplete file or a streaming file
+		// We need Cluster information so we can use their timecodes to estimate playtime.
+		if (!isset($info['playtime_seconds']) && !$this->parse_whole_file) {
+			// If we have not yet scanned the entire file, scan the start and end for Clusters,
+			$this->scanStartEndForClusters($info);
+		}
+
+		if (isset($info['matroska']['cluster']) && is_array($info['matroska']['cluster'])) {
+			if (!isset($info['playtime_seconds']) && !empty($info['matroska']['cluster'])) {
+				// estimate playtime using clusters if not yet known
+				$this->calculatePlaytimeFromClusters($info);
+			}
+
+			// Remove cluster information from output if hide_clusters is true
+			// These could have been set during scanStartEndForClusters()
+			if ($this->hide_clusters) {
+				unset($info['matroska']['cluster']);
 			}
 		}
 
@@ -1246,8 +1263,13 @@ private function parseEBML(&$info) {
 									}
 									$this->current_offset = $subelement['end'];
 								}
-								if (!$this->hide_clusters) {
-									$info['matroska']['cluster'][] = $cluster_entry;
+								// Always store clusters internally (for duration calculation)
+								// They will be removed from output later if hide_clusters is true
+								$info['matroska']['cluster'][] = $cluster_entry;
+
+								// Stop parsing after finding first cluster
+								if ($this->parse_first_cluster) {
+									return;
 								}
 
 								// check to see if all the data we need exists already, if so, break out of the loop
@@ -1919,4 +1941,114 @@ private static function getDefaultStreamInfo($streams)
 		return $info;
 	}
 
+	/**
+	 * @param array $info
+	 *
+	 * @return bool True if duration was set from metadata
+	 */
+	private function calculatePlaytimeFromMetadata(&$info) {
+		if (isset($info['matroska']['info']) && is_array($info['matroska']['info'])) {
+			foreach ($info['matroska']['info'] as $infoarray) {
+				if (isset($infoarray['Duration'])) {
+					// TimecodeScale is how many nanoseconds each Duration unit is
+					$info['playtime_seconds'] = $infoarray['Duration'] * ((isset($infoarray['TimecodeScale']) ? $infoarray['TimecodeScale'] : MATROSKA_DEFAULT_TIMECODESCALE) / 1000000000);
+					return true;
+				}
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * @param int $offset New starting offset for the buffer
+	 *
+	 * @return void
+	 */
+	private function resetParserBuffer($offset) {
+		$this->current_offset = $offset;
+		$this->EBMLbuffer = '';
+		$this->EBMLbuffer_offset = 0;
+		$this->EBMLbuffer_length = 0;
+	}
+
+	/**
+	 * Scan start and end of file for cluster information when Duration is missing
+	 * Only use this if no Duration was found in the Info element and we are not in parse_whole_file mode
+	 *
+	 * @param array $info
+	 *
+	 * @return void
+	 */
+	private function scanStartEndForClusters(&$info) {
+		$this->resetParserBuffer($info['avdataoffset']);
+
+		// we need to temporarily override parse_whole_file to be able to scan clusters
+		$this->parse_whole_file = true;
+		$this->parse_first_cluster = true;
+		try {
+			$this->parseEBML($info);
+		} catch (Exception $e) {
+			$this->error('EBML parser (start of file): '.$e->getMessage());
+		}
+		$this->parse_first_cluster = false;
+
+		// Scan end of file for last cluster
+		if (is_array($info['matroska']['cluster']) && !empty($info['matroska']['cluster'])) {
+			// maximum 1MB scan window before EOF
+			$this->resetParserBuffer(max(0, $info['avdataend'] - (1024 * 1024)));
+			try {
+				$this->parseEBML($info);
+			} catch (Exception $e) {
+				$this->error('EBML parser (end of file): '.$e->getMessage());
+			}
+		}
+		$this->parse_whole_file = false;
+	}
+
+	/**
+	 * Fetch TimecodeScale from Info element
+	 *
+	 * @param array $info
+	 *
+	 * @return int TimecodeScale value
+	 */
+	private function getTimecodeScale(&$info) {
+		$timecodeScale = MATROSKA_DEFAULT_TIMECODESCALE;
+		if (isset($info['matroska']['info']) && is_array($info['matroska']['info'])) {
+			foreach ($info['matroska']['info'] as $infoarray) {
+				if (isset($infoarray['TimecodeScale'])) {
+					$timecodeScale = $infoarray['TimecodeScale'];
+					break;
+				}
+			}
+		}
+		return $timecodeScale;
+	}
+
+	/**
+	 * Calculate duration from scanned cluster timecodes
+	 *
+	 * @param array $info
+	 *
+	 * @return void
+	 */
+	private function calculatePlaytimeFromClusters(&$info) {
+		$minTimecode = null;
+		$maxTimecode = null;
+		if (isset($info['matroska']['cluster']) && is_array($info['matroska']['cluster'])) {
+			foreach ($info['matroska']['cluster'] as $cluster) {
+				if (isset($cluster['ClusterTimecode'])) {
+					if ($minTimecode === null || $cluster['ClusterTimecode'] < $minTimecode) {
+						$minTimecode = $cluster['ClusterTimecode'];
+					}
+					if ($maxTimecode === null || $cluster['ClusterTimecode'] > $maxTimecode) {
+						$maxTimecode = $cluster['ClusterTimecode'];
+					}
+				}
+			}
+		}
+		if ($maxTimecode !== null && $minTimecode !== null && $maxTimecode > $minTimecode) {
+			$info['playtime_seconds'] = ($maxTimecode - $minTimecode) * ($this->getTimecodeScale($info) / 1000000000);
+		}
+	}
 }