Added calculateFrameCount() and calculateDuration(); close #22

README.md

@@ -28,7 +28,16 @@ player.stop();
 // An 'onload' callback can be specified in the 'options' argument
 var mpegLoaded = function( player ) {
 	console.log('Loaded', player);
-}
+	
+	// calculateFrameCount() and calculateDuration() can only be called
+	// after the mpeg has been fully loaded. So this callback is the ideal
+	// place to fetch this info
+	var frames = player.calculateFrameCount(),
+		duration = player.calculateDuration();
+		
+	console.log('Duration: '+duration+' seconds ('+frames+' frames)');
+};
+
 var player = new jsmpeg('file.mpeg', {onload:mpegLoaded});
 
 // If you don't use 'autoplay' and don't explicitly call .play(), you can get individual

jsmpg.js

@@ -361,6 +361,31 @@ jsmpeg.prototype.fillArray = function(a, value) {
 	}
 };
 
+jsmpeg.prototype.cachedFrameCount = 0;
+jsmpeg.prototype.calculateFrameCount = function() {
+	if( !this.buffer || this.cachedFrameCount ) { 
+		return this.cachedFrameCount; 
+	}
+	
+	// Remember the buffer position, so we can rewind to the beginning and 
+	// reset to the current position afterwards
+	var currentPlaybackIndex = this.buffer.index,
+		frames = 0;
+	
+	this.buffer.index = 0;
+	while( this.findStartCode(START_PICTURE) !== BitReader.NOT_FOUND ) {
+		frames++;
+	}
+	this.buffer.index = currentPlaybackIndex;
+	
+	this.cachedFrameCount = frames;
+	return frames;
+};
+
+jsmpeg.prototype.calculateDuration = function() {
+	return this.calculateFrameCount() * (1/this.pictureRate);
+};
+
 
 
 // ----------------------------------------------------------------------------