Custom data allows you to associate custom metadata with entries. It can be accessed via "evaluate" calls in javascript.

Listing all player metadata: The following code shows how to list all custom metadata for a entry.

kWidget.embed({
	'targetId': 'kaltura_player',
	'wid': '_243342',
	'uiconf_id': '12905712',
	'entry_id': '0_uka1msg4',
	'flashvars': {
		'metadataProfileId':  3282, // the metadata profile id from your account
		'requiredMetadataFields' : true 
	},
	'readyCallback': function( playerId ){
		var kdp = $( '#' + playerId )[0];
		kdp.addJsListener( 'metadataReceived', function (){
			var customDataList = kdp.evaluate('{mediaProxy.entryMetadata}');
			$.each( customDataList, function( key, val ){
				$('#customData').append( '<tr><td>' + key + '</td><td>' + val + '</td></tr>' );
			});
		});
	}
})

Pay attention to the metadataProfile id, set to 3282 per player.kaltura.com account, another valid test metadataProfile id for player.kaltura.com is 313142