Recipe 16.4. Reading Video Duration

Problem

You want to read the total length (duration) of a video.

Solution

Use an onMetaData( ) callback and read the duration metadata value.

Discussion

The NetStream class does not define a property that reports the total length of a Flash video. However, in most cases, it is possible to read that value from the FLV file itself. FLV files can contain metadata, and almost all video encoders include a duration metadata value, which stores the length of the video in seconds (which can be fractions of seconds). Assuming the FLV has a duration metadata value, you can read that value with ActionScript.

When a NetStream object is loading an FLV file, it automatically calls an onMetaData( ) callback method when the metadata has loaded. The callback model differs from the standard event model used by most of the ActionScript 3.0 APIs. In most cases in which you work with events you add a listener using addEventListener( ). However, in the case of metadata events you must define an onMetaData( ) method for an object and then assign that object to the client property of the NetStream object. The method is automatically passed an associative array parameter typed as Object that contains properties and values corresponding to each of the metadata properties that have been read from the FLV. The following example uses trace( ) to display the duration metadata value of a video clip:

var client:Object = new Object(  ); client.onMetaData = function(metadata:Object):void {     trace(metadata.duration); }; videoStream.client = client;

In practice, the preceding example isn't all that useful. Rather, you're more likely to assign a function reference to the onMetaData property of the NetStream object. When the function is called, it is called with the correct scope. The following example class loads, plays back a video, and displays the playback time and duration:

package {     import flash.display.TextField;     import flash.media.Video;     import flash.net.NetConnection;     import flash.net.NetStream;     import flash.events.NetStatusEvent;     import flash.display.TextFieldAutoSize;     import flash.display.Sprite;     import flash.events.Event;          public class Example extends Sprite {         private var _stream:NetStream;         private var _video:Video;         private var _playbackTime:TextField;         private var _duration:uint;                  public function Example(  ) {             _video = new Video(160, 120);             _playbackTime = new TextField(  );             _playbackTime.autoSize = TextFieldAutoSize.LEFT;             _playbackTime.y = 120;             _playbackTime.text = "test";             _duration = 0;             var connection:NetConnection = new NetConnection(  );             connection.connect(null);             _stream = new NetStream(connection);             _stream.play("video.flv");             var client:Object = new Object(  );             client.onMetaData = onMetaData;             _stream.client = client;             _video.attachNetStream(_stream);             addChild(_video);             addChild(_playbackTime);             addEventListener(Event.ENTER_FRAME, onEnterFrame);         }         private function onMetaData(data:Object):void {             _duration = data.duration;         }                  private function onEnterFrame(event:Event):void {             if(_duration > 0 && _stream.time > 0) {                 _playbackTime.text = Math.round(_stream.time) + " / " +                  Math.round(_duration);             }         }                      } }

See Also

Recipe 16.8