Recipe 14.13 Seeking Relative to the Total Stream Length

14.13.1 Problem

You want to seek a stream based on the total length of the stream.

14.13.2 Solution

Get the stream length from the server and then use the seek( ) method.

14.13.3 Discussion

A problem arises when you want to seek within a stream relative to the total length of the stream. For example, if you want to create a slider that a user can move to seek through a stream, you must determine the total length of a stream. There is no client-side property or method that returns that information. However, you can write a server-side function to return a stream's length using the Stream.length( ) method. Here are the steps to return a stream's length from the server:

1. In the server-side .asc file (either the main.asc file or another .asc file that is loaded by main.asc) create a method for client objects that takes the name of a stream and returns the length of that stream (see Recipe 14.4). Most often, you assign methods to a client in the application.onConnect( ) method.

   // The application.onConnect(  ) method is invoked automatically whenever a new // client connects to the FlashCom application. The client object is created and // passed as a parameter to the method. application.onConnect = function (newClient) {   // Create a custom getStreamLength(  ) method for each client. The method takes   // the name of a stream as a parameter.   newClient.getStreamLength = function (streamName) {     // Return the length of the requested stream.     return Stream.length(streamName);   }; };

2. In the client-side ActionScript, connect to the FlashCom application:

   myConnection = new NetConnection(  ); myConnection.connect("rtmp:/myApp");

3. Create a response object to handle the result from the call to getStreamLength( ). A response object is an object created from the Object class, for which you have defined an onResult( ) method. When the onResult( ) method is invoked by a response from the FlashCom server, a result is returned from FlashCom and passed to the method as a parameter:

   myResponse = new Object(  ); myResponse.onResult = function (result) {   _root.streamLength = result;   trace("the stream length is: " + result); };

4. Once a connection is established and a response object is defined, call the server-side getStreamLength( ) method using the call( ) method of the client-side connection object. Specify that any response should be handled by the response object you created in the previous step and pass along the name of the stream as a parameter.

   myConnection.call("getStreamLength", myResponse, "myStreamName");

Once you have retrieved the total length of the stream, you can use that value in conjunction with a slider controller to determine values to pass to the seek( ) method. Here is an example:

// Create the connection. myConnection = new NetConnection(  ); myConnection.connect("rtmp:/myApp"); // Create the net stream. This example assumes that the stream is an audio-only // stream for which we don't want to control the volume or panning, so we don't need // to attach any audio or video. subscribe_ns = new NetStream(myConnection); // Create the response object. myResponse = new Object(  ); myResponse.onResult = function (result) {   // Assign the stream length to a variable on _root.   _root.streamLength = result;   // Begin the playback of the stream.   _root.subscribe_ns.play("myStreamName");   // Use an interval to call updateScroll(  ) to continually update the scroll position   // so that it corresponds to the stream position.   setInterval(_root, "updateScroll", 100); }; // Call the server-side getStreamLength(  ) method. We're assuming you created this // already in your main.asc file (or other loaded .asc). myConnection.call("getStreamLength", myResponse, "myStreamName"); // Create an isMouseDown variable, and toggle its value depending on the mouse state. // We use this to determine whether the user is scrolling or if the scrollbar is // being updated by the sound playback progress. _root.onMouseDown = function (  ) {   _root.isMouseDown = true; }; _root.onMouseUp = function (  ) {   _root.isMouseDown = false; }; // Create a callback function for the scrollbar. function onScroll (sb) {   // Perform the enclosed actions only if the user is scrolling, not if the scrollbar   // position is being updated due to the progress of sound playback.   if (_root.isMouseDown && scrollBar_sb.hitTest(_root._xmouse, _root._ymouse)) {     // Get the current scroll position of the scrollbar (from 0 to 100).     var percent = sb.getScrollPosition(  );     // Calculate the seconds value that correspond to the percentage based on the     // total stream length.     var seconds = percent * streamLength / 100;     // Seek to the appropriate point in the stream.     subscribe_ns.seek(seconds);   } } // This function updates the position of the scrollbar based on the current playback  // position of the stream. function updateScroll (  ) {   if (!_root.isMouseDown && !scrollBar_sb.hitTest(_root._xmouse, _root._ymouse)) {     var position = subscribe_ns.duration / streamLength * 100;     scrollBar_sb.setScrollPosition(position);   } } // Set the scrollbar properties and assign the change handler callback function. This // example assumes that you have created a  scrollbar instance on the Stage with a // name of scrollBar_sb. scrollBar_sb.setScrollProperties(10, 0, 100); scrollBar_sb.setChangeHandler("onScroll");

14.13.4 See Also

Recipe 14.12, Recipe 14.14, and Recipe 14.16