播放受保护内容的工作流程

创建 MediaPlayer 实例。
```
player = new MediaPlayer();
```
向播放器注册 MediaPlayerCapabilityChangeEvent.HAS_DRM_CHANGE 事件。如果内容受 DRM 保护，将调度此事件。
```
player.addEventListener(MediaPlayerCapabilityChangeEvent.HAS_DRM_CHANGE, onDRMCapabilityChange);
```

在事件处理函数中，获取 DRMTrait 实例。 DRMTrait 是一个接口，通过该接口可以调用与 DRM 相关的方法，如 authenticate() 。在加载受 DRM 保护的内容时，OSMF 将执行 DRM 验证操作并调度状态事件。将 DRMEvent.DRM_STATE_CHANGE 事件处理函数添加到 DRMTrait 。

private function onDRMCapabilityChange 
    (event :MediaPlayerCapabilityChangeEvent) :void 
        { 
            if (event.type == MediaPlayerCapabilityChangeEvent.HAS_DRM_CHANGE 
                && event.enabled) 
            { 
                drmTrait = player.media.getTrait(MediaTraitType.DRM) as DRMTrait; 
                drmTrait.addEventListener 
                    (DRMEvent.DRM_STATE_CHANGE,                     onDRMStateChange); 
            } 
        }

在 onDRMStateChange() 方法中处理 DRM 事件。

        private function onDRMStateChange(event :DRMEvent) :void 
        { 
            trace ( "DRMState: ",event.drmState); 
            switch(event.drmState) 
            { 
                case DRMState.AUTHENTICATION_NEEDED: 
                    // Identity-based content 
                    var authPopup :AuthWindow = AuthWindow.create(_parentWin); 
                    authPopup.serverURL = event.serverURL; 
                    authPopup.addEventListener("dismiss", function () :void { 
                        trace ("Authentication dismissed"); 
                        if(_drmTrait != null) 
                        { 
                            //Ignore authentication. Just 
                            //try to acquire a license. 
                            _drmTrait.authenticate(null, null); 
                        } 
                    }); 
                    authPopup.addEventListener("authenticate", 
                                    function (event :AuthWindowEvent) :void { 
                        if(_drmTrait != null) 
                        { 
                            _drmTrait.authenticate(event.username, event.password); 
                        } 
                    }); 
                    authPopup.show(); 
                    break; 
                case DRMState.AUTHENTICATING: 
                    //Display any authentication message. 
                    trace("Authenticating..."); 
                    break; 
                case DRMState.AUTHENTICATION_COMPLETE: 
                    // Start to retrieve voucher and playback. 
                    // You can display the voucher information at this point. 
                    if(event.token) 
                    // You just received the authentication token. 
                    { 
                        trace("Authentication success. Token: \n", event.token); 
                    } 
                    else 
                    // You have got the voucher. 
                    { 
                        trace("DRM License:");                         
                        trace("Playback window period: ", 
                            !isNaN(event.period) ? event.period == 0 ? 
                            "<unlimited>" : event.period : "<none>"); 
                        trace("Playback window end date: ", 
                            event.endDate != null ? event.endDate : "<none>"); 
                        trace("Playback window start date: ", 
                            event.startDate != null ? event.startDate : "<none>"); 
                    } 
                    break; 
                case DRMState.AUTHENTICATION_ERROR: 
                    trace ("DRM Error:", event.mediaError.errorID + 
                        "[" + DRMErrorEventRef.getDRMErrorMnemonic 
                        (event.mediaError.errorID) + "]"); 
                    //Stop everything. 
                    player.media = null; 
                    break; 
                case DRMState.DRM_SYSTEM_UPDATING: 
                    Logger.log("Downloading DRM module..."); 
                    break; 
                case DRMState.UNINITIALIZED: 
                    break; 
            } 
        }