PLaying Video in Background in wp8 - windows-phone-7

Question

I am developing an app for Wp7.x and Wp8 which runs YouTube Video with lock screen disabled.
I have seen that new version of MyTube App and Microsoft version of your tube app which has been pulled back had a feature which allows user to keep listening to Video(Audio part) when phone is locked via lock screen. I want to Develop a YouTube Radio type of app which keeps pulling new Specific type of Viedo Url from youTube site and play the audio part even if running in background or In a Locked screen.
See MyTube App in wp8 store to know more what I am talking about.

Answer 1

The Windows Phone application goes to dormant/tombstone mode when the phone screen is locked. This behavior can be altered by changing the properties UserIdleDetectionMode and ApplicationIdleDetectionMode of PhoneApplicationService class. By default UserIdleDetectionMode and ApplicationIdleDetectionMode are set to Enable, which allows the service to lock the phone when the user is idle and these deactivate the application when the phone is locked.
As shown below, I have used ApplicationIdleDetectionMode, which when set to Disable doesn't deactivate the application when the phone is locked.
PhoneApplicationService.Current.ApplicationIdleDetectionMode = IdleDetectionMode.Disabled;
PhoneApplicationFrame rootFrame = App.Current.RootVisual as PhoneApplicationFrame;
if (rootFrame != null)
{
rootFrame.Obscured += new EventHandler<ObscuredEventArgs>(rootFrame_Obscured);
rootFrame.Unobscured += new EventHandler(rootFrame_Unobscured);
}
Once ApplicationIdleDetectionMode is Disabled, it cannot be Enabled until the application is re-launched. If you try to enable it, it will throw an exception. To handle the locking and unlocking state of the device you can call the Obscured and Unobscured event handler of RootFrame. Obscured will be called when the phone is getting locked. Here we should use minimum CPU, less battery consumption etc. and Unobscured gets called when the phone is getting unlocked. This is the stage when we can resume all the states of the application.

Answer 2

In Windows Phone 8, you can actually give video URLs to the BackgroundAudioPlayer class and it will play them in the background. I use this technique in Podcaster to switch between audio and video, though it's a user interaction that triggers the switch.
Updated
In Windows Phone 7 this technique doesn't work. Furthermore, MediaElement will always pause video when the lock screen is shown (even if ApplicationIdleDetectionMode is disabled) and there's nothing you can do about it.
In short, you can work around it in WP8 but there's nothing you can do on WP7