WD Mybook Live supports DLNA, however which player in iPad supports this video streaming mode?
Try AirPlayer from App Store or from apptrackr.org
I don’t think Apple supports DLNA, but you can always use BuzzPlayer HD from the App Store like I do. It plays any video up to 720p mkv and you don’t need to run the PC or Mac. But you can always use AirVideo, if you leave the PC/Mac open.
Use the pair servetome/streamtome from the app store.
servetome will have to be downloaded from the author, it works with macs and pcs
These apps do transcoding on the fly and support subtitles.
If you have an apple tv2 you can have streamtome iPad app send the video/audio
to your TV
You will need to mount the NAS on the mac/pc that is running servetome and
tell servetome to use the NAS.
It works great!