I have giving up on the WD TV Live Streaming device. My whole library is MP4 and the device can not play them. I have 3 different devices all work, including a WD TV HD LIVE.
I have recommended to friends and family not to purchase this device. It is sad that WD would release a device that can not play the same files as previous WDTV devices.
Other than the network error I’ve documented with MKVs, I find that MKV is by far the most “reliable” format on the WD given its multiple different combinations of Video / Audio support.
MP4s have SEVERAL issues:
1- VOBSUB subtitles make the screen flash.
2- Secondary audio tracks aren’t accessible.
3- AAC audio in MP4 is often out of sync.
I feel your pain; I have a handful of MP4s / M4Vs left over for testing, but I generally also convert them over to MKV…