Problems playing higer resolution mp4 on Apple TV

[progtastic]

I am seeing playback issues with stuttering video on the Apple TV app. Most videos of a standard resolution play fine but trying to play a 720 or even 532 vertical resolution it is struggling.

I am streaming from a NAS and all is well playing higher resolution videos from the NAS with VLC on my old MacBook ( CoreDuo2 ) but trying to play the same video through the Apple TV app it cannot play and keeps stalling and is jittery.

A couple of sample of the videos encoded that play fine on the Mac VLC but not the Apple TV VLC

Codec MPEG-4 (DX50 )
Resolution 704x576
Display Resolution 700x572
Frame Rate 25
Decoded Format 4:2:0 YUV

Codec H264 MPEG-4 AVC (part10) (avc1) - I can also play this file fine on the Apple TV through iTunes home sharing ( wirelessly from my MacBook so don't think its a processor / network issue, guessing an incompatibility of the codec? )
Resolution 1280x738
Display Resolution 1280x720
Frame Rate 25
Decoded Format 4:2:0 YUV

But this (slightly ) smaller resolution plays fine on the Apple TV
MPEG-4 (XVID)
Resolution 624x532
Display Resolution 624x532
Frame Rate 25
Decoded Format 4:2:0 YUV

Is this expected/known behaviour or are there any settings I can try ( I've tried playing with the latency settings within the App but don't see many more options )

Thanks