Problem Playing .3gp Video Files

My HTC HD phone produces video files in .3gp format. Soon after acquiring it I took some clips in portrait mode. When I went to store them on my Windows 7 Vaio I did wonder whether Windows Media Player would handle portrait videos, but it was no problem.

However, WMP suddenly recognises new portrait clips only as sound recordings. I have not changed any settings; indeed, the clips already stored on the laptop still play properly. But the really baffling thing is that fresh clips are still recognised as videos if taken in landscape mode.

The results are the same whether I transfer via USB or Bluetooth.

Any ideas or advice would be welcome.

For anyone interested I've found the answer. The HTC HD has several video quality settings. Using any of them except the highest produces clips that WMP can handle in either portrait or landscape orientation. But if the highest resolution [HD 720P (1280 x 720)] is chosen WMP will not recognise video captured in portrait, so landscape must be used.

It's a mystery to me why this should be, particularly as the VLC player does not have this problem. It would be helpful if anyone knows if any WMP settings need to be changed.