Hi guys ive seen loads of posts on this site about poor 720/1080p playback in recent ubuntu versions I had this problem and fixed it so I thought id share it with everyone....

1 install mplayer

2 install smplayer frontend {in software center}

3 open smplayer

4 go to "OPTIONS" then "PREFRENCES" then "GENRAL"

5 if you have a nvidia card choose "OUTPUT DRIVER" and select "VDPAU" {for ATI or AMD choose xv (0 - ATI Radeon AVIVO video) I dont know if this will work as my card is nvidia but it should)

6 go to performance on the left hand side and set both local and streaming cache to 99999 (this may also fix dvd playback if you set that cache aswell}

7 check the box for "ALLOW HARD FRAME DROP" and set "LOOP FILTER" to skip only on HD

8 Set the "THREDS FOR DECODING OPTION TO THE NUMBER OF CORES YOUR CPU HAS IF YOU HAVE MORE THAN ONE CPU ADD UP ALL THE CORES FOR BEST PERFORMANCE"

9 Enjoy you HD movies again on ubuntu......

I have a pretty avrage machine heres my spec....

2x Pentium 4 ht 3 ghz

Stock dell power and motherboard

GFORCE 310 HDMI

24 inch full HD tv as a monitor

so any one with dule core cpu should have no problems getting this to work.

hope this helps someone out.