i have tried many settings and players but the result is same. i googled it a lot and found out that this problem exists with many HTC phones.
i have found few interesting things:--
1.) if you convert an existing .mp4 video file for your phone, then audio will play in sync with video. But if you convert video having a different format than .mp4 then u ll have this problem.
2.) Convert your videos to .divx and use Yxplayer. You ll not have any audio sync problems. You can use any converter to convert into .divx.
Currently im using YXplayer for playing my videos. I know this is a paid app, but currently we dont have any choice.
HTC should fix this probelm ASAP. Otherwise there is no point of having a smartphone.