What kind of video are you trying to play? As far as I know, the only videos that the native player can't play but that can be played on the playbook is flash, and there are a couple of cheap apps in app world that exclusively play flash.
i want to play avi, mkv mp4 but on some video i can not hear the audio... any solution
You best stick with video that have mp3 or acc audio components. Either Gspot (not what it sounds like) or MediaInfo can show the contents of the video to check the audio components.