which additioal software is needed for downloaded movies that won't play on OSX 10

[Misneach6]

I can't figure out which additioal software is needed for downloaded movies that won't play on my OSX 10.6.8. I presume I have all the automatic updates but it will only play mp4s.
For .avi files I get "movie can't be opened. May need to install additional software" OR "movie not in a format that Quick Time Player understands".
For .mkv files I get "Error Dolby Audio, player does not recognise the audio in this video".
My TV has no problem playing all of these files.
Any ideas?

 

[Bruno09]

Hi,

you might use VLC, for example, or MplayerX (App Store).

 

[Misneach6]

WOW it works, thanks Bruno9, much appreciated