Khalid, this is what I've done to get everything working in Mavericks.
Start with QT 7.6.6. - http://support.apple.com/kb/DL923
Get Perian, and install it. - http://perian.org
then VLC, - http://videolan.org
DivX - http://divx.com - and the
Flip4Mac package from Telestream - http://www.telestream.net/flip4mac/
This is what I've put into my system and so far I've gotten every file to run fine, even my oldest videos.
This is codecs you should see.
In System/Library/QuickTime
ApleIntermediateCodec.component
AppleMPEG2Codec.component* (*optional if you buy it)
DivX Decoder.component
Flip4Mac WMV Advanced.component
Flip4Mac WMV Export.component
Flip4Mac WMV Import.component
In your Home/Library/QuickTime/
AC3MovieImport.component
Perian.component
For AC3 sound that is in most .mkv files, you need the A52Codec.component, here:https://dl.dropboxusercontent.com/u/34821905/A52Codec.component.zip - unzip the file and put the component into the System/Library/Audio/Plug-ins/Components
Go back to your Perian settings and in the Audio Output button, set it to 'Multi Channel Sound' - Ignore the message Perian puts up and select it.
By doing a 'Get Info' on your files and where it says 'Open With' and default them to the QuickTime 7 - Perian no longer will work with QuickTime Player so you must have QT 7.6.6 and set it so it is the default for all the filetypes you use.
It should work perfectly. So far I've gotten ALL my old videos to play.
.avi, .mov (with the AC3 sound), .wmv, .flv, .mp4 and .m4v.
For web videos, make sure to go to Adobe and get FlashPlayer - http://get.adobe.com/flashplayer/
Regards,
Deb.