Don't download codecs!!!
Use the codec your camera used when shooting and export to the format you need.
Read Bill Hunt on a file type as WRAPPER http://forums.adobe.com/thread/440037
What is a CODEC... a Primer http://forums.adobe.com/thread/546811
What CODEC is INSIDE that file? http://forums.adobe.com/thread/440037
Report back with the codec details of your file, use the programs below... a screen shot works well to SHOW people what you are doing
For Mac http://mediainfo.massanti.com/
See 2nd post for picture of NEW ITEM process http://forums.adobe.com/thread/872666