I found this older thread and thought I would post this here to help people out, since I was having the same exact problem with 64 bit Sonar. My clients keep sending me mov and mp4 files, and previously I had to do conversions. Now I can import the mov files directly without issue. Here is my repost from another topic:
I am posting this here as a helpful tip for anyone trying to get HD video to either a) import properly into Sonar 64 bit, or b) play smoothly and in sync once it does import. There are a great number of crappy free codec "solutions" out there that can do more harm than good. I am working on a (non-film scoring) project with a company that actually masters consumer Blu-ray content, and they sent me a link to a codec download that totally solved my problems getting HD video to play properly within 64 bit Sonar. When I was researching how to solve this problem, it seemed like many others out there were having the same issues (unable to import video, horrible playback), so I thought I would share the solution I found here.
To find the specific pack I downloaded, Google "google lav filters 0.58.2" with the word "google" actually in the search window. That brings you directly to a safe download that does not try to install other software along with the filters. You can just Google LAV filters and find other versions; all I know is that this version worked perfectly for me. I am now able to import .mov, .mp4 and avi files that use H264 without any problems.