I've seen a number of posts already talking about the Intensity Pro/Shuttle's "gradual video-audio out of sync" issue. As a sufferer as well, I dug into the problem and found the "true" cause of the problem:
As the capturing goes, the Intensity constantly and randomly creates "redundant" frames for the video (like 0.x second tiny loops), which cumulatively makes the video length longer then it should be. The audio length is correct. For example, if the final clip should be 1:00:00 long, the video length may be 1:03:24 and the audio length is 1:00:00. This looks very much like a "sync" issue but actually it is not. The video footage is inaccurate.
I also tried different codec for capturing. Surprisingly, the MJPEG codec causes more "redundancy" than 8-bit and 10-bit uncompressed ones. So I believe it has very little, if there is some, to do with the PC spec rather than the codec itself.
In terms of the compatibility issues among the codecs installed on the computer, I clean installed the Windows 7 64-bit OS with necessary drivers only, and the problem is still there. One thing worth mentioning: If I get the "old" directx 9.0c (which is not integrated in the Windows 7 system) installed, the problem will be much less notable. For a hour-long clip, the redundancy simply drops from 10+ seconds to one or two seconds, but still noticeable.
These are all that I found out, does anyone has a clue how to fix it? Much appreciated.
I'm also suffering from the audio being out of sync with Intensity Shuttle.
Whenever I take the video file into Vegas for editing, it's always shorter than the actual video as said above.
Changing the codec between MJPEG or 8-bit / 10-bit YUV somewhat affects the video, but it's usually still more or less out of sync. Stretching the audio in the Sony Vegas sometimes work (mostly it doesn't), but even those times that it works, it makes the audio being out of sync in the beginning of the video.
I tried once to record in 480p for little less than one hour, which seemed to fix the problem with audio but while in 720p or 1080i the audio is always out of sync after ~20 minutes of recording.