I think you are going to have to purchase the AVCHD codec, however before you do can you run GSpot again on a video clip and then click the 1,2,3 buttons below MS A/V in the bottom left corner of the GSpot window as shown in the image below - if this fails then the codecs are not installed.
That means you are missing the correct codec for the video files.
Should have asked earlier - what is the source of the files?
If a camera (still or video), did it come with some software to install? You may find that the camera is using a custom codec which needs installing.
One of my pet hates is when a camera manufacturer states they use a standard codec eg H.264 or MOV, only to find it is customised and you have to install their software to be able to use the video clips.
The source of the files are from a panasonic lumix fz100 bridge type camera.
Initially I had the video record settings set to avchd and these files worked correctly once I purchased the avchd codec. I then changed the setting to .mov and took the rest of the videos and stills whilst on holiday.
During that time I found that I did not get on with the camera and subsequently sold it on my return, so I have no panasonic software that I can use.
I have since purchased a canon camera, their video clips seem to work without special cocecs.