Not all shots will successfully camera track. Sometimes you can delete the tracking markers that attach to a person in the shot and it will successfully resolve. Other times you need to roto your person out of the scene and pre-compose. The technique depends entirely on the shot. Camera tracking relies on fixed geometry moving in the shot and anything that covers it up or adds confusing data fouls it up.
If you post the shot we might be able to suggest a technique that would work.
It tracked fine. when i try pairing the null to a seperate object it doesnt work. But when i create a solid or text layer from the track they are locked in to the track as they should be. I assumed you just parent anything else to the null but instead what im pairing (a mov file) moves with a person who is moving in the shot. Maybe its a glitch?
This does not sound like a glitch, it sounds like user error caused by little misunderstanding of how camera tracking works. The only thing the camera tracker adds keyframes to is the camera. It calculates the angle of view, camera position and camera movement. When you pick markers they need to be in the same plane as the object in the scene. For example, if you had some tracking markers on an object that was 4 feet in front of the camera and some other markers on an object that was 20 feet from the camera and you used this markers to add a solid and a camera the solid would not stick to either object in the scene, it would float between them and probably look a little odd. You also have to be careful of lens distortion because AE's camera is perfect. Camera tracking a GoPro without fisheye removed may give you a good track in the center of the frame but as the objects move to the edge the track will fail because of the lens distortion. For any shots with a lot of lens distortion you have to remove it first, pre-compose or render a DI (digital intermediate) and then camera track the fixed footage.
There is no difference between adding a null or adding a text layer or solid. If you have chosen and positioned your target well a 3D layer will be added to the scene and it will stick to the surface you have chosen. Parenting something to a null or anything else added to the scene with the Camera Tracker will not put that object in the right place in the scene. The only real use of parenting when you are setting up your scene would be to add a new 3D layer then hold down the shift key while you parent it to the placed layer (your null) so that it would snap into the right position in 3D space. If you wanted to move it in the scene you would have to move it in X Y or Z space to the new position keeping in mind the positioning of the layer as if it were in front of the camera.
I hope this helps.
Got it. Thanks!