Correcting Motion Tracking Errors

It may be necessary to adjust the tracking during an effect, as the tracking can become inaccurate when the tracked object changes orientation or is obscured by another object. The best way to deal with this is by keyframing the Track Center KF control. Final Cut Pro users need to use Linear keyframes, as Final Cut Pro doesn't support Hold keyframes.

• For detailed information on correcting motion tracking errors using Linear keyframes, see the BCC User Guide or the help file located in the Motion Tracking Parameter Group of any filter that has a Motion Tracker.
• The onscreen marks are internal to the Motion Tracker. While the Motion Tracker considers the frames represented by the blue marks to be "keyframes", these are different than the keyframes that are visible in your timeline.
• The onscreen Tracker Center KF crosshair control does not follow the tracked object, but you can reset it to the location of the tracked object at any point in the effect.

Understanding the Onscreen Tracking Marks

When Track on the Fly is enabled, a line along the bottom of the Canvas window indicates the location of tracked frames. The line references the length of the original source clip. It is important to note that this line is actually rendered onto the image in Track on the Fly mode. Turn off Track on the Fly before you render to disk or export your effect.

• A Red mark along the bottom of the window indicates the current position of the playhead.
• Blue marks indicate keyframe locations. A keyframe location is any frame whose position differs from that of the previous frame. A frame where the center position differs from the previous frame is also considered a keyframe.

Note: The blue onscreen marks are internal to the Motion Tracker. While the Motion Tracker considers these frames to be "keyframes," these are different than the Final Cut Pro keyframes.

• Green marks indicate the frames that are currently tracked (i.e. the location of the tracker center has not changed since the tracking data was generated).
• Magenta marks indicates frames which were tracked, but for which the tracker point has changed. This usually indicates a region that needs retracking (unless you are manually positioning the Tracker Center KF without making keyframes in your timeline).

Note: When you track an effect, marks for each tracked frame draw on the left of the current-time marker because there is tracking data for these frames.

Understanding Error Messages When Tracking on the Fly

The most common error message you will see during tracking is a "Please Move the Playhead..." error message.

There are several things you can do while tracking that cause this error message to appear.

• If you move forward in the effect past the end of the tracked region.
• If you don't play every frame (clicking Play instead of choosing Mark > Play > Every Frame).
• If you partly track an effect, disable Track on the Fly, and move the playhead past the tracked region before re-enabling Track on the Fly.
• This message will sometimes appear when you press the space bar to stop play. When this happens, the tracker render for the current frame is interrupted. You need to move the playhead back one frame and clear the cache to continue.

When you get this error message, perform the following steps.

1. Move the playhead to a previously tracked frame in your effect.

2. Clear the cache that Final Cut Pro has created for the effect. To clear the cache, press the Reset button then toggle a checkbox off and on, or change an unused parameter in the effect. If you try to retrack without completely clearing the cache, the motion tracker will not work when it reaches the frame that displayed the error message since that frame has already been cached.