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If you have worked on the trackers to reduce jitter, but still need a smoother path (after checking in your animation package), you can filter the computed camera or object path using the Path Filtering dialog, launched from the Window menu or the Solver panel .
Warning : filtering the path increases the real error, and causes sliding. Remember that your objective is to produce a clean insert in the image, not produce an artificially smooth camera trajectory that works poorly.
Path filtering is legitimately useful in several difficult situations: first, in object tracking, when the object is small and may have only a few trackers; second, when there is little perspective or few or noisy trackers, such that there is ambiguity between camera position and orientation; and third, when objects must be inserted that come very close to the camera, where jitter in the solution is very visible.
The path filtering controls permit you to animate the frequency and strength of the filtering applied, and apply it selectively to only some axes. If the camera was on a dolly, you can apply it selectively to the camera height (Z or Y). For object tracking, distance filtering is often the way to go, as it is the object/camera distance that winds up with the most jitter, and that is what is filtered (or locked on the locking control panel).
When path filtering is set up, it is (and must be) re-applied after each solve, whether the solve is "from scratch" or a refine operation.
For a more subtle workflow, do the following:
Solve the shot with no filtering in place
Open the Path Filtering dialog,
Configure filtering for the translation, distance, or height axis only,
Select the "To Seed Path" option,
Click the Apply Filter Now button,
Turn off filtering on all axes,
Open the Solver Locking panel,
Turn on locks for the axes that you just filtered above,
Run a Refine solver cycle.
The advantage of this workflow is that it applies filtering to one or more axes, then gives you the best solution for the remaining, unfiltered, axes taking into account the results on the filtered axes.
The filter frequency and strength are animated parameters. When you configure filtering, you should animate the parameters to reduce filtering ( increase the frequency) at times when the path is changing rapidly, or hits actual bumps. You should increase filtering ( reduce the frequency) when the camera or object is nearly stationary, or is moving smoothly. You can animate the strength to blend in and out of filtering, or to make the filtering less effective.
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