+ \item[Motion settling speed] The motion detected between every frame can be accumulated to form an absolute motion vector. Settling speed determines how fast the accumulated translation fades away, and the image resettles to its actual appearance. If the settling speed is 0\% the total absolute vector is added to the next frame. So every frame that is processed accumulates the whole motion of the past. If the settling speed is 100\% the absolute vector is cancelled completely, adding no past translation to the next frame. If the settling speed is intermediate between 0\% and 100\% the absolute vector is downscaled by (100 $-$ settling amount) before being added to the next frame.
+ \item[Track rotation] Enables rotation operations. The motion tracker tracks rotation in the \textit{master} layer and adjusts rotation in the \textit{target} layer.
+ \item[Rotation search radius] This is the maximum angle of rotation from the starting frame the rotation scanner can detect. The rotation scan is from this angle counterclockwise to this angle clockwise. Thus the \textit{Rotation search radius} is half the total range scanned.
+ \item[Rotation search steps] Ideally every possible angle would be tested to get the rotation. To speed up the rotation search, the \textit{Rotation search radius} is divided into a finite number of angles and only those angles compared to the starting frame. Then the search radius is narrowed and an equal number of angles is compared in the smaller radius until the highest possible accuracy is achieved. Normally you need one search step for every degree scanned. Since the rotation scanner scans the \textit{Rotation search radius} in two directions, you need two steps for every degree in the search radius to search the complete range.
+ \item[Rotation center] Usually this parameter is zero, and the rotation search
+ range is $+/-$ \textit{Rotation search radius}. Otherwise, it shifts the rotation search range to the area of angles between (\textit{Rotation center} $-$ \textit{Rotation search radius}) and (\textit{Rotation center} $+$ \textit{Rotation search radius}).
+ \item[Maximum angle offset] The total accumulated amount of rotation is unlimited
+ if this is 90 degrees. If it is under 90, the total amount of rotation is
+ limited by the given maximum angle.
+ \item[Rotation settling speed] This parameter determines how fast the accumulated
+ rotation fades away. Analogously to the \textit{Motion settling speed}, if it is 0\%,
+ the total accumulated rotation is added to the next frame, and every frame
+ accumulates the whole rotation of the past. If the settling speed is 100\%,
+ no past rotation is added to the next frame. If the settling speed is
+ intermediate between 0\% and 100\%, the amount of accumulated rotation is
+ downscaled by (100 $-$ settling amount) before being added to the next frame.
+ \item[Motion noise level] This parameter allows to compensate such undesirable
+ behavior when motion tracker wildly springs away because some outlying area
+ of a noisy picture becomes accidentally more "similar" to the reference
+ picture than the right one. If noise level is set to 0\% (its normal value),
+ then it is not taken into account at all. When it is set to 100\%, then
+ similarity of the match block contents is totally ignored, and the current
+ motion vector will be zero. An intermediate value between 0\% and 100\%
+ defines the proportional noise level between minimum and maximum difference
+ of all examined match block positions. From all such positions whose
+ difference is found below noise level, that one is chosen which has the
+ shortest translation relative to the reference frame.
+ \item[Rotation noise level] This parameter has similar meaning to the \textit{Motion noise level}. It influences rotation tracking. If set to 0\% (its normal value),
+ it is not taken into account. The 100\% setting completely suppresses
+ rotation detection. An intermediate value between 0\% and 100\% defines the
+ proportional noise level between minimum and maximum difference of all
+ examined rotated match blocks from that of the reference picture. From all
+ rotation angles whose match block differences are found below noise level,
+ that one is chosen which has the minimum rotation angle relative to the
+ reference frame.
+ \item[Draw vectors] When translation is enabled, $2$ boxes are drawn on the frame. One box represents the translation block. Another box outside the translation block represents the extent of the \textit{Translation search radius}. In the center of these boxes is an arrow showing the translation between the $2$ master frames. When rotation is enabled, a single box the size of the rotation block is drawn rotated by the amount of rotation detected.
+ \item[Two pass tracking] Although this parameter can be enabled at any time, it is useful only while simultaneous tracking both translation and rotation, when
+ the rotation amount is large. The normal tracking algorithm firstly
+ examines translation, then rotation. However, comparison of a strongly
+ tilted picture with the reference one can lead to rather inaccurate
+ determination of the translation vector. The subsequent determination of
+ rotation will be also inexact because of the preceding translation error. The
+ second tracking pass, if enabled, refines translation and rotation.
+
+ If motion and/or rotation noise level is set above 0\% and \textit{Two pass tracking}
+ is enabled, then both noise levels affect the first tracking pass only.
+ During the second tracking pass of two pass tracking both noise levels are
+ ignored.
+
+ It should be noted that two pass tracking is not twice slower than the usual
+ single pass tracking. Actually it is only about 40\% slower. As the second
+ pass serves only for motion refinement, it starts from the reduced search
+ range for block positions and rotation angles. And, as the first pass only
+ yields an approximate position, which will be later refined during the
+ second pass, it skips subpixel position search and examines rotation angles
+ with the accuracy reduced to 1 degree.
+ \item[Track single frame] When this option is used the motion between a single
+ starting frame and the frame currently under the insertion point is
+ calculated. The starting frame is specified in the \textit{Frame number} box. The
+ motion calculated this way is taken as the absolute motion vector. The
+ absolute motion vector for each frame replaces the absolute motion vector
+ for the previous frame. \textit{Settling speed} has no effect on it since it does
+ not contain any previous motion vectors. Playback can start anywhere on the
+ timeline since there is no dependence on previous results. We talk about
+ \textit{Keep shape} and it is the most precise way to calculate the motion vector;
+ but it only works well when the object to be traced does not change along
+ the clip, remaining identical in shape, size and luminance.
+
+ Strong rotation of the picture can also have a bad impact on the tracking
+ accuracy. If it is the case, accuracy can be significantly improved by
+ enabling \textit{Two pass tracking}.
+
+ \item[Frame number] The number of the reference frame used for motion tracking in
+ the \textit{Track single frame} mode is specified in this input field. Frame
+ number is set as the 0-based absolute number starting from the very
+ beginning of the whole timeline. Instead of manual calculating, it is
+ possible to get \textit{Frame number} directly from the current cursor position by
+ pressing the \textit{Get current} button.
+
+ \item[Get current] Pressing this handy button provides a convenient way to set the
+ \textit{Frame number} parameter to the value of the current cursor position.
+
+ \item[Add (loaded) offset from tracked frame] This toggle can help when the tracked
+ object changes shape, leaves the screen area or becomes obscured by other
+ objects somewhere in the middle of the \textit{Motion} effect. Sometimes it can help
+ also if a strong rotation causes the motion tracker to miss the right
+ tracked object and wildly spring away.
+
+ To overcome this problem, one has to define two keyframes: the first one at
+ the start of the \textit{Motion} effect, the second shortly before the problematic
+ location in the clip. At the first keyframe one defines the \textit{Motion} effect
+ parameters as usual, the \textit{Add offset} toggle being switched off. At the
+ second keyframe the match block can be redefined to cover another region of
+ the picture which remains visible during the following part of the effect.
+ The \textit{Frame number} parameter should be set several frames before position of this second keyframe, and the \textit{Add offset} toggle switched on.
+
+ After defining the two keyframes (even more can be added in the similar way)
+ one switches at all the defined keyframes \textit{Calculation} mode to \textit{Save coords
+ to tracking file}, \textit{Action} mode to \textit{Do Nothing}, rewinds the timeline cursor
+ to the beginning of the \textit{Motion} effect, and starts playback. The determined
+ motion vectors will be written to the tracking file, the \textit{Add offset}
+ parameter having no effect during the \textit{save} stage.
+
+ After playback finishes and all the relevant motion vectors are saved in the
+ tracking file, one switches at all the defined keyframes \textit{Calculation} mode to
+ \textit{Load coords from tracking file}, \textit{Action} mode to whatever one needs, rewinds again to the beginning of the \textit{Motion} effect and starts playback or
+ rendering. After reaching the second keyframe, where \textit{Add offset} was
+ switched on, the program continues to follow the second object adding the
+ total motion and rotation, accumulated so far.
+
+ Of course, the \textit{Add offset} toggle can be used in the \textit{Track single frame} mode only. In the other tracking modi such a technics is unnecessary.
+ \item[Track previous frame] Causes only the motion between the previous frame and
+ the current frame to be calculated (\textit{Follow shape}). This is added to an
+ absolute motion vector to get the new motion from the start of the sequence
+ to the current position. After every frame processed this way, the block
+ position is shifted to always cover the same region of the image. Playback
+ must be started from the start of the \textit{Motion} effect in order to accumulate
+ all the necessary motion vectors. This method is less precise because you
+ have error propagation between frames. However, it is essential when the
+ object changes shape, size or luminance. Possible inaccuracies caused by
+ rotation of the picture can partly be reduced by enabling \textit{Two pass tracking}
+ \item[Previous frame same block] This is useful for stabilizing jerky camcorder footage. In this mode the motion between the previous frame and the current frame is calculated. Instead of adjusting the block position to reflect the new location of the image, like \textit{Track Previous Frame} does, the block position is unchanged between each frame. Thus a new region is compared for each frame.
+ \item[Master layer] This determines the track which supplies the frames for the
+ motion calculation. If it is \textit{Bottom} the bottom track of all the tracks
+ sharing this effect is the \textit{master} layer. Then the top track of all the
+ tracks is the \textit{target} layer. And vice versa, if the \textit{master} layer is \textit{Top},
+ then the \textit{target} layer is bottom.
+ \item[Calculation] This determines whether to calculate the motion at all and
+ whether to save it to disk. If it is \textit{Don't Calculate} the motion calculation is skipped. If it is \textit{Recalculate} the motion calculation is performed every time each frame is rendered. If it is \textit{Load coords from tracking file}, the motion vectors are loaded from a previous \textit{save} calculation. If the previous \textit{save} calculation does not provide the data for the currently processed frames, a new motion calculation is performed for that frames. If \textit{Calculation} mode is \textit{Save coords to tracking file} the motion vectors can be still loaded from disk if the previously
+ calculated data exist. Otherwise, a new motion calculation is performed,
+ and the calculated motion vectors are saved.
+ \item[Tracking file] This parameter determines the name of the file where the
+ motion data are saved and/or loaded from. By default it is \texttt{/tmp/motion}
+ but it can have any name and reside anywhere on the disk. \textit{Tracking file} is
+ a text file where each line contains four numbers: the absolute frame number
+ (0-based integer), the X and Y translation displacements of subpixel
+ precision (a subpixel is $\frac{1}{4}$ pixel in size, and to give integer values of X and Y these subpixel coords are multiplied by 4), and the rotation angle in
+ degrees (as a floating point value). The user may have different tracking
+ files for different timeline regions, it is possible to do any manipulations
+ on them if necessary and even manually edit in a text editor.
+ \item[Generate tracking file name] This handy pushbutton suggests a tracking file
+ name based on the name of the current asset. It helps to maintain more
+ different tracking files with unique but predictable names used in the same
+ project. When tracking file name is changed (either via the pushbutton or
+ after entering it in the corresponding input field), the contents of that
+ files (both the old and the new ones) remains unchanged.
+ \item[Clear tracking file contents] The values and meaning of the saved motion data depend on such a bunch of parameters, they can be even edited manually, so
+ one can hardly predict whether the outdated motion vectors are to be reset
+ or left untouched. Therefore the existing motion data are never altered
+ implicitly (only newly calculated data may be added). And, should the user
+ need to reset them here and right now, it is possible to clear the given
+ tracking file contents explicitly by pressing this pushbutton.
+
+ As protection against accident clearing tracking file contents, right before
+ clearing the program ensures closing the current tracking file and renames
+ it to the same name with the suffix \texttt{.old}. This way, the user can undo an erroneous clearing action by manual restoring the saved file.
+ \item[Action] Once the motion vector is known this determines whether to move the \textit{target} layer opposing the motion vector or following the motion vector. If it is \textit{Do Nothing} the \textit{target} layer is untouched. If it is \textit{Track\dots} the \textit{target} layer is moved by the same amount as the \textit{master} layer. This is useful for matching titles to objects in the frame. If it is \textit{Stabilize\dots} the \textit{target} layer is moved opposite to the motion vector. This is useful for stabilizing an object in the frame. The \textit{Motion} operations can be accurate to single pixels or subpixels by changing the \textit{Action} setting.