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In the tracker settings panel, I can choose options like pattern size and search size, but below the search size, I see: "Tracker:", with no option to choose from. Under that line, I see "Motion model:" with some options to choose.

I'm hoping to get better tracking using "hybrid", but I just can set that option. Any suggestion what happened to it?

Note: using blender 2.68a (2.68.0 r58537) on Win7.

Missing tracker dropdown - highlighter by red arrow

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This option was removed in 2.64:

First, the old option called Tracker was eliminated. The old Hybrid tracker was doing exactly the same as the SAD tracker, with the exception that it could do more accurate subpixel precision tracking by following the brute-force search with a subpixel refinement. The SAD tracker was also limited in that it only worked on 8-bit images and is unsuitable for 32-bit float images like those used in Mango.

Secondly, the KLT tracker with its pyramid tracking helped tracking blurry footage, but could be quite useless when the background texture was moving in the opposite direction of the feature point. In such cases the Hybrid tracker was much better than KLT, and for this reason the KLT tracker was made obsolete.

In other words, the SAD and KLT options were replaced with a improved hybrid tracker with new options.

From the wiki:

The new tracker is a unified algorithm with more options, and specifically some options to make it work exactly the same as the old non-planar Hybrid tracker. The options are:

  • Motion Model defines which possible motions tracking feature has. Currently supported models are: Location only, Location+Rotation, Location+Scale, Location+Rotation+Scale, Affine and Perspective. This option should be set depending on which motion a particular feature has and it'll make tracking most accurate for such a motion. Perspective is usually used to track a planar feature, but often Affine is a good enough approximation and may have more stable tracks.
  • Prepass enables a two pass tracking, where the first pass is a brute force tracking of location only, and the second pass will use tracking of the full motion model refining the first pass. To get behavior that is almost identical to the Hybrid tracker in previous Blender versions, enable Prepass and set the motion model to Location only.
  • Normalize means patterns will be normalized by their average intensity while tracking, to make them invariant to illumination changes. An example where this is useful is a scene where a marker moves in the shadow of an actress. Previously it would not be possible to track such a situation, scale adaption would shrink the area to compensate for the change in illumination, losing the track. With "Normalize" turned on, the patch is correctly tracked and scale is maintained.
  • Correlation is now a single value for all tracking settings and defines the minimal correlation between a matched pattern and a reference to be considered a successful tracking. If the tracker is giving up too easily, decrease this value, or if the tracker is slipping too much when it should give up sooner, increase this value.

Note that it is possible to simulate the old Hybrid tracker with the current method:

To get behavior that is almost identical to the Hybrid tracker in previous Blender versions, enable Prepass and set the motion model to Location only.

E.g:

enter image description here

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