I am tracking motions with blender, and adding motion trails to tracked objects. With hq slow motion footage, just attaching an empty vert with a particle effect to my track works very well. However, when the frame rate is not very high, the tracker will be quite far apart frame to frame and I end up with what looks like a dotted line because the emitter jumps from one tracker location to the next. I would like to bridge the gap either with more particles or just a line. How can I distribute more particles between the current and previous/next tracker location? Maybe I have to convert the track into a path or a line (I can't figure out how)? Basically what i want to achieve is a smooth gap-less motion trail even when the tracked object moves quite a bit between frames. Grateful for any advice, thank you.
You can do this with Animall (Addon, has lots of presets), but I always found it a bit wonky and it's not really migrated to 2.8 yet. With a little more effort you can use Animation Nodes for that, in the end you have way more control over the behaviour of your path. Here's a screenshot of my Nodetree, note that the dotted line is just the visualized motion path of the empty, the selected curve is the actual offset. I moved it to the side, so you can distinguish between them.
You can probably clean the tree, or not use a loop, but this way works. Note that if you have more than just location keyframes on your object, the list indices might change.
Tracking information creates a constraint.
To convert constraints into keyframes, open the constraint section of the properties window and press Constraint to f-Curve
The tracking information will be converted to keyframes, the curves for those keyframes can be displayed and manipulated on the Graph Editor.
There are a few built in tools to clean up curves in the key menu of the Graph Editor.
Here's the same motion path after applying the "Clean Keyframes" function: