Blender: exporting camera tracking markers to CSV

For university, I needed a camera tracker which could track motion of some particles under a microscope, and give me the coordinates of a particle for each frame. Blender has a very nice camera tracker which is ridiculously easy to use (and very fast), but it cannot export its results in a gnuplot-compatible format. But, it has a nice Python API, so you can just do it yourself! This is a script which exports all camera tracking markers of all videos in a blender file to CSV files in a directory called "data":

import bpy
D = bpy.data

for clip in D.movieclips:
    for track in clip.tracking.tracks:
        fn = 'data/tr_{0}_{1}.csv'.format(clip.name.split('.')[0], track.name)
        with open(fn, 'w') as f:
            frameno = 0
            while True:
                markerAtFrame = track.markers.find_frame(frameno)
                if not markerAtFrame:
                    break
                frameno += 1
                coords = markerAtFrame.co.xy
                f.write('{0} {1}\n'.format(coords[0], coords[1]))

Just paste this to a blender text editor window and press Alt+P to run it. You have to create a directory named "data" manually before that.

Careful: The coordinate output is in units of the video height / width. So if your video is not square sized, you need to multiply the output by the video clip dimensions (clip.size[0] and clip.size[1]).