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xcaplive: wearable computing/EyeTap video utility for live image recording and transmission


xcaplive is a GNU/Linux program for wearable video processing, transmission, storage, and rememberance. It is used for wearable computing and EyeTap systems, and has features specifically designed for wearable computing.


About xcaplive

When an EyeTap operates in a mode in which it is placed under computer control, a computer program is required to perform image capture from the camera display images in the aremac. To facilitate this, the author participated in the development of a program called xcaplive. Unlike most other image capture programs, xcaplive acted both as a video recorder and viewfinder (many other GNU/Linux video capture programs do not also supply a viewfinder, and many programs only display images from a video source for viewing, but do not necessarily record).

The viewfinder aspect of xcaplive was particularly important to create the illusory transparency of EyeTap. xcaplive thus took special care to provide the full dihedral group of transformations on images (the full set of symmetries of a square, i.e. rotations by multiples of pi/2, and reflections). This allowed xcaplive to be useful in a variety of EyeTap configurations, such as when the camera and aremac are rotated 90 degrees. Furthermore, images could be arbitrarily scaled and translated to allow for fine calibration of the video to ensure collinearity in EyeTap devices. Whenever possible, xcaplive utilized hardware overlay to write video directly from a capture device into the video (output) frame buffer, keeping framerates near video speeds (30fps) even for large images, reducing the latency present in the viewfinder.

It was found that one of the most useful features of xcaplive was that it was able to record EyeTap video onto a wearable computer. Image capture framerate was dependent on a number of variables, such as the desired quality, size, or amount of compression desired. The hardware worn by the user also affected frame capture speed. For instance, the camera quality and focus affected the time required to compress and write a jpeg (slightly blurred greyscale images are quicker to compress and write to jpeg format as compared to full color images with sharp edges). Of course, the processing speed of the wearable computer was critical. Since NTSC has a framerate of 30 frames per second (fps) , and many video sources, such as cameras, do not go past 30fps at any resolution, 30fps was a logical maximum desired framerate for video capture. In cases where 30fps was not possible, however, motion between frames could be interpolated to effectively upsample the image sequence to 30fps.

xcaplive further provided a platform upon which to experiment with other uses of computer mediated EyeTap. One such use is the live wireless transmission of images to the internet, creating a "wearable wireless webcam". This has its origins in the early usage of wearable computers as roving reporters, where wearable computers were found to have uses in news gathering.