About User Experience, Firefox 3.1 is going to be a minor release. But about
standards and performance, it's a great step forward.
Check out the new features you can use in your web page: Firefox 3.1 for
developers.
I've created a little demo using the video element,
canvas, DOM Workers (threads in
JS) and a few Javascript 1.7/1.8 tips. It's
a movement tracker. It's not perfect, but it's fun :)
Movement tracker: http://people.mozilla.com/~prouget/...,
click on the Go button (Firefox3.1
needed).
How does it work ?
For each frame:
- First, I compute the difference between the frame n and the frame
n - 1 (greyscale);
- then (in the Worker), I do a matrix convolution to detect pixel moving (you
can choose between 3 kind of matrix: Sobel, Harris and
Kirsch);
- From the result, I compute the bounding box containing moving pixels (rects
displayed in the video) and the centroid of the moving pixels (crosses inside
the rects);
- There is a bounding box and a centroid for the x movements (color
red) and for y movements (color green);
- The evolution of the weight of each centroid is displayed in the
graph;
The arguments:
- Threshold: when a moving pixel should be ignored;
- Work factor: we don't need to compute the entire frame. We can reduce
it;
- Zoom factor: the resulting video is not a <video/>, but a canvas.
Define the ratio between the canvas size and the original video size;
- Sensibility: when a global movement should be ignored. Size of the bounding
box;
- Display video: display the original <video/> element;
- Display diff: display the diff frames;
It's a really quick&dirty implementation, if I have time (or you, if you
have some time), I think a good enhancement would be to implement the camshift
algorithm to track objects.
