/*
 * call-seq:
 *   snapshot() -> Array
 *
 * Grabs the current frame from the video. On success, returns an Array of
 * Arrays of scanlines.  Each scanline array is filles filles with pixel data
 * as fixnums between 0 and 255 and in the following pattern: [ r, g, b, r, g, b,
 * ... ].
 */
static VALUE xs_get_snapshot(VALUE self) {