import gst, time

p = gst.parse_launch("videotestsrc ! videomaxrate ! videoscale ! ffmpegcolorspace ! capsfilter name=c ! fakesink");

c = p.get_by_name("c")
assert p.set_state(gst.STATE_PLAYING) != gst.STATE_CHANGE_FAILURE
i = 1
b = p.get_bus()

while True:
    time.sleep(1)
    capsstr = "video/x-raw-yuv, width=320, height=240, framerate="+str(i)+"/1"
    print("caps: " + capsstr)
    c.set_property("caps", gst.caps_from_string(capsstr))
    i += 1
    if (i > 30):
        i = 1
    while True:
        msg = b.pop()
        if not msg:
            break
        if msg.type == gst.MESSAGE_ERROR:
            print "YO"