import numpy
from os import devnull
from random import randrange, uniform
from subprocess import Popen, PIPE

width = 640
height = 360
boxsize = height / 8
quality = 18.0                  # 0 - 51, smaller = higher bitrate
framerate = '30000:1001'        # 29.97 fps (NTSC)
numframes = 900
outfilename = '20120419.mp4'

def rectangle(frame, top, left, w, h, Y, P):
    top, left, bot, right = map(lambda x: int(round(x)), (top, left, top + h, left + w))
    frame[0, top:bot, left:right] = round(Y * 219 + 16)         # Y' [0, 1] -> Y' [16, 235]
    frame[1, top:bot, left:right] = round(P[0] * 224 + 128)     # Pb [-0.5, 0.5] -> Cb [16, 240]
    frame[2, top:bot, left:right] = round(P[1] * 224 + 128)     # Pr [-0.5, 0.5] -> Cr [16, 240]

def bouncing(min, max, delta, callback=None):
    val = uniform(min, max)
    while True:
        yield val
        val += delta
        if val < min or val > max:
            val = 2 * min - val if val < min else 2 * max - val
            delta *= -1
            if callback:
                callback()

class Randomchroma(object):
    def __init__(self): self.picknew()
    def picknew(self):  self.val = uniform(-0.5, 0.5), uniform(-0.5, 0.5)

frame = numpy.zeros((3, height, width), dtype=numpy.uint8)
chroma = Randomchroma()
luma = bouncing(0.15, 0.9, 0.033)
x = bouncing(0, width - boxsize, uniform(height / 200, height / 20), lambda: chroma.picknew())
y = bouncing(0, height - boxsize, uniform(height / 200, height / 20), lambda: chroma.picknew())

ffmpeg = Popen('ffmpeg -y -f yuv4mpegpipe -i - -vcodec libx264 -profile high -level 5 -x264opts crf={0} {1}'
               .format(quality, outfilename).split(), stdin=PIPE, stdout=open(devnull), stderr=open(devnull))
ffmpeg.stdin.write('YUV4MPEG2 W%d H%d F%s Ip A0:0 C444\n' % (width, height, framerate))

for f in xrange(numframes):
    rectangle(frame, 0, 0, width, height, 0, (0, 0))
    rectangle(frame, next(y), next(x), boxsize, boxsize, next(luma), chroma.val)
    ffmpeg.stdin.write('FRAME\n')
    ffmpeg.stdin.write(frame.tostring())

ffmpeg.stdin.close()
ffmpeg.communicate()