can not understand transition some code. Help,thanks

[vangogh0318]

I don't understand the code below. I have two question

1.why do this operation : x[0, -1] = imgs[0]
imgs[0] Represents actual number of frames?
I think that imgs[0] is the first predicted frame by T(transition) function, why Assign imgs[0] to x[0,-1]

2. What does this operation mean?
   what's the different between video[:, 0] and video[:,1]
   video = video.reshape((batch_size, 2, 80, 160, 3))
   return video[:, 0], video[:, 1]

here is code : --------------------------

    def sampler(z, x):
            video = np.zeros((128, 80, 160, 3))
            print "Sampling..."
            for i in range(128):
                    print i
                    x = x.reshape((-1, 80, 160, 3))
        
                    code = sess.run([E(I)[0]], feed_dict={I: x, K.learning_phase(): 1})[0]
                    code = code.reshape((batch_size, time+out_leng, z_dim))
                    inp = code[:, :time]
                    outs = T.predict(inp, batch_size=batch_size)
                    # imgs = G.predict(out, batch_size=batch_size)
                    imgs = sess.run([G_dec], feed_dict={out: outs, K.learning_phase(): 1})[0]
                    video[i] = imgs[0]
                    x = x.reshape((batch_size, time+out_leng, 80, 160, 3))
                    x[0, :-1] = x[0, 1:]
                    x[0, -1] = imgs[0]

           video = video.reshape((batch_size, 2, 80, 160, 3))
           return video[:, 0], video[:, 1]