I think, I haven't looked at their implementation; they'll be an artifact of piping the encrypted/mis-decrypted stream into a video decoder. A lot of video codi

I think, I haven't looked at their implementation; they'll be an artifact of piping the encrypted/mis-decrypted stream into a video decoder. A lot of video coding techniques use variable-size blocks to describe changes to areas of the image, so it's reasonable that piping pseudo-random data into the decoder would produce some noticeable block shapes.