Dissolve: Suppose We Have Video1 Dissolving into Video2, Over a Time

Essay

Dissolve: Suppose we have video1 dissolving into video2, over a time $t$ from 0 to $t_{\max }$ (video1 gradually disappears, and video2 gradually appears).
There are 2 ways that this task is commonly carried out: "Ordinary Dissolve" and "Dither Dissolve". In Ordinary Dissolve, every pixel value is changed, over time, so that it contains partly the contents of video1 and partly the contents of video2, summed additively. In Dither Dissolve, pixels are either all-video1 or all-video2, not a mix; the decision of which video to take pixel values from is based on a random number generator.
Write pseudocode solutions for accomplishing these two kinds of gradual video transition. For each type, just show the algorithm for filling up R (Red) values - Green and Blue will be similar.