There is a difference between mirrors or live video and a recording. After the desire or passion has died down, one may have a more critical eye when viewing a recorded session later and flaws may be noticeable: distracting background, lighting, camera angle, etc.
I seldom use a mirror since I prefer a blindfold. However, it does seem like while in the heat of desire with a mirror (or live video), the mind tends to filter out unimportant or spurious details so one sees what they want to see instead of everything that is actually there.