Video taken during the launch of AS-203, showing the Saturn IB's S-IVB stage separation. This video was taken by a camera that ejected (seen at the end of the video) and was later recovered from the Atlantic Ocean.
NASA
Taken on 5 July 1966
<a rel="nofollow" class="external free" href="https://archive.org/details/Apollo0616mmOnboardFilm1">https://archive.org/details/Apollo0616mmOnboardFilm1</a> (<a rel="nofollow" class="external text" href="https://ia800504.us.archive.org/1/items/Apollo0616mmOnboardFilm1/apollo6_1_1.mpg">video link</a>)