Part 3 of the surprisingly good 4-part documentary series "The Windsors, A Royal Family" (1994) contains a segment on the 1969 "Royal Family" documentary film.
Apparently, after the success of Lord Mountbatten's TV series, Lord Brabourne (married to Mountbatten's eldest daughter and a film and television producer in his own right) proposed the idea of a film showing the "domestic" side of the Royal Family with an emphasis on "getting to know" the Queen.
Philip Ziegler provides some commentary: initially he believed it was a most successful propaganda film which brilliantly achieved its aim (it was broadcast in the same week as the Investiture of the Prince of Wales).
However, he, like many others, now believes it was a mistake.
Some snippets from the original fim are shown.
" (1969) begins around the 44.20 mark...