The film was made by Christopher Nupen in 1969 and it was available on
Teldec Video 2292-46293-3 a few years ago.  I am not sure if it is still
available, you can check your local video/music shop or the library.  From
the jacket note:

A film about how and why five of the most gifted young musicians of their
time came together in London in 1969 to rehearse and perform Schubert's
famous Trout Quintet.  The film follows the lives and preparations of the
artists during the week leading up to the concert and it ends with the
complete performance shot live on stage, during the performance in the
new Queen Elizabeth Hall on August 30th.

>From the beginning to end the film is an account of supremely gifted young
musicians enjoying their talents, their special relationship and the music
of Franz Peter Schubert who wrote his Trout Quintet in the Summer of 1819
when he himself was only 22 years old.  It is one of the most successful
Classical Music film ever made.

How often do we have chamber music recital with such a line up now a days?

BTW, there is also a new EMI re-release of another Christopher Nupen
documentary film about Jacqueline Du Pre:  Remembering Jacqueline du Pre
7243 4 77884 3 7.  This one is about her life with footage of rehearsal
sessions and except of her performance of Elgar Cello concerto.

Hope this helps,
Raymond Chan