There is a short 3 minute documentary of the North American tour from 1976, then the concert starts.
It has often been rumored that there wasn't a high quality recording of the film in the archives, but this release on 'The McCartney Years' box set shows that there is a high quality print hidden away and hopefully it will be released in it's entirety
Rockshow is a 1980 concert film by Paul McCartney and Wings, filmed during their 1976 North American tour. It features 30 songs from four concerts of the tour: New York, May 25 (four songs); Seattle, Washington, June 10 (five songs); Los Angeles, California, June 22 (15 songs); and Los Angeles, California, June 23 (six songs).
This version was taken from 'The McCartney Years' DVD box set from 2007, but unfortunately only 30 minutes of the concert where included. Paul McCartney has said that he is reluctant to release the whole 30 song concert on DVD.