Chosen answer:The show was recorded on Thanksgiving, 1976. The movie was released April 26, 1978, 17 months later closer to 1.5 years. The movie was not just the straight footage of the one concert, it includes various interviews, studio sessions, etc. filmed at different times. It had to be edited, produced, distribution had to be arranged. Then a release date was picked probably based on some marketing scheme - what other movies were being released around that time, etc. 17 months is not at all an unusual delay for this process.
Chosen answer: The show was recorded on Thanksgiving, 1976. The movie was released April 26, 1978, 17 months later closer to 1.5 years. The movie was not just the straight footage of the one concert, it includes various interviews, studio sessions, etc. filmed at different times. It had to be edited, produced, distribution had to be arranged. Then a release date was picked probably based on some marketing scheme - what other movies were being released around that time, etc. 17 months is not at all an unusual delay for this process.
Myridon