Complex sentence: Eventually, longer and longer edited-down versions of feature films were issued, increasingly with a magnetic soundtrack and in color, but they were quite expensive and served only a small niche market of very dedicated or affluent film lovers.
Split into simpler sentences: Eventually, longer, edited-down versions of feature films were issued, increasingly with a magnetic soundtrack and in color. But, these were quite expensive and served only a small niche market of very dedicated or affluent film lovers.