Complex sentence: However, the footage from these concerts was deemed unsatisfactory, partly due to the film being grainy and unusable, but also because some of the sound had been recorded on different channels and was virtually inaudible.
Split into simpler sentences: However, the footage from these concerts was deemed unsatisfactory: one of the reasons for this was that the film was grainy and unusable. Secondly, some of the sound had been recorded on different channels and was virtually inaudible.