A documentary film is really made in the editing room. You absolutely have to create a general plan or outline in the early stages and carry out production for your characters, stories, and materials, but the real creative decisions that transform these pieces into a complete film are done during editing. In the effort to tell a story, explain a subject, expose characters, and show everything you, as the director, think is important you will likely extend the original running time of the rough cut of the film far beyond what it should be. This is a natural process in documentary post-production and you must then take a keen eye through the film and find ways to cut it down and keep it organized. Here are a few tips for cutting down the overall length of your documentary that work in almost every situation.
Interviews often make up the bone structure of a documentary film as they can tell the story or narrate the B-roll and direct cinema footage. Oftentimes you will find that a certain point is very important, and this can come from the fact that you heard different people say it several times. This does not mean that you have to include it being repeated over and over again just to emphasize the point. Instead you can manipulate the other aesthetics to maximize that specific point, such as changing audio or giving the speaker extra screen time while the other interviews in the sequence all have B-roll over them. Find places where the same thing has been said several times and try to cut it down to just once, or twice in certain situations.
Do Not Include Everything
Everything that is important about your characters, story, and issue cannot go in your film. A film is a different type of medium and you have to make sacrifices about what goes in, which is part of the difference between films and books. What you need to focus on are incidents, topics, stories, and the likes, that help best to focus in on an overarching set of themes, ideas, and personalities you are focusing on. What you can do is look through your film and find how many little avenues your film goes down and see which ones could be cut without actually taking away from the entire film. You may think that these are very crucial, but the film has to be viewed as a totality and the flow of the structure and attention of the audience are even more crucial to its success.
The Small Bits
People do not speak directly, and life does not happen that way either. What this means is that you have to pick through interviews and footage as closely as you can and only take exactly what you need. This does not mean to alter or manipulate what is being said or happening, but you can remove verbal tangents, voice stutters, and in between footage that is not crucial to your actual film. You will be surprised exactly how much of the running time you can take out of a film if you just go through and remove every "umm" that takes place. At the same time you will want to cut down verbal monologues just to their very core bit of information unless they are illustrating something about the character or are important for the style of the film.
Take Out Your Favorite Parts
As was mentioned earlier, a film is viewed in its totality. It is not just the sum of its parts. What this means is that each part of the film must flow together well, and if a part is really great in terms of lines and footage but does not contribute to the film as a whole then it needs to be axed. This can be the most troublesome part of the video editing process, just like it is the hardest thing to do when writing a screenplay. What you need to do is be critical about what your film is in its entirety and how each piece of the film maintains your pacing and overall perspective and feel. If your favorite lines just do not fit in there they are better left in the special features on the DVD.
The absolute best way to take things out of your movie is to show it to several people, have them list what they would take out, and then cross-reference their notes. You will begin to get a general feel about what bores them, what they don’t understand, and what they could live without. This is going to be the absolute best way to know that certain things just have to go.