A/B-roll editing is a term used in linear editing to describe the process of combining two or more sources of raw footage together with transition effects. In the realm of linear editing, it is scientifically impossible to add a true A/B-roll transition effect between two images on the same tape. Why? Because videotape only allows you to play one portion of the footage at a time. To add a dissolve between two shots requires that they be on two separate tapes (source A and source B) played simultaneously in two VCRs. Then and only then can a true A/B-roll transition be performed. (A "false" sort of A/B-roll, called the A/X-roll transition, is possible with one tape; this involves the SEG freezing a single frame of video, then shuttling the tape to a different location and performing the transition from the still to the new moving image. Looks pretty good, but it isn’t a true A/B-roll transition.)
From the equipment standpoint, the A/B-roll editor requires at least two source VCRs (or camcorders in VCR mode), an edit VCR to record the master, an edit control unit to control switching between footage, and a special effects generator to create wipes, fades, dissolves or other desired transition effects.
To perform A/B-roll editing, the editor rolls source A (in play mode) and the edit VCR (in record mode), which records the A-roll onto the master. When a change is called for, the editor cues the transition effect and the B-roll video. This causes the A-roll video to fade, dissolve, wipe or otherwise go away in the midst of some special effect and the B-roll to appear in its place. The point when the two video sources may appear superimposed is called the transition point. When the transition is complete, the A-roll video stops, and the B-roll footage continues to roll until the end of the edit.
Professional film and TV productions often use two cameras to capture their A and B footage sources. For many of us, though, a second camera and another skilled pair of hands to operate it can be hard to come by. The single-camera shooter can just as easily gather footage for A/B-roll editing if he prepares in advance.
<>The Single-camera Solution
Just because most people use a single camcorder to shoot their video productions doesn’t mean they can’t enjoy the nifty effects and variety available from a multi-camera shoot. The trick for the single-camera videographer is to shoot two different tapes of footage with the same camcorder. One tape (the A-roll) typically captures the main subject and action. The other type (the B-roll) typically records peripheral "effects" shots like close-ups, reaction shots, and establishing shots that add drama, variety and context to the primary footage.
STEP 1 Think it Through
Preproduction planning is the first step toward a successful A/B-roll shoot. Think about a traditional wedding shoot. You would probably record some of the pre-ceremony activities, like the bride getting ready, the ushers rolling out the rice paper and the fidgety groom-to-be. Once the music starts, you would then catch the action of the ceremony, including the vows and the ring exchange. From there you would record the couple leaving the church and probably round out the event with some reception footage. Once home, you would edit out the rough spots, hit rewind, and start passing the production out to family members for viewing.
To shoot the above scenario for an A/B-roll edit, you would need to approach the shoot a little differently. First, you would need at least two tapes: one exclusively for A-roll and the other exclusively for B-roll. The A-roll would still capture the high points, but the B-roll would serve to add texture and perspective.
If, for example, in the middle of the ceremony, you wanted to dissolve to a shot of the bride’s parents, it would be a special effect indeed to keep the camera on the altar and also record the parents. A/B-roll shooting gives you the ability to "cheat" a shot like this. In this example, you would shoot the parents at some point before or after the ceremony, with a separate tape in the camcorder (the B-roll). This also illustrates how single-camera A/B-roll shooting is very deliberate. Every shot is planned and lined up.
Step 2 Write it Out
For single camera A/B-roll shooting, a shooting plan is important to make sure you acquire all of the footage you might need. The plan can be anything from a simple handwritten form to a detailed storyboard. To help expand your compositional horizons, borrow a trick from the book of great Hollywood directors and try to pre-visualize the entire shoot beforehand. Try to establish a mental picture of what the finished production will look like before you start. Now write it down. For many videographers, this will be in stark contrast to their typical "get what you can, when you can" shooting style, but it will pay substantial dividends in the quality of the finished production. Even though every videographer will "see" an event differently, certain shots are essential to ensure proper coverage of the proceedings and a script will make sure you don’t miss any in the confusion.
As you consider an event, try to break it into logical scenes. This will help determine what you must shoot for A-roll and what you can fit in for B-roll. In the case of a wedding, the ceremony would be the A-roll. A good way to begin many videos, for example, is with an "establishing shot," which is usually an extreme long shot that sets the scene for the viewer. This first shot quickly orients the viewer, gives context to the scene and allows a smooth "entrance" into the tape. If you determine that you would like to dissolve from your establishing shot of the church to the bride’s entrance, the church shot must be on the B-roll tape. Include this in the script, along with all the critical elements of the event. Now go back and brainstorm other B-roll shots that relate to the main action and can transition well in between. Remember, any two shots to include transition effects must be shot on different tapes. This makes planning ahead essential. For single camera A/B shooting, try to choose transition scenes that are easy to get and that you can shoot before or after the main action at your leisure.
Step 3 Shoot the A-roll
Great B-roll won’t do you much good if you miss critical parts of the A-roll action. The important A-roll scenes must take priority. When taping a wedding, for example, pausing the tape during the ceremony would be disastrous as you would create breaks in the audio track. B-roll can be used to cover camera moves, but will never replace footage that is critical to the production.
Breaking down a production or event into its component parts allows the single-camera shooter the opportunity to decide which parts of the event are most important. Your primary footage makes up your A-roll, and you don’t want to leave any out. Practice good framing, good lighting, good angles and other solid composition rules with your A-roll. Save the experimentation for the B-roll, where it’s easier to cover up a miscue.
Step 4 Get Enough B-roll
One of the keys to remember when planning your shoot is that each segment of tape you plan to use as part of an A/B-roll transition must be long enough for editing. Each shot must last at least 10 seconds to cover usable footage, plus the preroll requirements of the editing system.
Preroll is the term used to describe the time it takes for the videotape in the source machine to stabilize, which is commonly about five seconds. Add another five or more seconds of video footage for the actual transition, and you can see how the 10-second rule-of-thumb came about. It is a good practice to shoot at least 30 seconds of every B-roll shot, just to be certain that you have enough usable video to perform a smooth, visually pleasing transition.
Often, you must look beyond the main action of a scene to find the details that make for interesting A/B-roll transitions. In the case of a wedding, for example, you might show a wide shot of the church as ushers are seating guests, music is playing and candles are lit. A closeup of a candle as it takes flame would make an interesting dissolve, and you can easily shoot it before anything else happens. Shots like these allow for creative A/B-roll editing without causing concerns about continuity. It would be pretty tough for a viewer to discern if the candle shown in the extreme wide shot is the same candle in the extreme closeup.
Step 5 Repeat as Necessary
When planning your video, you may want to include transitions from one angle of a shot to another angle of the same action. This is a simple feat with multiple cameras recording the same scene from different perspectives. Although it may seem impossible with a single camera, in some instances there is a solution. A tricky way to copy the look of a multiple-camera shoot is to repeat the action and shoot it twice (or more) from different angles.
Used extensively in the production of feature films, repeat action shooting allows for many options in A/B-roll editing. In situations where multiple takes are possible, the single-camcorder videographer can use this method. Even for a wedding video, it is possible to ask the bride and groom to re-enact key moments of the ceremony. Note that still photographers often do exactly this. This way you can get a closeup, say, of the ring going on the bride’s finger to edit into the master shot as B-roll. Other projects lend themselves to repeatable action as well. Step-by-step instructional tapes, product demonstrations and music videos are all perfect candidates for repeat action coverage.
First record the entire scene as a wide shot. Then, repeat the scene several times, recording from a variety of angles to provide close-ups or more interesting details of the major characters and actions. You can use repeat action for the entire scene, or just with a section of the tape that’s prime for a transition between angles.
Two tips help this "cheat" become more convincing: the talent’s ability to closely mimic earlier action and the use of overlapping. When shooting the same action in multiple takes, it is important for any on-camera subject to repeat the physical action as closely as possible to the previous takes. If the guitarist in your music video jumps into the air after a particularly challenging solo in the first take, the guitarist needs to repeat that jump in each successive take.
Overlapping is the technique of beginning each new shot by repeating the action or dialogue that ended the previous shot. By providing a visual and audio reference of what happened immediately before the new section, final editing and lining up of transitions becomes much easier and more professional looking.
Don’t overlook the basics of good shooting technique in your quest to get A/B-roll footage. When you are planning your production, in addition to planning the transitions, try to visualize the "look" of the transitions as well. We’ve all witnessed an awkward cut in a program where, for whatever reason, things just don’t go together right. The same can happen with dissolves, wipes and fades.
Mismatched lighting can make for the most unpleasant transitions. A low light long shot of a wedding ceremony that dissolves into an overbright outdoor shot will appear jarring. Try to maintain a similar light level between A/B-roll shots, unless, of course, you purposely want a visual shock.
Camera movement can also throw off a transition. If the A-roll footage features a slow pan from left to right, you want the B-roll footage to feature a similar movement in direction and speed. While zoom-in/zoom-out combinations can work together, too much movement can confuse a viewer.
Finally, don’t discount sound in your productions. The addition of sound segues, musical transitions and voice-overs all help to elevate the professional feel and polish of an A/B-roll edited production, whether you are shooting with one camcorder or five. Put at least as much time into developing the sound portion of your tape as you do the video.
Shooting for A/B-roll editing with a single camcorder takes a little more planning and a little more effort than using just your primary footage. However, if you want to improve the quality of your videos, the extra effort is worth it.