Basic Guide to Shooting Video
This paper looks at practical concerns and techniques used in the shooting of video. The intention is to give the beginner tips and tools as well as to highlight some common pitfalls the beginner may encounter.
This document is intended to give the reader a brief introduction into techniques for making videos. As many of the issues relating to exposure, composition, etc. are identical to those encountered with still images, this document will focus on issues which are particular to moving images. Similarly, only the briefest mention will be made of audio concerns, these being covered in documents written for audio recording and also in Audio/Video Production: Recording Lectures, Seminars and Events.
It is important to consider the final form the video will take. If you are shooting something that will appear on a website it is a waste of time and money to use a DigiBeta camera. Conversely, shooting footage on a PD-150 will not produce footage which is generally considered suitable for projection in a cinema (although this is, in fact, exactly what David Lynch did for his film Inland Empire).
This also applies to video formats. Many cameras offer a choice of format, such as DV, DVCAM and HDV. Again, it is useful to consider the end purpose of the video footage. If the only end product is going to be a low-resolution web video clip, then it is a waste of time, money and resources to shoot it in a high-definition format such as HDV. On the other hand, if the footage is one where a very high-resolution image is required or if it is possible that the footage may be used again in the future for an as-yet unspecified purpose, it may be worthwhile to shoot it in as high-resolution format as possible.
After the camcorder itself, your single most important piece of equipment is a good tripod. What makes a good tripod? In a word, weight. A light, small, portable tripod is next to worthless for video work because it is largely incapable of doing the one thing it is intended for: holding the camera steady.
This doesn't mean that you have to lumber yourself with an enormous dead weight in order to shoot reasonable videos. A good, solid tripod for a typical consumer or prosumer camcorder will weigh only a couple of kilograms.
The head of the tripod is equally important and it is here that video tripods and stills camera tripods part company. Unlike a stills camera, a video camera records movement: it will be tilted (changing its up-and-down orientation) and panned (changing its left-and-right orientation) while it is shooting and it is essential that these movements be smooth and deliberate. While a typical stills camera tripod head will allow such movement, its use will not result in smooth movement. For that one needs a video head.
There are innumerable video tripod heads available. It is important to get a head which is rated for the weight of camcorder you are using. The best heads for video work are fluid or semi-fluid heads. These (particularly the true fluid heads) ensure that any camera motion will be smooth.
3. Microphones (on-camera mics vs. separate mics) and headphones
First, if at all possible the use of built-in mics should be avoided. Not only are such microphones generally of a relatively low quality, but there is also the problem of camera noise. Any noise made by the tape or disc transport mechanism, the zoom lens and the aperture (not to mention the camera operator) can and most likely will be picked up by the camera mic.
Second, it is vital that closed-back headphones be worn whenever audio is being recorded that will be used in the final video, as this is the only way to ensure that useful audio is being recorded.
1. Purpose of the video
Before embarking upon a shoot it is vital to consider what the purpose of the shoot is. This is important for several reasons. First of all, it may be that the project doesn't actually need video. Assuming it does, one should determine how video will help the success of the project. Should it be a demonstration or a lecture or perhaps a workshop session? Should it be published on the Internet or used in a PowerPoint or distributed as a DVD? Even if no clear answers to these questions can be found yet, the exercise of considering such issues can only help with decisions that must subsequently be made.
2. Tape and battery requirements
Care should be taken to ensure that sufficient tapes (or discs, or whatever medium is being used) and batteries are taken on a shoot. In the case of tapes, it is particularly important to check the format that the video is being shot in. For example, the same tape which lasts an hour when shooting in DV will only last 40 minutes when shooting in DVCAM.
It is good practice to have sufficient tapes to cover all of the anticipated filming plus at least one extra tape per camera used. Although highly unlikely, it is possible that a tape could jam or be otherwise damaged.
In the case of batteries, always ensure that they are fully charged the night before a shoot. While it is possible (and a very good idea) to get larger-capacity batteries for camera that will cover an entire day's shoot, it is always a good idea to bring along at least one spare battery and the charger - and an extension lead. Remember, too, that you will often be in a situation where the camera can be run off the mains, allowing you to save the battery for when it is really needed.
Tapes (or whatever medium you are using) should always be labelled at the shoot, preferably before they are used. The label should include the name of the shoot, the date, information about how sound is being recorded (camera mic, boom, line in, etc.) and the tape number (it is worthwhile to number the tapes "tape 1 of," "tape 2 of" and so on, filling in the total number of tapes used at the end of the shoot).
Optionally, one can also add the name of the camera operator and any other information that may be useful in post-production - if there's room on the label, of course...
4. The get in and the get out (considerations, health and safety)
Remember when setting up for a shoot that you may want to go back to this location some time in the future, so leave a good impression. Get permission for the location you are using, any furniture or other equipment you need and access to electricity. When you are finished return the location to the state it was in before you arrived (or better).
Typical plug-in RCD
Health and safety concerns should be paramount. All electrical equipment including leads and extension leads should be PAT tested. It is a good idea, particularly when using lighting, to bring along a plug-in RCD (residual current device) and run the extension lead through it; in the case of faulty wiring on a light it may save someone a nasty shock or worse. All cables should be taped down with gaffer tape to eliminate trip hazards. Cameras and other equipment must not block fire exits. And don't leave anything unattended that you don't want stolen.
5. Setting up the camera
Some video cameras allow the user to select the audio sampling rate, generally either 32000 Hz or 48000 Hz. The former will result in a small saving of disk space if the video is transferred to a computer for editing. On some cameras it allows the tape to hold 4 channels of audio instead of 2, but it will also record the audio at a slightly lower quality. However the difference in quality is negligible. On the other hand, the extra disk space consumed by recording at 48000 Hz is also negligible, and while the tape can hold 4 channels, the camera will only record 2 at a time - and 2 channels is enough for most purposes. Probably the best approach is to pick one sampling rate and stick with it, particularly as some older editing programs don't allow you to mix sampling rates.
Many video cameras also allow the user to set up zebra patterning. When this is used, areas of the image in the viewfinder or viewscreen which are exposed above a certain point are filled with a striped pattern. If the camera is set to autoexposure, there is no point in having zebra patterning. However, this can simplify the process of getting a correct exposure when it is being manually set. Like any such guide, it is necessary to experiment and practise with zebra patterning in order to benefit from its employment.
The right of the screen has a zebra pattern, indicating a very bright portion of the image
Image stabilisation is a very useful feature included in many camcorders. It can significantly increase the sharpness of handheld shots but is not necessary if the camera is mounted on a tripod. In addition, all image stabilisation systems are incapable of distinguishing between a jiggled camera and the beginning of a panning movement. As a result, pans may appear jerky as they commence, although newer camcorders have improved software to eliminate much of this jerkiness. On balance, if you are shooting handheld and do not intend to do a lot of panning, image stabilisation is probably a good feature to use - but it is always best to experiment with your equipment beforehand.
1. Holding/steadying the camera with a tripod
An essential part of shooting video is ensuring that the camera is steady and camera movement is smooth. This is easily accomplished with a tripod.
Most modern video tripods include a spirit level in the tripod head. This is a very useful piece of equipment; in fact, if your tripod does not have a spirit level it may be useful to get a small one for your video kit. This is because the eye is easily fooled about what is horizontal, particularly on an uneven surface. In addition, a panning shot that looks level at the start may end up with a slant at the end if the tripod isn't level front and back as well as left and right.
The smoothness of camera motion on a tripod is affected by how you hold the camera and the panning arm. Most importantly, the further from the camera you hold the panning arm, the smoother the movement will be, as any jerkiness will be reduced. It is also often a good idea when using the viewfinder to place some of your weight on the camera by resting your hand on top of it. Your weight will serve to dampen any unwanted motion. In addition, on many cameras you can start and stop the camera and control the zoom with your left hand while panning with your right.
Good one-handed panning technique
Good two-handed panning technique
Bad panning technique
2. Holding/steadying the camera without a tripod
A tripod is not always available or practical for shooting. There may not be enough room to set it up or the shot may need to be lower or higher than the tripod can reach. Perhaps the camera has to be in several different places and the tripod can't be carried around with it. While tripods are always the best way to get a steady image, they are not the only way. With a little practice it is possible to get quite good results without a tripod, either as a hand-held camera or using alternatives to a tripod.
For static shots, the best practice is always to place the camera on something. Almost all camcorders are designed to stand upright on flat surfaces, so any flat, stable surface can be considered as a place to put the camera: tabletops, chairs, low walls, ladders, even the floor. If the surface is not even, place a wedge, a small stone or a tape case under the camera to level it - or shoot the image at an angle. Some camerapersons include a beanbag in their kit for the express purpose of levelling the camera. A coat or jumper can also be very useful for this.
When a level surface of the appropriate height is not available or when you need to pan or tilt the camera it is necessary to hand-hold it. For maximum stability you should follow a few key points. First of all, your legs should be comfortably spread, about a shoulder width apart. You should try and adopt a relaxed posture, not tense, but not floppy either. Use both arms to hold the camera: place your left hand, palm up and fingers facing forward, under the camera to support its weight (if the camera is too small for this, wrap your left hand around your right hand just above the wrist). The right hand is placed through the camera strap (if there is one) to add further stability and to operate the controls. Most importantly, keep your elbows tucked in against your ribs. This is a position which initially may feel unnatural but which adds tremendous stability to your shots. In particular, resting your elbows against your ribs means that your upper arm muscles are not supporting the camera, a situation where they will quickly tire. This is important not only for your comfort, but because as muscles become fatigued they start to introduce small movements.
From left to right: good handheld technique, bad handheld technique. Note that in the good technique the elbows are held against the body.
The most stable support for anything is a tripod, so, if possible, make yourself into one. Two of the tripod's legs will be your own. The third can be provided by a wall, a pillar or a tree which you can lean your back against. You will be able to hold the camera more steadily and once again your muscles will not tire as quickly.
The most important thing to remember about panning is not to do it too quickly. A pan which feels quite leisurely when you shoot it can appear quite rushed when you view it afterwards. There is a technique called a whip pan, where the pan is intentionally executed as quickly as possible in order to provide a place to cut to another scene or simply to disorient the viewer, but it is rarely used.
One should also consider the focal length of the lens when doing a pan. A camera movement which, when the zoom is set to wide angle, results in a slow pan will result in an extremely quick pan when the lens is set to telephoto.
The next most important thing to remember about panning is your body position. The normal tendency for the novice cameraperson is to stand facing the position where the pan begins and then to twist the body as the camera pans until you reach the end of the pan. Panning this way means that, as the pan ends, the body is twisted and as a result very likely to introduce shake into the image.
The correct way to pan is to position the body so it faces in the direction the camera will point at the end of the pan, and then twist it back to the start position of the pan. This way the panning movement is an untwisting of the body, which is then maximally relaxed when the pan concludes.
If the camerperson’s start position is the photo on the left (photo ‘a’) and his end position is the photo on the right (photo ‘b’) then he is using good panning technique: the body untwists as the pan progresses and when the pan has ended the body is in a relaxed, untwisted position.
If, however, the cameraperson’s start position is photo ‘b’ and his end position is photo ‘a’ then he is using bad panning technique: the body twists and tightens as the pan progresses, making it more difficult not to shake the camera or pan it jerkily.
A useful and inexpensive piece of kit which can improve your results significantly is a string tripod. This is simply a bolt which fits into the threaded hole in the base of the camera with a loop of string which is long enough to reach from the camera in its shooting position down to the ground. By placing your foot in the loop you can provide something for your arms to work against, making the camera more stable. In particular, with a little practice you can use this to get very stable and pure panning movements.
Above, a string tripod. Below, string tripod in use.
There are often cases where the camera needs to be held at other than eye level, either because of the thing being shot or not to draw attention to yourself. In particular, one may wish to shoot overhead or close to the ground. When shooting overhead it is good to remember that the arms will not fatigue as quickly if they are fully extended rather than bent at the elbows. This is of course the opposite of the situation when the arms are extended horizontally.
By keeping the arm fully extended (left) the camera can be held steadier for longer. Bending the arm (right) may initially seem more comfortable, but the longer the camera is held like this the harder it is to keep it steady.
When shooting close to the ground it is good practice to hold the camera very loosely by the handle, perhaps only with two fingers, and allow the lower centre of gravity of the camera to keep it horizontal during the shot. You will not be able to work the control during either of these types of shot, but it is worth remembering that video is cheap: when in doubt, shooting extra footage will cost next to nothing but may make or break your shot.
Shooting close to the ground.
3. Viewscreen vs. viewfinder
Several brief points should be made about the relative merits of viewfinders and viewscreens. Viewscreens enable the camera operator to move the camera away from the face: cameras can be held over the head or down at knee level and the operator can still observe the image that is being recorded. Viewfinders, however, still have their advantages. If manual focus is being used the viewfinder provides a more reliable indicator of how sharp the image is. Furthermore there is the sometimes critical point that the viewfinder consumes much less power than a viewscreen. In cases where battery life is a concern the viewfinder may mean the difference between success and failure.
All modern camcorders have autofocus. While this facility greatly simplifies the shooting of video, there are four types of behaviour associated with it which can cause problems.
The first is due to the fact that the autofocus mechanism is designed to focus on whatever is in the centre of the frame. It is quite common when filming lectures or interviews for the subject of the shot not to be centred in the frame. In this situation the autofocus may focus on the wall behind the subject rather than the subject, resulting in an out-of-focus shot. Still cameras provide a means of dealing with this by allowing the user to let the camera focus on the subject and then lock the focus at that point, after which they can compose the shot.
Camcorders don't generally have this facility. Instead they have a means of easily turning the autofocus on and off. Using this is much like the lock focus on a still camera: focus on the subject, then turn off autofocus and compose the shot. The key difference is that the autofocus must be turned on again afterwards.
The second type of behaviour which can cause problems is related to the first. Because the autofocus adjusts itself based on what is in the centre of frame, during a shot which involves camera movement the focus will change. Sometimes this change of focus is welcome, such as when the camera pans from one person to another or from a speaker to a screen. When it is not wanted, autofocus can again be turned off, maintaining the original focus.
The third behaviour which can cause problems occurs when the camera is static on a subject, but the focus keeps changing slightly. Occasionally the autofocus gets into a situation like this where it continually re-adjusts the focus. Again, switching off the autofocus is the only way to deal with this.
Finally the situation occasionally arises where the autofocus fails to respond. The subject is noticeable out of focus and it remains that way. In a case like this the simplest way to re-establish focus is to pan the camera away to an object a different distance from the lens, allow the autofocus to focus on it and then pan back to the subject. If this fails, turning the autofocus off and on again should correct the problem.
Of course, none of these problems occur if the camera is set on manual focus. This is what professional camerapersons do, and while it takes more work and precision on the part of the operator, it is a skill which can be learned quite quickly. The most important thing to remember if you are focusing manually is to zoom into your subject before you focus and zoom out to the frame you want afterwards: it is much easier to focus when zoomed in and much more precise, due to the greatly reduced depth of field of the lens.
There is one caveat to this procedure, however. While almost all modern zoom lenses will keep in focus throughout the full range of the zoom, some will not, Be sure to test your camcorder to ensure that a sharp focus when zoomed in will be maintained when zoomed out.
As with autofocus, autoexposure can result in behaviour that may be problematic, although this is less likely. When changing the framing of the camera the exposure will change, but changes in exposure, unless extreme, are much less noticeable.
A more common problem is one where the exposure needed to correctly see the subject differs from the exposure that autoexposure selects for the image. The most common example of this is when a person stands in front of a window or a screen and as a result appears as a silhouette.
There are two ways of dealing with this. Many camcorders have a switch (sometimes labelled "backlight") which is intended to deal specifically with this issue. Depressing the switch opens the aperture a stop or two above what the autoexposure has set. This will improve exposure of the subject while overexposing the background. However, this may not be the exact increase in aperture needed for a correct exposure. Best results can be attained by turning off autoexposure and adjusting the aperture manually.
On some camcorders the shutter speed selected by the autoexposure results in a strobing effect when recording camera movement or a rapidly moving subject which gives all such movement a jerky look. While this is arguably a bad way to record images, its frequent appearance in videos has resulted in it becoming an accepted style of shooting video. It can be eliminated by selecting a fixed shutter speed on the camcorder.
The quality of the images you record on a camcorder can be significantly improved by remembering a few simple points.
First of all is to be aware of whether or not the camera is level from left to right. This is not to say that it should always be level; rather, one should ensure that the level shots are truly level and the non-level shots are quite clearly non-level. A shot which is only a bit out of level generally looks sloppy. Remember, if your tripod head doesn't have a spirit level built into it, a small one can be purchased at most hardware stores.
This idea of making things look deliberate also extends to camera movement. If the camera is supposed to be still, keep it still; if it is supposed to move, make the movement clear, smooth and deliberate. There was a fashion in several television series a few years ago to have the camera continually drifting around, emphasising that it was being shot with a hand-held camera. This effect can be annoying and is most certainly distracting.
As always there is a counter-example to this practice. It is common when shooting someone speaking to make sure that the camera is not locked in position on the tripod. This is so that the cameraperson can correct the framing when the person speaking moves, as speakers almost always do.
Good composition requires that you think about the camera's position relative to what's being shot - and what's happening around you. If you are videoing an interview with someone sitting in a chair you don't want the camera shooting from a standing level, looking down on the interviewee. If you are recording a lecture you may want to position to get a student's-eye view - but at the same time you don't want to block the view of any students attending the lecture.
Consider, too what else is in the frame. The presence of a legible poster located behind the person you are videoing may tempt the viewer to read it rather than listen to what is being said. Similarly, if some sort of action is being carried out in the background which isn't directly relevant to what is being said, it could prove distracting. A classic error is to shoot a person such that it looks like a tree or a building is growing out of the top of their head.
Three examples of badly-composed shots. Above, people walking down the slope command as much attention as the subject on the right. Below, the subject appears to have a tower growing out of his head
Above, people seem to be walking on the subject's head
Even the choice of focal length will affect the image dramatically. A person on a street shot with a long telephoto can look trapped or lost in crowds of other people, even when the street is fairly empty. Conversely, nothing can destroy the impressiveness of a mountain range or a tall building like a very wide angle lens.
However, the most important guideline for the beginning cameraperson can be summed up in two words: more close-ups. Beginning camerapersons tend to include too much in their compositions, just as beginning scriptwriters include too much in their scenes. By keeping the information in the frame to a minimum we minimise distractions and confusion for the viewer.
The cameraperson should consider where the video will be viewed. Simply put, the smaller the screen, the bigger the objects should appear in frame. It is common practice in the film and video industry to shoot for television differently than for cinema. In particular, television shooting includes far more close-ups and detailed shots of objects. This is even more important in this day of streaming video and mobile devices where the video may be viewed on very small screens.
Try and keep the compositions interesting. A speaker should almost never be shot speaking in the direction of the camera: it is far better to have them facing, however slightly, to one side or the other. Placing a speaker in the centre of frame is both rather boring and unbalanced looking. It is much better to place them off-centre so that there is empty space on the side of the frame they are addressing.
From left to right: a bad frame, a boring frame (not wrong but not very interesting) and a good frame
Finally, if you are shooting video with a still camera or a very small video camera such as a Flip, remember not to rotate the camera 90 degrees to change the framing of the shot: video images can't be rotated the way a photo can. You may, of course, wish to do this as a deliberate effect.
7. Crossing the Line
There is a fundamental concept in the shooting of film which is referred to as “crossing the line.” This concerns the restrictions we must place on how we shoot a scene so that we do not give the viewer contradictory information about the spatial relationships in the scene. If we imagine the scene we are shooting as taking place on a stage, “the line” can be thought of as the front of the stage. As long as we stay on the audience side of the line there will be no confusion about the positions of everything. As soon as we cross the line, however, the viewer will receive information contrary to what has been shown before.
In the case of a scene with two people speaking, the line can be thought of as passing through or just in front of them. Sometimes we have a choice in where we place the line. This is fine, so long as we choose one position and stick to it.
There are always situations where any rule can be broken; so it goes with this rule.
Finally, a counter-example and a bit of trivia. In the 1939 film Stagecoach, the scene where the coach is attacked is famous for being a textbook example of how not to preserve spatial relationships. The line is crossed again and again and the stagecoach is continually changing direction as a result – and it doesn’t matter, because the viewer is so caught up in the action that the discontinuities aren’t really noticed.
8. Shot selection
One of the most common errors novices make is to move the camera too much or too soon. People tend to get restless when shooting video and have a very different impression of the passing of time to the people who eventually view it. In a typical situation the camera operator takes a shot, holds it for what seems like an eternity and them moves to another shot, but when the footage is subsequently viewed it seems that that camera was hardly at rest before it moved on to something else. This is, if anything, even more critical when the footage is to be edited, because the beginning and end of the shot will almost certainly have to be discarded.
A good rule of thumb is to frame the image you want to record and count to 10 before moving on to another shot. Obviously this cannot be a hard and fast rule: if you are capturing a performance, for example, you may suddenly need to shift your attention. But in many cases, such as capturing images to be edited into a sequence later or taking shots of objects, the 10-second rule can be invaluable.
Another area where people move too quickly is at the beginning and end of the shot. Having set the camera to record, it is good practice to wait a few seconds after the red record light is on before getting the person on camera to speak. Similarly the camera shouldn't be turned off the instant the person has stopped speaking.
One should also beware of overlapping speech. If your subject starts talking a fraction of a second after you have told him or her to, it may be difficult to remove your words from the shot without cutting off the subject's.
If you are intending to edit your footage it is essential to shoot cutaways. These are shots which can be used to cover edits in the main footage. For example, you may be shooting a lecture. Before or after the lecture you take some shots of people in the audience listening or simply looking towards the front of the lecture hall. When you edit, if you want to cut out a bit of the lecturer's talk, you can switch the picture to the cutaway at the point where you cut the lecturer's speech and, if properly done, the viewer will not realise that an edit in the speech has occurred.
9. Videoing supporting materials
When videoing an event it may be necessary to shoot all the footage one needs as it is happening. For example, if shooting a lecture it may be necessary to move from the lecturer to a projected image and back throughout a lecture.
However, if the footage is to be edited and time allows, it is far better to shoot supporting materials later and cut them into the finished video. Not only does this mean that there is less chance of missing important shots (in our example, it means that the video could record the lecturer throughout the lecture), but also that the supporting materials can then be shot under better conditions. For example, instead of shooting a large screen, one may shoot the supporting materials on a computer monitor or even shoot paper copies of the materials.
With a little care excellent results can be achieved with a standard video camera and no other equipment. Sheets of paper may be shot on a lectern or even stuck to a wall. Provided the light is adequate and the camera is locked off on a tripod the results will be more than adequate.
If shooting an image from a data projector it is vital that the projector be focused: remember that an out-of focus image can't be re-focused in post-production. This is even more important in this situation where the focus of both the data projector and of the video camera can contribute to a blurred image.
Focusing is less of a problem when shooting a computer monitor but there is a caveat: while one may shoot a modern LCD monitor with no problems, the same is not true of older CRT monitors or televisions. Because of the way such screens work, shooting will frequently result in a horizontal black band across the image which, in worst cases, may slowly descend down the screen.
An example of the black band that appears when videoing a television or CRT monitor.
The correct way to eliminate this problem is to bring in an expensive piece of kit called a scan converter. The best way to eliminate this problem is never to shoot a CRT monitor or TV. However, if there is no alternative, there are two possible ways of dealing with this problem.
The first method is simple and 100% effective, but is only possible with camcorders which permit the user to vary the shutter speed. On such devices one need only set the shutter speed to 1/50 of a second or less (1/60 in the case of an NTSC monitor of the sort found in North America).
The second method is less reliable but should produce good results with a little patience. Where the black band appears on the screen is random, depending on when in the monitor's refresh cycle the camera is switched to record. Each time the camera is turned on, the black band will appear in a different place. Sometimes the band will be off-screen. As a result, if one keeps switching the camera from record to stand-by and back to record, eventually the image in the viewfinder will show no black band and the recording can proceed. The recorded image should be closely watched because the black band may begin to appear at the top of the screen. In this case it will be necessary to switch the camera to stand-by and once again attempt to get the band off screen. This can be fiddly and frustrating, but in the absence of an alternative it will usually work.
10. Loose ends
When you finish recording on a tape, if you do nothing else it is essential to write protect the tape. This is normally performed by sliding a small piece of plastic to uncover a hole in the tape cassette. If you make it a habit to do this as you remove the tape you will go a long way to ensuring that you never accidentally erase footage you have shot.
The write protect tab on a DV tape: The tab should be in the position in the top photo when it goes into the camera prior to the recording, but should immediately be moved to the position in the bottom picture when it is taken out.
For the purposes of editing the footage it is always a good idea to record what is known as "atmos" in the filmmaking world. This is simply the background noise in a room. It could just be the ambient noise or the sound of the air conditioning, but it could also be traffic sounds coming from outside or the sounds of students talking. This sound is useful to ensure that there is uniform background noise in an edited piece of film. It is normal practice to record 30 seconds of atmos in any given location. If you need longer than this in the edit it is a simple matter to re-use the same 30 seconds: this is a long enough time that the listener won't realise that the sound is being repeated.
Don't be afraid to shoot re-takes. You may find that the footage you have taken simply is not good enough. It may be possible to re-shoot the material immediately, but there is no reason not to shoot it days or even months later provided there are no problems with continuity: a lecturer whose hair and clothing change from shot to shot will be, to say the least, distracting.
If every useful point which could be included in this paper were included, it would soon become a book. What we have tried to do here is to give a brief survey of some of the points most useful to a beginner. But the best way for someone to improve their videoing skill is simply to shoot video. Not only will one's general technical ability improve, one will also quickly become aware of other points and ways of working which will contribute greatly to the quality of one's work.