There are plenty of ways to record two camera feeds. One way is to use a hardware mixer to create a Picture-in-Picture (PIP) view of the two feeds. The downsides to this approach are that quality mixers can be expensive and that they are most appropriate for fixed labs (i.e. they are often too bulky to carry off-site). Another way is to use a commercial software package such as Techsmith’s Morae. The downsides to this approach are that Morae can be relatively costly for some users (such as students) and that Morae requires some post-processing to generate videos from Morae recordings.

The basic idea for our approach is to display both videos on the screen (sized and positioned in whatever way you want) and then record the screen. For our approach, you’ll need to install Windows Media Encoder and software for viewing camera feeds, such as VLC Media Player. You’ll also need two cameras that you can connect to your PC, such as two webcams.

Here are the basic steps:

1. Open up two instances of your software for viewing camera feeds. View one camera feed in each instance. Size and position the camera feeds in whatever way is most appopriate for your needs. For example, you might have the camera feeds positioned side by side or you may have one feed scaled down and positioned in a corner, much like a traditional PIP view (as is shown in the image below). You may also want to consider turning off the window borders (as is shown for the small PIP in the image below).
2. Open Windows Media Encoder and choose the “Capture screen” option. Choose “Region of the screen”. Click the selection button and drag a rectangle around the windows that are displaying your camera feeds. Do not include the title bars on the windows or the Windows start menu/taskbar/notification area. The red rectangle in the image below illustrates the selected region of the screen. Note: Make sure that the values in the “Width x height:” boxes are even numbers; Windows Media Encoder may not work properly if either the width or the height value is an odd number.
3. When you are finished with the Windows Media Encoder setup wizard, click the “Properties” button in the toolbar and choose the “Compression” tab. Click the “Edit” button and change the video codec to “Windows Media Video 9″; this codec works better for capturing camera feeds than the “Windows Media Video 9 Screen” codec that is selected by default. Next, click on the other tab and change the frame rate to 29.97 frames per second.
4. Click the “OK” button and then the “Apply” button. You are now set up. When you click the “Start Encoding” button in the toolbar, Windows Media Recorder will record the area that you specified and save it as a .wmv video. Because of the way that you specified the region of the screen, your video will look as if it was created via a mixer or commercial software.

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There are four different approaches to capturing screen video. The approaches differ in terms of cost, time required to generate a video, and quality. In the following approaches, I use the term target machine to refer to the machine that is generating the screen video that you want to capture.

Approach #1: Record the screen with a video camera

This is the most basic approach – simply point a video camera at the screen of the target machine.

• Pros:
  • This is a very simple approach that can be set up quickly.
• Cons:
  • To capture a screen in this manner, it is often necessary to set up a camera at a slight angle over a participant’s shoulder. If the camera is positioned close to the participant, such as on a tripod behind the participant, it can be particularly obtrusive. Additionally, because the camera is positioned at a slight angle to the screen, the view of the screen appears slightly distorted.
  • Many cameras create video files that require special codecs to watch. If the files are intended to be distributed or shared, it will be necessary to convert the files produced by the camera into a format that can be easily viewed by most people, such as .wmv or .mov. The conversion process can be very time consuming.
  • The quality is typically very low. A standard camera has a resolution of around 640 x 480 pixels, but monitors have resolutions that are potentially many times greater. As a result, video camera recordings of screens appear blurry. Using a HD camera will help reduce blurriness, but quality HD cameras are still somewhat expensive and HD cameras can produce very large files.

Approach #2: Recording software on the target machine

This approach involves installing recording software on the target machine that runs in the background and records the target machine’s screen.

• Pros:
  • There are a variety of free software applications, such as Camstudio, for recording screen video.
  • A number of professional products, such as Camtasia Studio and Morae, include editing features that make it easy to create professional looking videos.
• Cons:
  • Typically recording software is written to run on a major operating system, such as Windows. If you are trying to capture the display of a device that does not run a major operating system, you may not be able to use this approach.
  • The recording software can noticeably slow down a machine. In fact, it is not even possible to use the software on most UMPCs and netbooks.
  • You have to be able to access the target machine to start and stop the recordings. As a result, this software is not practical for remote setups.
  • Some of these software packages require post processing to generate videos. Depending on the output format, post processing may take a time equal to or greater than the length of the video.

Approach #3: Screen sharing

This approach involves recording a shared view of the target machine’s screen. For example, you may connect to the target machine using Windows Remote Desktop and then use recording software on your machine to record the shared view of the target machine.

• Pros:
  • This approach allows for remote setups.
  • Some tools, such UserVue have recording features built in (Note: TechSmith is phasing out UserVue).
• Cons:
  • Some tools for screen sharing, such as Webex, charge by the session or have monthly rates.
  • The quality of screen sharing video may be very low.
  • In many screen sharing setups, audio is handled via a phone connection. Unless you have special equipment for recording phone audio, the quality of the audio capture may be poor. Additionally, the video and audio will probably be out of sync because they are being delivered by two different systems that have different latencies.

Approach #4: Video signal capture

This approach involves using hardware to turn a VGA or DVI signal into a form that can be recorded by a recording application. For example, Epiphan manufacturers a variety of products that have a VGA or DVI input and a USB 2.0 output. The following is one possible setup:

1. Clone the display of the target machine. This is the basic process that you go through to set up a machine like a laptop for a projector.

2.  Connect the VGA cable from the target machine to an Epiphan device and connect the USB output from the Epiphan device to the machine that you’ll use to make the recording.

3.  Use recording software, such as Windows Media Encoder, that recognizes the Epiphan device.

The following are the pros and cons associated with this approach:

• Pros:
  • It is possible to create real time recordings that are very high quality.
  • The recording is done on a machine other than the target machine, so there is no recording software running on the target machine slowing it down.
  • You can record any device that can clone its display. This approach works well for UMPCs, netbooks, and some smartphones.
• Cons:
  • Creating high quality recordings in real time for high resolution target machines requires a good deal of processing power.
  • Hardware devices for converting VGA or DVI inputs for use with a recording machine can be expensive. Devices that support resolutions above 1024×768 and frame rates about 10 fps are particularly expensive.

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The basic design is two panes of glass separated by an airspace. The pane on the participant side is mirrored, and the pane on the observer side is clear glass. There are two design issues involved: light and sound.  Reducing light transmission is the easy part; reducing sound transmission is much more difficult.  If all you wanted to do was control light then you could use a single mirrored pane and be done. The second pane and air gap help reduce sound transmission. You want a STC of 35 as a bare minimum, 40-45 is better. Don’t worry if that doesn’t mean anything to you – future blogs will explain that and provide more details about construction and decorating techniques for reducing both sound transmission and reverberation. In this blog I’ll discuss sound control issues specifically related to the design of the one-way mirror.

Choosing your glass

• Silvering - the glass used in one-way mirrors differs from regular mirrors in that the silver coating is thinner (generally 50% to 75% of mirror silvering), and it lacks the coat of paint typical on mirror glass. Tell your glass supplier that you want glass for an observation room and they will know what you mean. We used Mirropane. Be careful about the cleaning solutions you use on the glass because some can dissolve the coating; check the manufacturer’s instructions.
• Tinting – tinting helps further reduce light transmission. The mirrored glass we bought came pre-tinted. You can also buy untinted glass for the mirrored pane and then apply a tinting film to the unmirrored pane. This has the advantage that you can test out different tints and select one that has a good balance of visibility vs protection from light, but removing and re-applying tints is more expensive and time-consuming.
• Tempering – tempering makes glass stronger and for safety reasons is often recommended for interior windows, but you do NOT want to use tempered glass. The tempering process warps the glass, producing a fun-house effect. The warping catches your eye when you move, continually reminding your participants that they are being observed through a mirror.
• Laminate – you can use either regular glass or laminate. Laminate is safer because it is more likely to stay in one piece if cracked, and it is slightly more soundproof than plain glass.
• Thickness – the specific thickness of the two panes is less important than that the two panes be different thicknesses and/or materials to help reduce sound transmission. Different thickness/material panes have different profiles of the sound frequencies that they transmit, and so two different panes will block slightly different frequencies. You could use 1/4″ and 3/8″ panes, or 1/4″ glass and 1/4″ laminate.
• Size – typical panes come in a maximum size of about 6 x 10 feet. You can connect multiple panes of glass with a thin ribbon of  epoxy or silicone or similar substance and the seams will be barely visible from a distance.
• Weight – glass is about 3.5 times as dense as gypsum (drywall) at the same thickness. Make sure your wall can support the weight of both panes. Larger openings will weaken the wall more.
• IGUs – you do not want to use IGUs (insulated glass units in the US, or double glazed units in Europe) – the maximum air gap of these factory-manufactured double panes is about 1.5″, but you want a 2.5″ – 4″ gap for sound insulation purposes (see below).
• Argon and krypton – these gases are more dense than air. In home and building construction they are commonly used in IGUs to provide additional heat insulation. You don’t want them in your usability lab because they have little value for sound insulation, both because of the sound transmission qualities of the gas and because they require factory-sealed IGUs with too small a gap between panes.
• Triple panes – if a double-paned setup is good, triple-paned would be better, right? Wrong. You want to maximize the airspace between your panes of glass. Assuming your wall thickness limits how far apart you can place your panes, adding a third layer of glass means having two smaller gaps instead of one big gap. The added sound insulation of the third pane is a LOT less than the loss of sound insulation due to cutting your airspace into two sections.

Mounting

• Orientation of the mirror – you’ll want the mirrored side of the mirrored pane to close to and facing the participant. It’s tempting to put the mirrored surface facing into the airspace to protect it from scratches and cleaning fluids. However, glass is slightly reflective, and this may result in a double-image effect where you can see reflections on both the glass and silver sufaces at the same time.
• Gap between panes – the larger the gap, the better sound insulation. At less than 2″ the air acts like a solid and transmits more sound. Every extra inch of gap adds an extra 3dB of noise reduction. Sound studios may use a 6″ to 10″ gap, but this is necessary because they use angled panes, and is achieved by building two separate walls. You’ll want to maximize the gap between the panes, within the contraints of the thickness of your walls. For a usability lab, 2.5″ to 4″ should be sufficient. When discussing this with your glass contractor, they may speak in terms of gap between the glass frames, which isn’t exactly the same as the gap between the panes.
• Angled panes – angling glass prevents reflecting sound back to its source and slightly reduces sound transmission. In a recording studio, controling sound reflection is extremely important, but it’s not an issue for a usability lab. More important is that angling the pane reduces the volume of air between the panes. Sound studios, with a 6″ to 10″ gap, can afford to loose some air volume. If you are installing into a typical office wall, maximizing the volume of air between the panes is more important than an angle. If you have a wide gap and would like to angle one pane, a 1/4″ difference between the top and bottom of the unmirrored pane should be sufficient.
• Wall framing – you can frame out, plaster and paint the opening for the one-way mirror before installation begins. Paint the frame a medium or dark color so that participants don’t see it illuminated with the light from the participant room. Make sure you run all your cables (power, network, audio/video) before you frame the mirror space.
• Sound absorbing material – you can fill the gap between panes with sound-absorbing material like neoprene and foam. We decided this was unecessary. We’ll talk about other room construction methods for reducing sound transmission in future blogs.
• Glass frame – your choice of frame should be guided by the ability to seal all air gaps around the panes and to maximize the gap between panes. We used a snap-in frame that only needs mounting screws on one side so that it can be placed closer to the outer edge of the frame.
• Seal gaps - when installing the frame, caulk around the inside and outside of both frames to make sure there are no air gaps to allow the passage of sound. Close any seams in the framing with caulk or epoxy.
• Dust and prints – be extra careful that there are no fingerprints or construction dust on the pane interiors or frame between the panes, because once that mirror is up you are never going to be able to clean it!

Lighting

One-way mirrors work when the participant side is bright and the observer side is dark, it’s as simple as that. If the moderator wants to turn down the lights because they have a headache that day and the observer wants brighter lights to write on paper you risk turning your one-way mirror into a window and allowing your participants to see into the observervation room. Participant room lighting should be as bright as you can make it moderator and participants a headache. Here are some tips for observation room lighting:

• Dimmable lights – you’ll want to be able to dim the lights during sessions, but your observers may go crazy if they can’t have bright lights between sessions or during setup.
• Blackout curtains – cover any windows with blackout curtains. True blackout curtains are extremely expensive and not necessary for most rooms. Our labs are in a wooded area and don’t get much direct sunlight, so we used drapes we bought at a home linens store, and added light-blocking liners. Mount the drapes several inches higher than the top of the window to minimize vertical light spillage. Velcro can help attach panels together and close gaps between the curtains and the wall. Pick a dark color for the drapes.
• Paint – paint the walls of the observation room and the gap between the panes a medium or dark color. We used gray.
• Doorways – be very careful of doors that can be seen from the participant room that might be opened during a session. Some strategies:
  • Place the door on the same wall as the one-way mirror, if your observation room is wider than the participant room.
  • Keep the hallway outside the door dim by turning off the lights or removing bulbs
  • Most doors can be hung to open on either side; hang the door such that the door itself blocks the hallway from view when opened
  • Build a wall to block sight of the door – in our lab you enter into a short hallway so the door doesn’t have to be closed at all
  • Hang a curtain on the door
• Ceiling lights – avoid lights that can be seen from the participant room. Mount the lights above the one-way mirror so that they are blocked from view by the wall, or use deeply recessed canister lights.
• Monitors – orient monitors in the observation room away from the one-way mirror, and turn down the brightness.
• LEDs and other point sources – avoid lights in the observation room like LED status lights and backlit LCD displays. You can cover lights with static-cling tinting film sold for tinting your own car windows. Watch out for backlit logos on the lid of your laptop.
• Light-colored objects – avoid placing anything light-colored near the one-way mirror because the light spilling in from the participant room will increase its visibility. This includes observers wearing light-colored clothing, white note paper, and white notebook computers.

Additional sources

• How to Build a Small Budget Recording Studio From Scratch (book)
• Sound Studio Construction On a Budget (book)
• Auralex Acoustics: How To Construct A Double Pane Studio Window
• Great Lakes Windows: Sound Control Glazing Options (PDF; has STC ratings for some common panes/IGUs)
• Oldcastle Glass: Sound Control and Laminated Glass (PDF; explains STC; has STC ratings for laminates, by frequency spectrum)

You may also be interested in my previous blog, Does your usability lab need a one-way mirror?

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What is a one-way mirror? It’s glass that has been coated with a thin layer of metal so that it’s reflective, like a mirror. It’s called a one-way mirror because in one direction it’s a mirror, but in the other direction it’s a window. There’s some debate about the proper name – many people call it a two-way mirror because either side can be used as a mirror by changing which room is lit and which room is dark. They’re commonly used in usability labs and focus group rooms, but also in police lineup and interrogation rooms, observation rooms for day care facilities, and to hide a television in your home when not in use. So what is the advantage of a one-way mirror in a usability lab, and do you need them at all?

Advantages of a one-way mirror

• Capture of interactions – you can see all of the emotions on the face of the participant, their body language, and their interactions with both the product and moderator.
• Wide view – you can see the entire room and session context, and are not limited to places that the camera can see. For studies that involve large products or moving around the room, camera views can be very restrictive. For example, we work with Whirlpool, whose lab is a full kitchen with a mirrored wall; watching someone move around the kitchen through a camera is just not the same.
• Makes you focus – there is something compelling about watching actual people that captures your attention; with video, is is easier to get distracted from the session.
• No equipment needed – once the mirror is installed, no equipment is necessary to use it, which means no equipment to break or software to crash during a session.

Advantages of no mirror

• Flexible study room – no need to orient toward the mirror location, or dedicate a wall of the room to a mirror.
• Mirrors make people nervous – some participants notice the mirror and ask about observers behind it, although most quickly forget about it, especially if we have the flexibility to face them away from the mirror. To be fair, you can mitigate this by placing mini-blinds or sheer curtains in front of the mirror, and the cameras in rooms without a mirror make people almost as nervous as the mirror.
• Flexible view – your point of view can be from anywhere you can place a camera, although you can set up similar observation monitors even with a one-way mirror.
• No dedicated observation room – there is no need to dedicate a room as an observation room when you are watching via video streaming. This is great when space is at a premium. Our study rooms do get used as meeting rooms, but our observation rooms are only used for one purpose.
• Lit observation room – you can keep the lights on for taking notes or having a meeting, or sit in a room with windows that aren’t blocked by blackout curtains.
• Sound proofing – it is difficult to design a one-way mirror that is as sound proof as a wall, and even if you do sound may still travel between adjacent rooms. If you have rowdy observers or your observers want to have a working meeting during the sessions, you can increase the separation from the study room so participants cannot hear.

Do you have to have a one-way mirror? No, you don’t have to have it. But if you have the space and run a lot of studies, it’s a great addition to any usability lab. Why do we use one-way mirrors? We prefer that personal view of the participant; it makes the session seem more real and the user’s comments more important because you can clearly see the emotions, body language and hand movements. Also, as a consulting company, we frequently have clients come and observe the sessions, and many of our clients expect it because it’s what they’re used to. But even we don’t always use a one-way mirror. Sometimes we’ll set up in a meeting room in our building and watch via video streaming, or record the session without any observers at all. When we are traveling for field research we frequently make do with whatever we have. But when our clients are traveling with us we’ll arrange for space with a mirror whenever possible because of that feeling of presence you get when watching through the mirror.

I will be discussing this and other topics about usability labs and equipment at the HFES Annual Meeting in October 2009, in a panel titled “Practical Tips for Designing a Usability Evaluation Environment: What Equipment and Software Do You Really Need?”

This article is part of a series of articles about our usability labs. In future articles, we will provide more details about some of the topics touched on in this article, including building a one-way mirror, sound proofing a lab, and streaming video of usability sessions.

Does YOUR lab have a one-way mirror? Do you wish it didn’t? Would you add one if you could? Vote in my poll or drop me a comment below.

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