An Inexpensive Method for Recording Lectures Without Use of a Video Recorder
Description of the Method
The recording method requires that lectures have been prepared in digital format, in our case, as PowerPoint slides. Figure 1 is a diagram of the components and connections of the system used to present and record the slides. A useful enhancement that we employ is annotation on the slide images using a digital tablet (15“ Hitachi Starboard EM Panel) but this is not required for recording. To record a lecture, the Snapz Pro X program is first launched and runs in the background. The lecture file is opened and PowerPoint is placed in presentation mode displaying the first layer of the first slide. Recording is begun with a keyboard combination that brings Snapz Pro X to the foreground where the full screen area is set for recording and video and audio capture is initiated. At this point, Snapz Pro X disappears and begins to capture screen “snapshots” and the audio signal as fast as the computer will support. Several factors have been evaluated with respect to making optimal recordings.
In our 300-seat classroom, a large screen is needed for all students to have a workable view of the display. To reduce pixelation, we use a 1024 x 768 pixel screen resolution and, since photographs are frequently used in the lectures, the display is set to millions of colors (24-bit) for reasonably faithful reproduction. Thus, each screen image consists of approximately 2.36 mb that the computer must process rapidly enough, in the background to give an acceptable frame rate for the recording. Snapz Pro X must simultaneously capture the audio channel (mono, 16 bit, 22 kHz). In order to achieve a minimally acceptable frame rate (2-4 fps) with these conditions, we found it necessary to use the fastest available Macintosh computer, at the time, a dual 1.0 Ghz processor Power Macintosh G4. It may be assumed that current, faster machines would deliver proportionally higher frame rates but the stream files currently produced have educationally acceptable quality.
When the lecture is complete, other keyboard sequences halt capture and begin assembly of the movie clip. We find it advantageous here to compress the video in MPEG-4 format available with QuickTime© Version 6.x because it affords considerably higher quality streams from the Apple Streaming Server©. Audio is compressed in IMA 4:1 format. Compressing 50 minutes of video and audio on our system requires about 15 minutes and produces a file of about 50 mb. (“Raw” files, compressed only with simple codec’s, approach 200 mb in size) If the computer is available, this processing can be done immediately after class, or, if it will be used in the next period, processing can be delayed (but no further recording can be done until the existing data is processed). The resulting MPEG-4 file is transferred to the streaming server immediately after first-stage compression is complete and we use QuickTime Player Pro© to further process the file as need for streaming [6]. Typically the stream file can be viewed approximately one hour after the class period. The current system does not lend itself to live streaming but that is a function that we do not desire at present.
Table 1 gives the sources of the hardware and software. Aside from the computer itself, system costs are quite modest. We find that considerable educational advantage accrues from live annotation using the LCD screen digital tablet, although it is not necessary for recording and similar benefit can be achieved using a less expensive Wacom© tablet [7]. If the computer used has a built-in microphone input, the USB audio adapter may not be needed. The sound quality of the iMic adapter was quite satisfactory.
Another faculty member, working with a PC, employed the program Camtasia Studio [5] to capture video and audio with results that roughly paralleled those obtained with the PowerMac G4 system but it has not been extensively evaluated. Another trial recording, carried out with a borrowed TabletPC, was promising with especially facile pen annotation but it was necessary to convert the PowerPoint slides into another format before use.