Exchanging digital video of laryngeal examinations

Exchanging Digital Video of Laryngeal Examinations John M. Crump and Thomas Deutsch Lincoln Park, New Jersey

Summary: Laryngeal examinations, especially stroboscopic examinations, are increasingly recorded using digital video formats on computer media, rather than using analog formats on videotape. It would be useful to share these examinations with other medical professionals in formats that would facilitate reliable and high-quality playback on a personal computer by the recipients. Unfortunately, a personal computer is not well designed for reliable presentation of artifact-free video. It is particularly important that laryngeal video play without artifacts of motion or color because these are often the characteristics of greatest clinical interest. With proper tools and procedures, and with reasonable compromises in image resolution and the duration of the examination, digital video of laryngeal examinations can be reliably exchanged. However, the tools, procedures, and formats for recording, converting to another digital format (“transcoding”), communicating, copying, and playing digital video with a personal computer are not familiar to most medical professionals. Some understanding of digital video and the tools available is required of those wanting to exchange digital video. Best results are achieved by recording to a digital format best suited for recording (such as MJPEG or DV), judiciously selecting a segment of the recording for sharing, and converting to a format suited to distribution (such as MPEG1 or MPEG2) using a medium suited to the situation (such as e-mail attachment, CD-ROM, a “clip” within a Microsoft PowerPoint presentation, or DVD-Video). If digital video is sent to a colleague, some guidance on playing files and using a PC media player is helpful. Key Words: Digital video—Laryngeal stroboscopy—Stroboscopy— Laryngeal video stroboscopy—Sharing video.

INTRODUCTION Prior to the late 1990s, video signals were generally recorded to videotape using an analog videocassette recorder (VCR). Although there are many recording formats, VHS or SVHS were usually used because of their low cost and widespread availability. However, just as analog audio media have slowly been replaced by digital audio (LP records, for instance, have been supplanted by music CDs), analog video is being replaced by digital video. Digital video is commonly delivered on DVDs and as short clips over the Internet. Camcorders are also evolving from

Accepted for publication April 3, 2003. This work was presented at The Voice Foundation’s 31st Annual Symposium: Care of the Professional Voice, June 5–9, 2002, Philadelphia, PA. From Kay Elemetrics Corporation, Lincoln Park, New Jersey. Address correspondence and reprint requests to John M. Crump, Kay Elemetrics Corporation, 2 Bridgewater Lane, Lincoln Park, NJ 07035. E-mail: [email protected] Journal of Voice, Vol. 18, No. 1, pp. 13–23 0892-1997/$30.00 쑕 2004 The Voice Foundation doi:10.1016/S0892-1997(03)00087-0

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JOHN M. CRUMP AND THOMAS DEUTSCH process. As medical records migrate toward more easily shared electronic formats, it would be useful for medical professionals also to know how to share large laryngeal video examinations.

THE CHALLENGE

FIGURE 1. Digital video, depending on the application, employs a wide range of media and formats. Computer video is a relatively small application area for digital video.

analog formats such as Hi8, VHS, and SVHS to a digital format named DV. This evolution to digital format is also being realized in the recording of medical examinations. The desire to meld laryngeal examination video and physiologic information, examination reports, image printing, patient database, archiving, and computer management of examinations makes personal computers (PCs) the preferred recording platform. The Kay Digital Stroboscope (Kay Elemetrics, Lincoln Park, NJ) system is one of the commonly used systems for this purpose. It is based on a PC and incorporates special software and hardware designed for the recording of laryngeal examinations. Although its most critical use is the recording and playback of an examination within a particular practice, it would also be useful for medical professionals to know how to record, transcode (that is, convert to another digital format), and exchange digital video so that laryngeal examinations can be reliably viewed by other medical professionals using unmodified PCs and without the motion or other artifacts commonly associated with video display on a PC. Given the relative ease of copying and of electronically exchanging digital video, this is achievable if the user has some understanding of the conversion Journal of Voice, Vol. 18, No. 1, 2004

In order to successfully share a video of a laryngeal examination in digital format, the appropriate method for recording, converting (“transcoding”), and sharing it must be chosen. The format and sharing methods should allow the recipient of the video to view it artifact-free on a PC with sufficient resolution to show the laryngeal behavior and anatomy of interest. Digital video has numerous recording methods, recording formats, and delivery media (see Figure 1). Delivery of digital video is subject to various methods and tools for recording video, to the inherent limitations of the PC for handling video, to the numerous semicompatible media players, the difficulty in selecting the appropriate video compression/decompression (CODEC) algorithms, and the many video delivery formats. The variety and complexity of digital video procession is at least partly the result of the wide range of applications to which the material is put. Each has its optimal formats, CODECs, image resolutions, and delivery media. On top of this, the technology for digital videos and the capabilities of the PC to cope with digital video are rapidly changing. Some understanding of the underlying science of video recording is helpful in using digital video most effectively.

VIDEO SIGNAL What is video? In the first half of the 20th century, the most common medium for recording and presenting moving images was the reel of film, from which a series of images could be presented quickly enough so that the viewer perceives smooth motion. Video is an electronic version of film. It consists of individual horizontal lines that are sequentially drawn on the screen in response to “horizontal synchronization signals.” The horizontal lines fill the screen with a

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FIGURE 2. Analog video uses an interlaced display, whereas computers use a progressive display. Most video is recorded from cameras, which generate an interlaced output.

field of information. The fields are drawn sequentially in response to “vertical synchronization signals.” Two fields are interlaced to form a single video frame (see Figure 2). The frames are generated quickly enough that the viewer perceives a relatively accurate representation of motion. When the methods of analog video transmission and display were developed in the early years of television, a number of standards were agreed on. “NTSC” is the standard video format used in North American, Japan, and many other countries. Other formats include PAL (most of Europe) and SECAM. Table 1 provides some information about these video standards. Within the respective countries, the cameras, transmission, display, and recording devices all conform to the appropriate standards.1

consumer applications. Its combination of low cost, reasonable recording duration, and small size led to its common use in medical applications despite its low resolution of 240 lines (horizontal axis). The SVHS standard offered an enhancement to 400 lines. It gained limited acceptance in the consumer market, but it found more widespread use in laryngeal video recording, thanks to its higher resolution.

Analog recording media At its start, television was live. Analog videotape, which was developed later, records each field of the video signal as a helical scan on the tape. In the pause–play mode, a single field is replayed. In play mode, a succession of fields is played. In the 1970s, the VHS videotape standard became ubiquitous for

TABLE 1. Analog Video Formats

DIGITAL VIDEO A video camera, even a “digital camera,” includes an analog device (eg, charge coupled device (CCD) integrated circuit) for detecting the image. In digital

Lines: Interlace: Field Rate: Frame Rate:

NTSC

PAL

SECAM

525 Yes, 2:1 59.94 Hz 29.97 Hz

625 Yes, 2:1 50 Hz 25 Hz

625 Yes, 2:1 50 Hz 25 Hz

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FIGURE 3. Video digitizing in a PC is a subset of general video digitizing.

video, the analog signal is digitized using an analogto-digital (A/D) converter. To represent motion accurately, all of the video information (that is, every field) must be captured and stored in real time. Further, due to the large stream of digitized data (⬎20 MB/second), the video images are usually compressed during recording (see Figure 3). The quality of the processes and components used in the digitizing and compressing of video varies widely.2

COMPRESSION A standard NTSC video frame, when digitized, is commonly represented with 640 (horizontal) × 480 (vertical) dots or “pixels,” each of which is made up of a combination of three colors (red, green, blue). One uncompressed video frame, therefore, requires 640 × 480 × 3 ≈ 921 thousand bytes (KB) to store. At a rate of 30 frames per second, approximately 1.6 billion bytes (GB) are needed to save one minute of uncompressed video. Most PCs cannot store the stream of uncompressed video data quickly enough, and even if they could, the hard disk on which the information is being stored would fill up quickly. Compression reduces the amount of storage space that is needed. Almost all compression algorithms take advantage of the limitations or peculiar Journal of Voice, Vol. 18, No. 1, 2004

properties of human perception to reduce the quantity of data. For example, the human eye does not perceive changes in color as much as changes in brightness. Many algorithms, therefore, reduce the amount of color in each frame without noticeable degradation. When compression is performed on each frame individually, it is called “intraframe,” and when it is accomplished using several frames at once, it is referred to as “interframe” compression. Intraframe compression schemes look for commonalities within each frame. For instance, in an image of a blue sky, there are many neighboring pixels that are identical and do not need to be stored individually. They can be saved as a group to save space. Interframe compression takes advantage of the fact that successive frames are typically very similar. For example, often a small part of the image shows any motion. With an interframe imaging compression algorithm, the portion of the image that is not changing can be represented without unnecessary replication, essentially by saving the original frame and then saving only information about changes to that original. This requires much less storage space, but at the expense of more complex processing. When used during recording, the compression process must be fast enough to keep up with the incoming data stream. This is difficult for interframe algorithms to achieve while maintaining

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FIGURE 4. Uncompressed video consumes memory much faster than do compressed formats.

high image quality. Therefore, most digital video recording formats do not use interframe compression and use the intraframe method at minimal compression (Figure 4).

CODECS CODECs perform compression and decompression of the video image. A CODEC is a specific, sometimes-proprietary, algorithm. CODECs take on many forms and are specified in the digitized video file. When the file is played, the computer media player program identifies the CODEC and then loads the appropriate software in order to play the file. The CODEC may be in the form of software or, if high-speed processing is needed, in the form of custom-designed hardware. Three main criteria govern the choice of a CODEC: file size, image quality, and compression/ decompression speed. In general, each of these criteria will have to be traded off against each of the others. MPEG-1, for example, will yield digital video files that take up very little storage space, but they will be lower in quality. MPEG-2 offers high image quality, but at the price of larger file size. The compression methods and usual applications of common CODECs, MJPEG, AVI, MPEG, Cinepak, Video1, and DV, are listed in Table 2.

MEDIA PLAYERS A media player is a program that loads, displays, and controls the playback of digitized media, both audio and video. The player uses different CODECs, available in the computer, for decoding the video files. Examples of media players include Active Movie Player, Media Player, Windows Media Player (Microsoft Inc., Redman, WA), Real Player (RealNetworks, Seattle, WA), QuickTime (Apple Computer Inc., Cupertino, CA), and Power DVD (Cyberlink, Taipei Hsien, Taiwan, R.O.C.). Not all media players play all types of files. Media Player, for example, might not have the correct CODEC to play an MPEG2 file, but it can play MPEG1 and AVI files. Computers are often set to recognize the extension of the file name and, on that basis, to call the proper media player into action. If the file extension is not automatically recognized, it may be possible to download the correct CODEC from TABLE 2. Common CODECs Format

Compression

Application

MJPEG MPEG1 Cinepak MPEG2 AVI DV

Intraframe Intraframe and Interframe Intraframe Intraframe and Interframe Intraframe Intraframe

General CD-ROM, Web CD-ROM, Web DVD, digital satellite General computer Consumer video

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JOHN M. CRUMP AND THOMAS DEUTSCH TABLE 3. Characteristics of Recording and Distribution Formats

Compression: File Size: Encoding: Decoding: Ability to Edit File: Transcodable:

Recording

Distribution

Minimal Large Fast (in real-time) Fast (in real-time) Easy Very desirable

Very compressed Small Not required Fast (in real-time) Difficult Not required

the Internet. Whenever digital video is sent to someone else’s computer, the sender should select a video format and CODEC that the recipient’s computer is likely to support. Recording and distribution formats Although there is much overlap, digital formats can be conveniently divided into two types, recording formats and distribution formats. Video over the Internet, for example, is usually transmitted with a great deal of compression, with limited quality, and with a low frame rate in order to reduce the amount of information that must be handled by the relatively low data capacity (“limited bandwidth”) of most personal computers connected to the Internet. These highly compressed formats are termed distribution formats; they are not well suited to real-time recording. On the other hand, a digital camcorder, for live-recording use, will probably use a recording digital format (eg, DV). These formats are well suited to real-time recording, in that they achieve the best video quality that the hardware can support, are computationally quick to compress in a single pass, and the formats facilitate easy access to each field for editing. The very large data files that recording formats produce make them a poor choice for distributing video (Table 3). Because recording and distribution formats are at cross purposes, most video for distribution is first produced in a format best suited to recording (that is, in a recording format) so as to optimize recording quality within the limitations of the available recording equipment and budget. The recordings are then transcoded into a more suitable format (a distribution format) chosen on the basis of the distribution method that is planned, the needs of the recipient, Journal of Voice, Vol. 18, No. 1, 2004

and the equipment on which the video is likely to be displayed.

PC CONSIDERATIONS Personal computers were originally developed to process and display text and numerical calculations. Still-image and video capabilities are a more recent evolution, and the recording and display of full-size, full-frame-rate video remains difficult for the PC to process without display artifacts. The PC is severely challenged by the demand for system bandwidth, intensive video processing, fast display memory, and fast transfer from online storage media. Because most networks, or the Internet, cannot carry video data fast enough to meet the needs of uninterrupted real-time viewing, an entire video file must be gathered and stored (ie, buffered) by the PC before playback. PCs with DVD-ROM drives usually are capable of playing DVD-Video movies.

RECORDING LARYNGEAL EXAMINATIONS Recording and playback of laryngeal examinations is especially challenging for a PC because it is critical to avoid video artifacts, which could be confused for episodes of abnormal laryngeal behavior. Color accuracy and image resolution must also be adequate for the assessment of tissue properties.

VIDEO FORMATS Salient characteristics of the most common video formats are summarized in Table 4. Some additional details are considered below. VIDEO FORMAT—DV A camcorder combines a video camera and a video recorder. In the past, camcorders usually used analog formats and media, but most new models employ the digital recording format called DV, which has become a convenient standard method. A tape-based format, DV involves minimal (5:1) compression using an intraframe technique. The audio portion, which is in stereo, is not compressed.

Easy Play, frame jog forward and reverse Easy Play, frame jog forward and reverse Difficult Play, frame jog forward Difficult Play, frame jog forward

Great Adequate No

DVD Player Compatibility Video Quality Accommodates EGG and Physiological Data Editability Playback attributes

Resolution Data Rate: (MB/sec.) Sampling Rate Flexibility PC compatibility

Compression Method Format Type

Difficult Play, frame jog forward

Easy Play, field or frame jog forward and reverse

None Varies No

Variable Variable, high Yes Good

720 × 480 3.66 None Fair—special software needed None Excellent No 720 × 480 1–2.5 Yes Needs Kay system or transcoding None—needs conversion Exceptional Yes

Intraframe Distribution

Computer file

DV tape or computer file Intraframe Recording Computer file or DVD ⫹ RW Intraframe Recording

Super Video CD or DVD or computer computer file file Interframe Interframe Distribution Distribution (Playback) (Playback) 480 × 480 720 × 480 0.166–0.332 0.5–1.16 Limited Limited Poor—decoder Poor—decoder needed needed Good Excellent Good Excellent No No Video CD or computer file Interframe Distribution (Playback) 320 × 240 0.166 Yes Good Media

Kay proprietary (MJPEG) MPEG2 for DVD MPEG2 for CD MPEG1

TABLE 4. Digital Video Formats.

DV

AVI

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The resulting video file takes up a significant amount of space, 3.5 megabytes (MB) per second of recorded material. New camcorders usually include a digital DV port (also named iLink, Firewire, or IEEE-1394) that allows DV signals to be transferred in and out of an appropriately configured computer. Because DV is tape-based and only minimally compressed, it is poorly suited to video distribution. Most users transfer video from their camcorder, edit the video on their PC, and then transfer the edited video back to tape. If the video information is to be kept in the computer, it is usually converted to more compact formats for storage and later distribution. Although a common standard, tools for recording, playing, and editing DV are not included with most PCs. VIDEO FORMAT—DVD—VIDEO DVD-Video is the format used for DVD movies, and it is designed for distribution of high-quality video.3 The target hardware playback device is a stand-alone DVD player. DVD-Video uses a combination of intraframe and interframe methods to produce a highly compressed (eg, 50:1) video file. (DVD-Video is a specific version of MPEG2, whereas the associated audio material is compressed using the MP3 format.) Material intended for DVDVideo is typically recorded in some other recording format and then converted. The final product is thus the result of a multistage process of recording, editing, transcoding, authoring, mastering, and replicating. There is a wide range of tools for accomplishing these processes; they vary in cost, quality, versatility, and degree of automation. If the DVDVideo is to be reproduced in large quantities, commercial “printing” processes are available. Otherwise, the recording can be replicated on a peripheral drive (eg, DVD-R, DVD ⫹ R, DVD ⫹ RW) installed on a PC. To play a DVD, a computer must have a DVDROM drive and appropriate software. Systems that have only a standard multimedia player or CD-ROM usually cannot accommodate the DVD-Video format. This limits its suitability as a distribution medium. Although a great distribution format for those recipients who have either a DVD-Video player or Journal of Voice, Vol. 18, No. 1, 2004

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DVD-ROM in a computer, DVD-Video is not well suited as a recording format and it is not playable to a typical PC without a DVD-ROM drive. Some realtime DVD recorders have recently been introduced and evaluated by the authors. These are promising, but they have significant limitations for laryngeal recording.

VIDEO FORMAT—AVI Whereas DVD-Video and DV are specifically defined digital video formats with specified data rate and resolution characteristics, Audio-Video Interleaved (AVI) is a broad class of intraframe compression standards with flexibility about resolution and codecs. (DV, in fact, is one type of AVI.) Various types of AVI CODECs have been available in PCs for some time, making AVIs highly portable. Kay’s Digital Stroboscope systems have included the ability to convert to AVI using a Microsoft CODEC. A significant limitation of the generic AVI format is that compression rates are not very high, so that considerable media space is needed to store even small images. Although still useful—for instance, for videokymographic displays, to be discussed later—AVI creates files that are prohibitively large for sharing digital images unless the duration is very short (eg, less than 5 seconds).

VIDEO FORMAT—MPEG1 Very similar to DVD-Video, MPEG1 uses a computationally intensive interframe compression algorithm to produce smaller, highly compressed files with less image resolution. It is not suited to recording, but it is commonly used as a distribution format. Most modern PCs have CODECs for playing MPEG1 (and, if not, one can be obtained free of charge from the Microsoft website: http://www. microsoft.com.).

TRANSCODING Transcoding is the process of converting a digital video from one format to another. Because video is usually recorded using a format best suited for Journal of Voice, Vol. 18, No. 1, 2004

recording (eg, DV or Motion JPEG) and then delivered in a format best suited for distribution (eg, MPEG1 or DVD-Video), the video and audio data needs to be reformatted (ie, transcoded) into the new format.4 There are numerous settings (eg, constant bit rate, variable bit rate, audio compression, etc.) and selections in the transcoding process. The transcoding process, depending on the source and output file types, can vary in processing speed. Usually, it is slower than real time. Therefore, it may take, for example, 30 seconds to transcode a 10second video segment. RECORDING LARYNGEAL VIDEO STROBOSCOPY SYSTEMS Digital video recording systems are different from those systems used to edit and make distribution video. This is especially true for laryngeal video stroboscopy recording because of its unique demands. Full-resolution, full-motion artifact-free recording of laryngeal video stroboscopy requires a dedicated system with features designed for this task. The Kay Digital Stroboscope system is the most widely used instrumentation for digitizing the video images of laryngeal stroboscopic examinations. The latest version of the system is based on a Windows 2000–based system tested for medical environments. The computer has custom software, custom hard drives, and plug-in cards for digitizing the video, acquiring the associated audio and electroglottograph signals, and controlling the video camera. The system is on a cart designed for operation in a standing position, the camera is controlled by the software in order to achieve optimal and reliable color settings, and a foot pedal is used to control basic actions such as starting and stopping recording. Unlike video-editing workstations, the software automates saving, archiving, and reporting functions. It also insulates the examiner from most of the complexities of handling video in a computer; for example, it automatically defragments the drives. These requirements for a laryngeal video recording system are also difficult to reconcile with the desirable characteristics of a system designed for editing and making distribution video. The native record/playback format of the Kay Digital Stroboscope system is designed for artifact-free recording

EXCHANGING DIGITAL VIDEO using a dedicated hardware compression board. As a result, the recorded files, in their native format, cannot be played on any computer system. Playback on more generic computers (or on a DVD player) requires a special viewing program or that the video and audio files be transcoded into a distribution format. Utility tools are included in the Kay system to do this transcoding. The ability to distribute decent-quality video comes at a cost: In the transcoding process, some features, such as concurrent Electroglottograph (EGG) display, field jogging, frequency, and intensity information, can be lost and the quality of the image is reduced. AVI transcoding is built into the Kay application program, and other tools are available in the system to convert to other digital video formats.

VIDEOKYMOGRAPHY Videokymography, as described by Schutte, Sˇvec, and Sˇram5,6, is a uniquely revealing video technology for examining vocal fold behavior. It uses a special camera to record approximately 8,000 line scans per second, and formats these lines scans into continuous video fields. (A nontechnical discussion of the videokymographic method is provided in Baken and Orlikoff.7) Each field shows a short history of laryngeal behavior: 1/60 s in NTSC or 1/50 s in PAL. In order to view continuous laryngeal behavior, it is necessary to see both even and odd video fields. Videotape players show only the odd fields and do not display contiguous segments. Kay’s Digital Stroboscope system uses a proprietary recording file format that records and displays each video field. Its native format is optimal for videokymographic display because of its ability to jog to each field. The recommendations in the next section suggest standard media file formats (MPEG1 and MPEG2) for distribution of most laryngeal video. These formats, however, use only the odd fields in the transcoding process. Thus, like videotape players, they would not show continuous information for videokymography. Microsoft has developed special features in their media encoders, which allow conversion of both fields of video to a multimedia format. To date, these tools have not been completely

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evaluated by the authors. Until they are fully researched, we recommend that, despite its limitations, the AVI format is used for videokymography.

RECOMMENDATIONS Introduction The Kay Digital Stroboscope is used as the basis for the following recommendations because of its wide availability. Once recorded, the digital video can be transcoded to the format most appropriate for how the video is to be shared. Although the AVI format can still be used, the MPEG1 and MPEG2 formats are better suited to the exchange of video with generic PCs (with the exception, as noted earlier, of videokymographic files). Because these formats are compressed and relatively common, there is a high probability that the recipients of the file will be able to play it on their PC. MPEG1 playback is a standard feature of the later versions of Windows Media Player, which is available at no cost from Microsoft. The choices of media type and conversion process are dependent on the specific application, as described below. Recording and transcoding recommendations All of the scenarios described below require that the laryngeal examination(s) be recorded and transcoded. To accomplish this, one needs to: 1. Record the video examination with the Kay Digital Stroboscopy system. 2. Use the utility software supplied to transcode a segment to MPEG1. Select 320 × 240 resolution, which is a 4:1 reduction of resolution from the original. It is necessitated by the fact that not all computers can play back the higher resolution without display artifacts. The duration of the transcoded section will vary depending on the application. 3. Assign the resulting file an appropriate name and store it in a subdirectory.

Sharing digital video for e-mail It is common for health care professionals to want to share video examinations with colleagues at other Journal of Voice, Vol. 18, No. 1, 2004

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locations. This can be accomplished, with due regard for the limitations of resolution and segment duration mentioned above, by sending the examination file with an e-mail as an attached “standard” digital media file. Be very mindful of the need to protect patient privacy and confidentiality. To share an examination via e-mail: 1. Follow steps 1–3 above. Transcode no more than approximately 10 seconds to MPEG1. The restriction is imposed because many email systems may automatically reject larger e-mail attachments. 2. Use your e-mail program to attach the multimedia file created in step 1 to the e-mail message. 3. In the body of the e-mail message, tell the recipient to use a media player to play the attached multimedia file and that free media player updates to play MPEG1 files can be obtained from Microsoft.

Sharing video on CD Compact Disc (CD) can share digital video in two ways, as a VideoCD for playback using a DVD player or for PC playback using a media player.8 Most medical professionals prefer formatting the CD for PC playback. The following steps are recommended procedures for sharing digital video on a CD for PC playback: 1. Follow steps 1–3 under “Recording and Transcoding Recommendations.” Video selections can be relatively long because the CD can hold approximately 70 minutes of MPEG1 video at this resolution. 2. Use a CD-writing program, included in the Kay Digital Stroboscope system and available on many newer PCs, to write the file created to a blank CD-R or CD-RW. 3. Tell the CD’s recipients to copy the multimedia file to their hard drive if they experience glitches when attempting to play back directly from the CD.

Making video for PowerPoint In the past, videotape copies were the medium of choice for presentation of examination results at Journal of Voice, Vol. 18, No. 1, 2004

professional meetings. PowerPoint presentations are now very much preferred. It is possible (with due regard for the limitations on image resolution and segment duration) to insert “standard” digital media files into PowerPoint presentations. 1. Follow steps 1–3 above in Recording and Transcoding Recommendations. Transcode no more than 10 to 20 seconds per example. This duration is dictated by practical considerations of loading files for presentation during a professional meeting. 2. Within PowerPoint, insert the “movie” thus created into the appropriate slide. 3. If the PowerPoint presentation is copied to a CD, make sure that the multimedia file is included on the CD along with the PowerPoint presentation. (This is important because when you “insert” a movie into a slide, you are really only telling PowerPoint to look for that particular movie file at the time of the presentation. The multimedia file is not part of the PowerPoint file, and so it must be copied separately.) 4. When presenting, copy both the PowerPoint presentation and the video file to the presentation computer’s hard drive, because the video may not play smoothly from the CD.

Sharing video on DVD-Video DVD-ROM drives in PCs can be used for reading computer data and for playing DVD-Video. Standalone DVD players do not recognize computer data but can play DVD-Video. Therefore, using a DVD-Video format allows playback on either PCs with DVD-ROM drives or by standalone DVD players. To make a DVD-Video, proceed as follows: 1. Follow steps 1–3 above in Recording and Transcoding Recommendations. However, use full resolution (640 × 480) MPEG2 and observe all of the settings required to make DVD-Video–compliant files. Selections can be relatively long, because the DVD can hold approximately 60 minutes of MPEG2 video at this resolution. 2. Use a DVD authoring program to convert, author, and write the DVD-Video standard on a blank DVD ⫹ R disk. (DVD ⫹ R has a higher

EXCHANGING DIGITAL VIDEO probability of being compatible with standard DVD-Video players than with DVD ⫹ RW.) 3. Tell the recipient of the DVD ⫹ R that this file is a DVD and can be played in PCs with DVD-ROM or DVD ⫹ RW drives. It is also playable by stand-alone consumer DVDVideo players. Sharing video on a local area network It is often convenient to be able to share a video examination with colleagues in the same practice setting over a local area network (LAN). This can be done (as always, with due consideration of limitations of selection length and image resolution) bystoring the video selection as a standard media file on the network. In order to do this, the following steps should be taken: 1. Follow steps 1–3 above in Recording and Transcoding Recommendations. Transcode a segment of no more than 10–20 seconds to MPEG1. The duration restriction is recommended to minimize file sizes. 2. Store this file to the selected network drive and directory. It is advisable and appropriate to discuss the location and file size with the network manager.

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Because of camera size and light sensitivity characteristics, it is unlikely that high-definition video (HDTV) will have much to offer laryngeal examination over the next 5 years. Digital cameras, unconstrained by NTSC or PAL limitations, may be used, but there remain technical obstacles to surmount. As medical facilities increasingly add network connections to examination rooms, and as wide-area networks with broad bandwidth proliferate, we may find that the desirability, and perhaps even the requirement, of exchanging digital video examinations via the Internet and e-mail will grow.

CONCLUSION Laryngeal examinations are increasingly recorded in digital format, usually with PCs using proprietary hardware-dependent digital formats maximized for playback quality in dedicated systems. Sharing of these examinations with other medical professionals, to be viewed on generic PCs, requires that the video files be converted to standard multimedia files with less resolution and fewer playback attributes than the original digital formats. However, even with these limitations, multimedia files are useful for sharing information about patient behavior with other medical professionals who can readily learn the procedures for sharing these files.

FUTURE TRENDS Predicting trends in digital video is loaded with all of the difficulties of predicting the future of any quickly changing technology. Despite this, it seems clear that advances in media and increasing processor speed will make computers more capable of handling digital video. At the same time, there is ongoing progress in algorithms for compressing video while preserving quality. New software standards for distribution, such as MPEG4 and the Microsoft Series 9 Media Player formats, are likely to compete with the present dominance of MPEG1 and MPEG2. It is, however, unlikely that the conflicting requirements of recording and distribution will be easily resolved in the next few years. Standalone DVD recorders, which do not yet match the quality and features of dedicated computer-based systems, continue to improve.

REFERENCES 1. Utz P. Today’s video: equipment, setup and production. 3rd ed. Englewood Cliffs, NJ: Prentice Hall; 1999. 2. Keith J. Video demystified. 3rd ed. Eagle Rock, VA: LLH Technology Publishing; 2001. 3. Taylor J. DVD demystified. 2nd ed. New York: McGrawHill; 2001. 4. LaBarge R. DVD authoring & production. Lawrence, KS: CMP Media LCC; 2001. ¨ vec JG, Schutte HK. Videokymography; high-speed digi5. A tal recording of vocal fold vibration. J Voice. 1996;10: 2001–2005. ¨ vec JG, A ¨ ram F. First results of clinical 6. Schutte HK, A application of videokymography. Larynogoscope. 1998; 108:1206–1210. 7. Baken RJ, Orlikoff RF. Clinical measurement of speech and voice. 2nd ed. San Diego, CA: Singular; 2000:402–405. 8. Purcell L. CD-R/DVD: disc recording demystified. New York: McGraw-Hill; 2000.

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