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Computers in Radiology |
1 Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave., Boston, MA 02215.
Received October 14, 2005;
accepted after revision January 23, 2006.
Address correspondence to C.-S. Yam
(csyam{at}caregroup.harvard.edu).
Abstract
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CONCLUSION. As more and more radiology journals establish an online presence, radiologists wishing to submit journal articles with movie clips need to understand the electronic submission process. Viewing a movie clip via an online journal is different from viewing one with PowerPoint using a local desktop computer because the movie file must first be downloaded onto the client computer before it can be displayed. Users thus should be cautious in selecting movie format and compression when creating movie clips for online journals. This article provides step-by-step demonstrations and general guidelines for movie format and compression selections.
Keywords: computer movie clips • research
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The information here is aimed specifically at creating Internet-compatible movie clips for online journal publication, not PowerPoint presentations. Using movie clips in PowerPoint requires extra considerations regarding movie format and compression algorithm selections. I offered detailed guidelines for preparing movie clips for PowerPoint presentations in my previous article [1].
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Playback Speed
The playback speed of a movie clip is measured in frames per second (fps).
If a movie clip contains 50 images with a playback speed of 10 fps, the total
playing time for the entire movie is 5 seconds. Depending on applications,
frame rates between 10 and 30 fps should be optimal for most Internet-based
applications, including e-journals.
Movie Compression: Codec
A codec is a software algorithm used to compress and decompress digital
videotape or audio files. Using a codec in movie clips reduces file size. This
capability is especially important for today's multimedia applications over
the Internet where transmission of huge data files is still the most common
bottleneck issue. Currently, many of the movie clips are suitable for online
journal publications (e.g., MS AVI Videotape, MPEG Movie, and QuickTime
Videotape); however, some require specific movie viewers such as Windows Media
Player (Microsoft) and QuickTime Player (Apple). For instance, most of the
QuickTime movies (*.mov) are not supported by Windows Media Player,
and some AVI movies (*.avi) cannot be viewed by both Macintosh and
PC without installing additional third-party codec(s)
[1]. Be careful not to choose
uncommon settings for your movie clips. Similarly, MPEG (MPEG-1), a
traditional movie format developed by Motion Picture Experts Group, was once a
common format used by many media applications but is now a mystery to many
people because of the wide range of its derivatives (i.e., too many different
kinds of MPEG). For this reason, I conducted a compatibility study among file
formats, videotape codec, movie viewers, and computer platforms. Tables
1,
2,
3 present the results of this
study. You can use these tables as general guidelines for selecting movie
format and codec for your movie clips.
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Depending on journals and publishers, movie format and codec requirements for movie clip submissions may vary. As a good practice, always refer to the submission guidelines provided by the journal. For an example, Appendix 1 provides the compatible movie file formats and other types of supplemental data for online publications in AJR.
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Movie-Editing Software
Many desktop applications can be used for creating movies clips: Platypus
Animator (Snapfiles), Photo Slide Show (DigitByte Studio), and QuickTime Pro
(Apple)
[2-4].
For demonstration, I describe the essential steps for creating and compressing
movie clips from common image files using QuickTime Pro, which is a
cross-platform program compatible for both PC and Macintosh systems (currently
retails for approximately $29.99). I discussed detailed information for
installing and using QuickTime Pro in a previous article
[1]. Although the process steps
described here are based on this particular application, the basic approach to
creating movie clips can be applied to other editing software.
Note that the editing software described is only required for creating the movie clips, not for viewing them. Online readers do not need to purchase any editing software to view movie clips. Common movie viewers such as Windows Media Player and QuickTime Player are adequate for viewing movie clips. Selection of movie viewers is discussed later.
Demonstrations
For demonstration, I describe common sources for movie clips, the basic
technique for optimizing movie format and file size, and the essential process
for uploading movie files, in this case, to the AJR Rapid Review Web
site. Three types of movie clips—QuickTime Videotape (.mov), MPEG Movie
(.mpg), and MS AVI Videotape (.avi)—are used for this demonstration. All
these movie formats are Internet compatible and acceptable for online
publication in AJR (Appendix
1). Note that although I use CinePak as codec for the first two
sample movies, other codec(s) can also be selected (Tables
1,
2,
3). In my previous article, I
explained that most of the common codec(s) produce similar compression ratios
[1].
Sample Movie 1
This first example shows the essential steps for creating a movie clip in
QuickTime Videotape format from a series of 2D images. This approach is most
appropriate for academic radiologists who need to create movie clips without
special equipment such as an image-processing workstation. The movie clip used
in this example is a simple cine loop of 92 axial images obtained from a
contrast-enhanced CT angiography study using a 64-MDCT scanner (Aquillion,
Toshiba). In this example, the study images were stored on a patient CD
directly from the scanner.
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In QuickTime Pro, creating a movie clip from a sequence of images is straightforward. Select the Open Image Sequence function from the File menu (Fig. 1A). At the Open File window, navigate to the patient CD and select one of the PNG images, and then select the OK button (Fig. 1B). At the next screen, select 15 fps as the frame rate and click the OK button to load the images (Fig. 1C). By default, QuickTime Pro loads all images with equal dimensions within the same folder. After loading all 92 images into a new movie window (Fig. 1D), use the control buttons at the bottom to examine the movie content. To save the movie, select the Export function from the File menu, and then select Movie to QuickTime Movie at the Export drop-down menu (Fig. 2A). Next, click on the Options button to open the Movie Settings window (Fig. 2B), and then click on the Settings button to open the Compression Settings window (Fig. 2C). In this example, I used CinePak as the compression codec, Millions of Color as the color profile, and Best for the videotape quality. Click the OK button to start the movie creation process. Depending on your operating system and hardware configurations, the processing time may range from seconds to minutes. Using my desktop PC (Dell Precision Workstation, 1 GB RAM, 200 GB hard drive) running Windows XP Professional (Microsoft), the movie clip was created in approximately 10 seconds. After the movie was created, I opened the movie clip with QuickTime Pro to spot-check the content (Supplemental Data 1, "axial.mov"). Select the Show Movie Info function from the Window menu to view the detailed movie parameters (Fig. 2D). The file size of this movie clip is 5.9 Mb.
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The axial images were sent from the scanner to a nearby workstation using the DICOM transfer protocol for generating a 3D model. A 360° snapshot movie of the model was then exported as a movie clip onto a portable USB drive. Depending on applications and/or user preferences, creating 3D images from a workstation may be more complex and labor intensive than this example.
After transferring the movie clip from the workstation onto my PC, I checked the movie format and file size using my editing software with the following steps. Select Open Movie in New Window function from the File menu to load the movie clip. Select the Show Movie Info function at the Window menu to display the movie parameters: This movie clip was created in noncompressed AVI format. Without compression, the file size of this movie clip is nearly 96 Mb. Although this large file is still acceptable for PowerPoint presentation using a well-equipped laptop computer, it is definitely too large for online journal publications. The easiest solution for reducing file size is to apply a compression. Select the Export function from the File menu, and then select the Movie to AVI for the Export option. Click on the Options button to open the AVI Settings window, and then click on the Settings button to open the Compression Settings window. Enter the same parameters as in the previous example (i.e., CinePak, Millions of Colors, and Best). Click the OK button to start the conversion process. The file size of the converted movie clip is reduced to 4.5 Mb (Fig. 3, Supplemental Data 2, volume.avi).
Similar to the previous example, be careful not to display any patient information in the movie clip. Based on my experience, disabling on-screen annotations at the workstation while preparing the movie clip is the most effective and easiest way to prevent this issue.
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Uploading Movie Files
Uploading movie files to the online AJR Rapid Review Web site is
similar to uploading TIFF images. However, movie files must be uploaded on the
first page as supplemental data on the submission form. Currently, up to three
supplemental data files can be submitted. In my case, I uploaded the three
sample movie clips (i.e., axial.mov, volume.avi, and cathlab.mp4) as
supplemental data files. Similar to figure legends, I provided a separate
index page in the manuscript for descriptions of each of the supplemental
files. This index page is usually searchable and makes the supplemental data
accessible without having to go through the actual article (Trafton D,
personal communication).
Viewing Movie Clips
Movie clips are available for viewing only on the online AJR
journal Web page, not the PDF version. The Web links for movie clips are
provided in two different places. At the Search Result page, the Web link
appears on the right of the Search Result column with descriptions of the data
file (e.g., "avi file for Fig. n")
(Fig. 5A)
[7,
8]. The same Web link will also
appear at the top right of the full article Web page
(Fig. 5B). For this particular
article [7], three AVI movies
using "MS Videotape 1" codec are provided—1b.avi (4.6 Mb),
1d.avi (4.2 Mb), and 1e.avi (4.4 Mb).
Movie clips are viewed in the same way as viewing the PDF article by clicking on the PDF Web link. However, unlike PDF files that must be opened in Acrobat Reader (Adobe), movie clips are displayed in a movie viewer. Depending on your computer platform, operating system, Web browser setting, and the movie clip format, different viewers may be launched (see Tables 1, 2, 3).
If the movie viewer is not present but required for a particular movie clip, installation of the viewer is necessary. For instance, if a movie clip was created in QuickTime (CinePak codec) and your PC (Windows XP) does not have the QuickTime Player installed, the Web browser will prompt you to install the QuickTime Player (Fig. 6A). For this particular case, click on the Install button and then follow the screen instructions to complete the installation. This may also happen to Windows Media Player, especially when a newer version is required. Based on my experience, installing this type of media application does not generally harm the computer. However, some companion applications such as iTune for QuickTime Player and MSN Messenger for Windows Media Player may be installed automatically. If the companion application is not useful, remove it. Go to Start, then Settings, Control Panel, and Add and Remove Programs. Select the item, and then click the Remove button to remove the application. Also, depending on your Web browser settings, some movie viewers (such as Windows Media Player) can be embedded within the browser window as a Media Bar (e.g., Internet Explorer SP1). To restore the viewer back to a standalone application, the browser settings must be changed. In Internet Explorer, click the Media icon on the toolbar to open the Media Bar. At the bottom of the Media Bar pane, select Media Options, point to Settings, and then click Play web media in the Bar to clear the check mark (Fig. 6B).
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Choosing Movie Viewers
Windows Media Player currently is the default movie viewer for PC, and
QuickTime Player for Macintosh. These two applications are similar in terms of
viewing movie clips (i.e., they both provide VCR buttons at the bottom for
controlling movie playback). However, some noticeable differences are apparent
in the user interface. First, Windows Media Player allows a full-screen view;
QuickTime Player does not (Fig.
7A). Second, QuickTime allows real-time scrolling of the movie
frames; Windows Media Player does not (Fig.
7B). In other words, when the timeline button is dragged,
QuickTime provides instantaneously update of the movie similar to scrolling
through a stack of CT images in PACS. In addition to these two viewers, many
other applications (shareware or freeware) can also be used for viewing movie
clips. Real Player (Real Networks) is one example. This application is similar
to the other two but with a different user interface. You can download the
free versions of each of these three applications to evaluate them
[9-11].
Note: Installing Windows Media, QuickTime, and Real Players will not harm the
computer but only guarantees that more movie formats can be viewed (Tables
1,
2,
3).
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Based on my experience, the first four options are most appropriate for reducing file size without sacrificing the output resolution. Although currently, no limitations on file size for movie clip submission to AJR are cited, I believe a file size of 5-6 Mb should be appropriate.
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Similar to the increasing trends of online journal submissions, many radiologic societies such as the American Roentgen Ray Society (ARRS), European Congress of Radiology (ECR), and Radiological Society of North America (RSNA) are now steadily converting scientific exhibits and posters into an electronic presentation format at their annual meetings. Although this format is similar to the traditional desktop PowerPoint projection, the presentation mechanism is significantly different. Presenters should be cautious when using movie clips in their presentations during this format shift. Using incompatible movie clips or having broken links to the movie files may cause unexpected disasters in their presentations. For this particular reason, I will discuss the use of animated GIF files and Macromedia Shockwave Flash in my next article.
Although animated GIF and Macromedia Shockwave Flash are not technically categorized as movie clips, they both have the capabilities for displaying dynamic data sets (multiple images). Unlike traditional movie clips (i.e., AVI, QuickTime, and MPEG), these two special types of media files are embedded within the PowerPoint presentation file, not "linked." With this advantage, dynamic data sets can be securely displayed in PowerPoint without the common issue of missing file links for movie clips. These two types of files are most appropriate for e-presentation and desktop projection.
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  C.-S. Yam A solution for using dynamic data sets in electronic presentations. Am. J. Roentgenol., August 1, 2006; 187(2): W218 - W226. [Abstract] [Full Text] [PDF]
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