Video Formats – What you See is not always what you Get

Introduction

In this month’s look on the web, we will not discuss a single website, but rather address a topic that becomes increasingly important: video formats and their use in presentations.

You all know the problems with video files: either you have already experienced some trouble yourself, or you have met a desperate-looking colleague at a congress who is coming from the presentation preview room where he noticed that his carefully arranged presentation will not work as planned because the computer on the congress site refuses to play the video that is part of the presentation.

This journal’s internet forum also offers the possibility to upload video files; there, you find the option *.avi or *.mpeg.

What exactly lies behind these cryptic letters? What other video formats are there? What do you need to create and play video files?

This column will address some of these issues; please understand that we cannot discuss this topic in depth here, this would probably require a special issue with 100+ pages that would be beyond the scope of Clinical Neuroradiology.

For those readers that are interested in a more detailed and more technical description of the various video formats, I have provided an extensive link list. This journal has its own internet forum, so we will use the synergy between print media and digital media: this link list is found in the forum. (Another good reason to register for this forum if you haven’t already done so!)

Basic Concept of Video Files

Technically speaking, what we simply call a “video file format” is a so-called container format. These data files can hold various types of data, e.g., audio and video data together with information about their synchronization – the typical form of what we simply call “a video”.

These data are usually compressed by means of a standardized codec (compression/decompression algorithm).

Popular Container Formats

Among the numerous container formats that are in use today, the best-known, identified by their file extensions, are

• avi – which stands for Audio Video Interleaved. Popular in the Windows® world.
• mp(e)g – a format (meanwhile, numerous formats) defined by the Moving Picture Experts Group. Meanwhile, we have reached MPEG-4. (The well-known MP3 music format is part of the audio format of MPEG-1.)
• mov – identifies files associated with Apple’s “Quick-Time®”.

Another very popular format, rm (RealMedia; you will know it if you have the “Real Player®” installed on your computer), is mainly used for “streaming” data, e.g., receiving radio, TV or music over the internet. It will not be discussed here as it is not needed for a neuroradiologist’s purposes.

Playing Video Files

Watching a video on your Mac or PC that is coded in one of the above-mentioned formats is no problem – your Mac has “QuickTime®” installed as standard, your Windows PC will have “Windows Media Player®” installed. Both programs are also available for the respective other operating system:

“QuickTime” on a Mac (top; Mac OS X 10.3.8) and on a Windows PC (bottom; Windows XP Pro SP 2). Version 7.1.3. At the time of writing, the most recent edition (September 2006) is available for both operating systems.

“Windows Media Player” on a Mac (top) and a Windows PC (bottom). The latest version (V. 11, October 2006) is only available for Windows, the most recent version for Mac OS X is V. 9 (November 2003).

Looking at videos in our internet forum is no problem at all as both player programs can handle .avi as well as .mpg files.

Creating Video Files

When you create a video sequence, e.g., from angiographic images to better illustrate a procedure or technique, you should first define where this video clip will be used:

1. stand alone, i.e, you send a video file per e-mail to someone else or you send it to our internet forum, or
2. included in a PowerPoint® presentation. (I chose PowerPoint® as it is the most widely used presentation program that has become a standard for congress presentations.)

The first instance is relatively easy to handle; the inclusion of video clips in presentations, however, can cause problems.

Some PACS systems allow to generate video clips directly from the menu – you select the appropriate series, click on “Create Video,” and that’s it. Such options are also provided in the programs OsiriX®, a DICOM viewer and image processing program for the Mac that exports in QuickTime format, and DICOM-Works ®, a similar program for the Windows world that exports as .avi. The result will be a file that should run on almost any computer system.

If, however, you want to edit the images – leave out the empty “mask” in a DSA series, insert circles or arrows to highlight specific points of interest, or insert descriptive text –, things become a little more complicated.

You will probably export the DICOM images provided by your PACS as .jpg files (easy to do with the programs mentioned above), edit these, and then create a video clip from this series of .jpg images.

Numerous programs (one, 6 years old but still doing perfectly what it was supposed to do, is shown below) allow to create a video sequence from a stack of single pictures.

If you want to “play it safe,” don’t use any compression, don’t define “key frames” or whatever options your graphics program has in stock:

Screenshot from an older version (2001) of the program Animation Shop® (when it was still included with Paint Shop Pro®). I still use this program to generate .avi files.

Preparing a video clip for a PowerPoint® presentation can be easy: when you are allowed to bring your own computer for the presentation, everything will, of course, work fine – you created the video clip on this machine, you inserted it in your presentation, so you can be sure that it will run.

If, however, you are still using Windows 2000® with the corresponding version of PowerPoint®, and the congress venue is equipped with XP Pro® and Office 2003®, you may be in trouble. (This, of course, also applies vice versa.)

Some Tips for the Inclusion of Video Clips in PowerPoint® Presentations

1. Make sure that the presentation and the included video clips are in the same directory (folder) when you create the presentation.
   If you have a folder named “presentations” and another named “animations”, and you include the file on your machine from these respective positions, it will not be found when you try to run the presentation from a CD or memory stick. Have them both in the same folder, during the creation of the .ppt file and during the presentation. (Just copy the complete folder to your stick.)
2. If possible, save a video clip in different formats. If you have it as .avi and .mpg, you can still edit the presentation during the preview process – having two versions doubles your chance, having three (e.g., .avi encoded with different codecs) almost makes sure that this strange machine at the congress site will be able to read at least one of them.
3. Go for uncompressed video formats – the files will be larger, but this is no longer a problem with today’s fast computers and large-capacity portable storage devices.

Video clips can be tricky, but they will always capture your audience’s attention, so it is worth to invest some extra time in coping with different data formats!

A trademark may be legally protected even if, when reproduced in this journal, the sign ® or other indication of possible legal protection are lacking.

Christoph Ozdoba, Bern