It can be a bewildering subject, figuring out which video formats are going to work in a presentation. It's doubly difficult when a presentation is designed on one computer, then played on another. I can't count the number of seminars I've observed where the presenter is humming and hawing about the video: "Well it worked in rehearsal..." Even Microsoft's web site has inaccurate information about choosing a video format, so what's a user to do?
Fortunately, we've done lots of research and testing on the subject. I'm focusing here on the use of video in PowerPoint and Keynote presentations to find what works reliably. But I make one assumption: that you are using current versions of the software and operating system. In Windows, you should be on Windows 7 or better and be using Office 2010 or better. In macOS, I regard El Capitan (10.11) as a minimum, running at least Keynote 6 and/or Office 2016 for Mac. You may be able to get away with less, but the degree of uncertainty and need for testing goes up.
Video Formats - Containers
The main reason why there is so much confusion around video formats is that each video has at least 2 types of format. One is the Container format and is denoted by the file ending of the video. MP4, MPG and MOV are Container formats. Most people refer to the container format, but most can hold a variety of video and audio streams that be differently encoded. An analogy might be a Word document that can contain a variety of languages. A .docx file ending doesn't tell you if it's an English text!
Video Formats - Codecs
The second format is the encoding, referred to as the Codec (short for Compression/Decompression). H.264 or MPEG-2 are both video codecs, but there are also audio codecs like MP3 and AAC. To ensure a video plays reliably in any given context, you have to have both the right container and codec formats. This is the source of the common complaint "Well, I used an .MP4 file, but it didn't work." The codec was wrong.
It's not such a big issue when all computers in a company are one operating system. If you're only using Windows, slap in a WMV file, it will work. Usually. But when a company has mixed operating systems, or when you're designing one one operating system for use on another, you have to be much more selective.
So here's my recommendation: stick with MP4 for a container format with H.264 for a codec. It is supported by most software, plus HTML5. An MPG container with the MPEG-2 codec is also reliable for desktop software. Using either of these 2 format combinations, the video will play in Keynote or PowerPoint in macOS and PowerPoint in Windows. Always.
But how do you tell what codec is used in a given file? The MP4 or MPG file ending gives nothing away.
Video Formats - Finding the Codec
In macOS, open the video file in QuickTime Player, then choose Window>Show Movie Inspector. The video and audio codecs will display beside the Format heading. Here's what you'll see with a usable MP4 or MPG file:
Windows users must install third-party software. You can use the VLC video player for this, but I prefer MediaInfo, which is focused on simply providing information. One note: MediaInfo shows the H.264 codec as AVC. These shots show the video format highlighted in yellow: