Microsoft has made available STAMP (Sub-titling text add-in for Microsoft PowerPoint), a free add-in for PowerPoint that enables you to create captions for video and audio files within your PowerPoint presentations. In addition to manually adding captions, you can also work with any media files that have associated Timed Text Markup (TTML) files. This add-in lets you import the TTML files directly into your presentation. If you don’t have a TTML file, you can still add captions directly in your presentation. Having said so, TTML captions allow some extra niceties since they can be easily formatted to use text color, text alignment and other styling elements for the captions.
This add-in works in PowerPoint 2010, 2013, and non-Office 365 versions of PowerPoint 2016. All these are versions that run on Microsoft Windows.