This solution was performed for LibreOffice on Windows 10, but should also work with OpenOffice.
The issue of why there is no sound is due to LibreOffice’s reliance on the Operating System to play multimedia files. This is due to LibreOffice being multi-platform and there is currently no decent cross-platform multimedia framework that works with all codec’s (coder - decoder) ‘out of the box’.
The PowerPoint .pptx file has an embedded .m4a (MPEG-4) audio file (that’s what I found with the particular .pptx file I was trying to view/hear). Thus, Windows must have the codecs installed to play the .m4a file. Windows ‘out of the box’ has limited ability to play media files and thus, they must be added.
The solution: install K-Lite Codec Pack - - go to: codecguide.com and download and install either the ‘Basic’ or ‘Standard’ package. This will add a number of codecs that will allow your Window’s box to play almost any multi-media file you encounter. You will be downloading a single .exe file, then execute (run) the .exe accepting all the defaults. Once installed, I still did not have sound until I rebooted Windows.
Note: K-Lite is freeware. There is no cost to use it. However, it’s not open source.