lIvecode on Microsoft Windows uses DirectShow (in LC 9.6.x) which has limited CODEC support (meaning there are a limited number of file media file formats and internal encoding of audio and video data that are supported under DirectShow). Livecode on macOS uses Apple Video FOundation (AVF) which comes with a much wider range of CODECs, so media files that play on macOS may not play under Windows. [NOTE: there are formats that are specific to each platform as well.]
We recommend/require our customers to also install the free
LAV filters on WIndows (
https://github.com/Nevcairiel/LAVFilters/releases). This a free set of additional CODEC for DirectShow that mostly provide parity between formats supported under macOS and Windows.
With some release of Livecode 10.0.0, LC is switching from DirectShow on Windows to Windows Media Framework (WMF) which also has more of a parity between formats supported across platforms, at which point a 3rd party set of CODECs like the
LAV Filters will no longer be needed.