I will assume you are using a computer, phone, or tablet. Lucky for you there is one free, open source, cross platform app that is OS agnostic about media files. (free in the classical sense: no cost, and therefore no third party interweb ads)
on mobile store search either VLC or VideoLAN
removed google evil like I have from android? Great, now install F-droid from f-droid.org, despite its snowflake admin, and search the free open source repository for VLC
linux, mac, and windows machines have VideoLAN downloads available:
even if you don't know what computer you have chances are the site will guess properly for you
The true advantage is for windows users suffering improperly configured Direct Show filters (the stuff that makes playback of media typically possible, but accounts for a wide variety of failures)
drag video into VLC or use open menu or click on video or audio file and select VLC for playback
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