MKV (Matroska) files are an open source file format that contains both audio and video files.
Open Broadcast Suite (OBS) uses them by default. Apparently they are resilient to problems whilst recording.
If you need to extract audio / video files from MKV files, mkvtoolnix is an open source tool and can be found at this link.
Or, you could try Video Solo Video Converter (its free for short clips) to convert from MKV to MP4 files. Adobe Premier Rush is good for formatting your MP4 videos for the various social media platforms.