I can't get anything to recognize and mux them
That is going to be more related to the decoders used & what they do or don't do when they see "dash" in a files header.
An old version of VLC will not play DASH.
An old version of Media Info does not know DASH.
A general all purpose "video" utility, encoder, decoder, muxer... that may work well for "everything", may fail when it comes to DASH. It could be a single component in the utility, that if replaced, will allow it to work.
A current VLC will play DASH.
A current version of MediaInfo has basic
knowledge of DASH.
The same general purpose video utility, once you replace the Media Info dll with the current version, is then able to handle DASH.
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