: By default, many Windows systems hide known file extensions. A user might see "Dance Party.mkv" and assume it is a video, while the full name is actually Dance Party.mkv.exe .

is a more universally compatible container used by almost all hardware players and web browsers.If "Dance Party.mkv.mp4" is a legitimate video, it is simply an MP4 file where the user (or a conversion script) forgot to remove the original extension during a format shift. Cultural Legacy

is an open-standard container known for holding unlimited tracks (video, audio, subtitles).

During the peak of LimeWire, Kazaa, and early torrenting, users often encountered files like "Dance Party.mkv.mp4."

The "filename.ext.ext" format is a well-known tactic used by malicious actors to hide the true nature of a file.