Given that "vdx" often associates with video codecs like DivX 10 and technical forums discuss Dolby Vision/HDR profiles for similar file types, this could be a "deep color" test file. These "pieces" are used to evaluate how well a screen or player handles high-bitrate video or "deep" color depths.
Knowing if it was in a professional video editor or a personal download folder could help pin down its exact purpose. vdx_10_ev.mp4
If this file appeared on your device unexpectedly, it may have been saved through a management app like the VDX Video Downloader. Given that "vdx" often associates with video codecs