HDR10/Dolby Vision MP4 - Container (mis)identified as MOV?

[forbis]

Not sure about the "MOV" part.  m4v is an Apple proprietary implementation of MP4, so maybe that is why?

When transcoding, any MP4/M4V container appears as MOV in Chrome browsers. However, if transcoding is done in Firefox, it will display as MP4.
https://github.com/jellyfin/jellyfin-web/issues/6539

That github issue is very similar, but one thing that is different in my situation is that the "Media info" screen displays the container as mov, even when not playing. And again, on Android I get direct play and the container is ID'ed as mp4 (https://imgur.com/a/leDgIEs)

There has to be an overlap between container and codec support.  From what I'm reading, Chrome supports H264 in m4v, but not HEVC?  Which is why it is remuxing to MP4, if this is correct.

Not sure about the "MOV" part.  m4v is an Apple proprietary implementation of MP4, so maybe that is why?

I did try with .mp4 extension instead of .m4v, and had the same results. I re-examined ffprobe output for this file and one that is ID'ed properly and did find a difference in "compatible_brands" - "mp42iso2mp41" vs "mp42dby1iso2mp41". This has to play a part in this, right?

Direct plays - Identified as mp4:

Code:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '.\Green Book (2018) - [2160p HDR].m4v':
  Metadata:
    major_brand    : mp42
    minor_version  : 512
    compatible_brands: mp42iso2mp41
    creation_time  : 2025-04-06T04:55:13.000000Z
    title          : Green Book (2018)
    encoder        : HandBrake 1.9.2 2025022300

vs
Remuxes on Chrome - Identified as mov:

Code:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '.\Transformers One (2024) - [2160p HDR].m4v':
  Metadata:
    major_brand    : mp42
    minor_version  : 512
    compatible_brands: mp42dby1iso2mp41
    creation_time  : 2025-04-05T04:37:07.000000Z
    title          : Transformers One (2024)
    encoder        : HandBrake 1.9.2 2025022300