Describe the bug

When adding video to the media tab, you just see a grey rectangle. You can post, and the video will play in the post, but not in the preview.

It's interesting to observe that VLC actually fails to play the video as well with the error message displayed below, but whatever built in video player that's in vanilla Gnome these days is able to play it. (The video is a raw output straight from Blender.)

Steps To Reproduce

1. Not sure if Mastodon re-encodes it, but you can try the video from here: https://oldbytes.space/@eobet/112568134625001023
2. Attach H264 video in an MP4 container to a post and observe the lack of preview in the media tab.

Logs and/or Screenshots

Instance Backend

glitch-soc

Operating System

Nobara (Fedora 39 w Gnome/Wayland)

Package

Flatpak

Troubleshooting information

os: GNOME 46 (Flatpak runtime)
prefix: /app
flatpak: true
version: 0.7.2 (production)
gtk: 4.14.4 (4.14.1)
libadwaita: 1.5.1 (1.5.0)
libsoup: 3.4.4 (3.4.4)
libgtksourceview: 5.12.0 (5.12.0)

Additional Context

No response