Overview Description:
I downloaded Celluloid v0.27 from Flathub. When I opened my videos (mp4), I couldn't hear any sound. I tried about a dozen videos and none of them had any sound.

I then tried some mp3 files and all of them played without issue. I can hear audio. So, I tried my videos again, but still no sound.

Then, I downloaded the "Big Buck Bunny" webm and mp4 trailers from here. When I opened the webm version, it still didn't have any sound. Then, I opened the mp4 version and finally(!!!) it had sound. Then, interestingly, when I opened the webm version again, it now had sound. So I tried my other videos that didn't have sound before and, for some reason, they all played with sound now.

Steps to Reproduce:

1. Install Celluloid v0.27 from Flathub.
2. Download and play the webm version of "Big Buck Bunny" trailer from here. (I'm not really sure if playing this file will reproduce the issue. Unfortunately, I cannot share my personal videos.)

Actual Results:
Videos play without any sound.

Expected Results:
Videos should play with sound.

Version:
0.27 Flatpak

Additional Information: