vFilter not working?
**Describe the bug**
I would like to add a timestamp to the video, but using the vFilter option doesn't seem to do anything

**To Reproduce**
I added ```drawtext=text='My text starting at 640x360':x=640:y=360:fontsize=24:fontcolor=white``` to test this, and also tried to add ```-vf ``` before ```drawtext=..```

I also changed the ```videoProcessor``` to a local installed version of ffmpeg, does not make a difference

**Expected behavior**
The video should show a textstring

**Logs**
n/a

**Screenshots**
n/a

**Environment**
- Node.js Version: v16.13.2
- Camera UI Version: v5.0.16
- Operating System: Raspbian GNU/Linux 10 (buster)
- Browser: N/A
