[Bug]: ffmpeg not installed
### Describe the bug

Homebridge (on Mac) running just fine. starts up.

I have 2 Nest cams

One works just fine, 2nd does not. In HomeKit it says "unreachable"

In Homebridge there are no errors until I hit the camera in HK, and then I see:

[Nest-cam] FFMPEG is not installed. Please install it and restart homebridge.

I have tried blowing away the cached accessory and restarting.... no difference.

### Debug Output

Checking for alerts on Entryway
[9/24/2021, 4:05:25 PM] [Nest-cam] Checking for alerts on Shed
[9/24/2021, 4:05:26 PM] [Nest-cam] Setting Entryway Motion Motion to false
[9/24/2021, 4:05:26 PM] [Nest-cam] Setting Entryway Sound Motion to false
[9/24/2021, 4:05:26 PM] [Nest-cam] Setting Entryway Person Motion to false
[9/24/2021, 4:05:26 PM] [Nest-cam] Setting Entryway Motion Motion to false
[9/24/2021, 4:05:26 PM] [Nest-cam] Setting Entryway Sound Motion to false
[9/24/2021, 4:05:26 PM] [Nest-cam] Setting Entryway Person Motion to false
[9/24/2021, 4:05:32 PM] [Nest-cam] FFMPEG is not installed. Please install it and restart homebridge.

### Steps to reproduce

1. see description

### Device Type

Mac mini

### iOS Version

El Capitan

### Camera Types

Nest Cam Indoor

### Bug Persistence

Consistently

### Last Working Version

_No response_