Zombie ffmpeg processes running up CPU usage.
**Describe The Bug:**
Sometimes an ffmpeg process won't terminate after exiting a live camera in homekit app causing multiple extra running processes, taking up cpu.

**To Reproduce:**
One way to reproduce is to open a live camera view and quickly exit before it loads in. Another is when you go to change the volume, sometimes notification center is engaged and it cuts off the stream and when you load back in there are now 2 processes of ffmpeg running. Exiting properly there is still a leftover process. 

**Expected behavior:**
The extra ffmpeg stream should be terminated accordingly.

**Logs:**
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**Screenshots:**
Running `htop` or `ps` in the terminal reveals the many zombie streams running. I'm having this same problem with the Ring plugin. Zombie IP camera streams use over 50% of the cpu on my Synology making it so opening new streams says no connection.

**Environment:**

* **Node.js Version**: 12.16.2
* **NPM Version**: 6.14.4
* **Homebridge Version**: 1.0.3
* **Homebridge Camera FFmpeg Version**: 0.1.17
* **Homebridge Config UI X Plugin Version**: 1.0.3
* **Operating System**: Docker


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