FFMPEG exit with code 1 when audio is enabled
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**Describe The Problem:**
<!-- A clear and concise description of what the bug is. -->
Error only appears when enabling audio on cameras but goes way when audio disabled again.
**To Reproduce:**
<!-- Steps to reproduce the behavior. -->
enable audio
**Logs:**
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```
Show the Homebridge logs here.
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```

**Homebridge Config:**

```json
Show your homebridge config.json here.
Remove any sensitive information, such as your homebridge-gsh / google-smarthome token.
```
{
            "name": "Camera FFmpeg",
            "cameras": [
                {
                    "name": "Entrance Cam",
                    "motion": false,
                    "videoConfig": {
                        "source": "-i rtsp://user1:password@10.0.1.33:554/videoMain",
                        "audio": true,
                        "debug": true
                    }
                },
                {
                    "name": "DoorBell Cam",
                    "motion": true,
                    "doorbell": true,
                    "videoConfig": {
                        "source": "-i rtsp://admin:user1:password@10.0.1.16:554/Streaming/Channels/101",
                        "maxWidth": 1920,
                        "maxHeight": 1080,
                        "maxFPS": 12,
                        "maxBitrate": 300,
                        "audio": true,
                        "debug": true
                    }
                }
            ],


**Screenshots:**
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**Environment:**

* **Node.js Version**: <!-- node -v -->
* **NPM Version**: <!-- npm -v -->
* **Homebridge Version**: <!-- homebridge -V -->
* **Homebridge Camera FFmpeg Version**:
* **Homebridge Config UI X Plugin Version**:
* **Operating System**: <!-- Raspbian / Ubuntu / Debian / Windows / macOS / Docker -->

Homebridge and ffmpeg camera plugin updated today 11-17-2020

OS | OS X El Capitan
-- | --
MacBook-Pro.local
10.0.1.31
v14.15.0
v6.14.8


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