Demuxer doesn't accept a file list

**Describe the bug**
If you attempt to use the demuxer feature of ffmpeg it breaks. Passing the file list doesn't work. It does not accept the same file format, e.g. `file path` on each line.

**To Reproduce**
Steps to reproduce the behavior:
1. I'm not going to type out the steps to use a basic feature. Read the FFMPEG manual if you don't know how to use the demuxer

**Expected behavior**
A clear and concise description of what you expected to happen.

**Screenshots**
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**Desktop (please complete the following information):**
- OS: [e.g. iOS]
- Browser [e.g. chrome, safari]
- Version [e.g. 22]

**Smartphone (please complete the following information):**
- Device: [e.g. iPhone6]
- OS: [e.g. iOS8.1]
- Browser [e.g. stock browser, safari]
- Version [e.g. 22]

**Additional context**
Add any other context about the problem here.