Gfxtrace from "The Talos Principle" using Vulkan fails to create video

GAPID 1.1.0
Windows 10 64-bit
Dell XPS 15 w/ 16GB RAM
Intel Integrated and Nvidia 960M
[ffmpeg-20180723-0bb5cd8-win64-shared](https://ffmpeg.zeranoe.com/builds/)

I've created a capture of the Steam Game "The Talos Principle" with the Graphics API switched to Vulkan. I had GAPID trigger steam and was able to generate a trace loading the game (appiD 257510) and played for < 1 minute before exiting out completely.

Upon completion I try to play it back as a video and it failed. The command I used was:

```
gapit video -out talos_principle.mp4
```

1. It first failed because it says it requires FFMPEG to be installed, but this wasn't listed in any documentation I could see. Please add this (or any other requirement) to the documentation.
2. Once I installed FFMPEG it seemed to fail connecting to a server

Here's a dump of my output when trying to load the trace file.
[talos_video_error.txt](https://github.com/google/gapid/files/2229372/talos_video_error.txt)