Constant FFMPEG_HELP 

pub const FFMPEG_HELP: &str = "\
ffmpeg was not found in PATH. Install it and try again:
  Linux:   sudo apt install ffmpeg      (or dnf/pacman install ffmpeg)
  macOS:   brew install ffmpeg
  Windows: winget install Gyan.FFmpeg   (then reopen the terminal)
or set `ffmpeg = \"/path/to/ffmpeg\"` in oxframe.toml / pass --ffmpeg <path>.
PNG sequences (--format png) do not need ffmpeg.";

Installation hint shown when ffmpeg is missing.