Place ad images and videos into this folder.

Supported formats:
  Images: .jpg, .jpeg, .png, .bmp, .gif (displayed for 10 seconds each)
  Videos: .webm (played for full duration)

NOTE: MP4 (H.264) is NOT supported - CefSharp's offscreen Chromium
cannot decode H.264 without GPU. Convert MP4 to WebM instead:
  ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 30 -b:v 0 -c:a libopus output.webm

Files are sorted alphabetically and rotated in order.
