For selected cameras, timelapse recordings for the last 24 hours.
The files in that directory are updated at the end of each hour.
If your Windows/Mac/whatever video software can't handle the mpg format, download the open source VideoLAN client (VLC). You can right-click on the .mpg file you want, save it to your desktop, then open it with VLC. Note these are moderately big files, give it a sec to download.