This Community Server module automatically generates preview images (thumbnails) for videos uploaded to media galleries and as attachments to other posts. The module executes FFmpeg (not included) to read the video file and extract an image, which it stores in Centralized File Storage alongside the video attachment. The preview generation module can create previews for all of the video file formats that are supported by Community Server, including AVI, MOV, SWF, MPEG, WMV, FLV and others. The module is also configurable, allowing site administrators and individual users to specify how long into a video to take preview images.
See the included README file for complete instructions about how to use of the module.