FFMPEG Make Video

Having downloaded FFMPEG and prepared your video (for example myvideo.avi)

ffmpeg -i myvideo.avi -r 30 -s 256x256 myvideo.roq

Will convert to .roq format for use in your map. A simple shader can be constructed which can be applied to a simple brush face.

textures/underwater/videowall
{
        qer_editorImage textures/mymap/video.jpg
        surfaceparm nolightmap
        {
                videoMap myvideo.roq
                rgbGen identity
        }
}

You'll need to put the video in the video folder (top level).