Talk:Video Production/Making subtitles in subtitle workshop

I meet a problem with opening video in mp4 format. When I open "Video > Open... >" and select f.e. Video.mp4, there I have got message: Unsupported media file Video.mp4. Why it so terrible complication? It is there need to convert this video to some another format there? I do not understand, why it may not be so easy to use it straight.