If Communicator is unable to play a video, it may be because the required video codec is not installed on your system. A codec is a piece of software which extracts the audio and video from a video file and in most cases it has to be installed separately from the software that is actually displaying the video. Codecs are not usually installed separately, but installed as part of a codec pack. A codec pack is a collection of codecs for a variety of video and audio formats. The recommended codec pack for use with Communicator is lavfilters. It can be downloaded from here: https://code.google.com/p/lavfilters/
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