Occasionally, VLC (VideoLAN) player gives an error message about not supported "undf" audio or video format. This error message is prompted in case a proper decoder for the video format is not loaded in VLC, you just need to fix this and not convert undf to mp4, in case your .mp4 video triggers this error.
Just check for a new version of VLC player or codecs. Sometimes partially downloaded files cause this error and you might need to either finish the download in process, or download the file again.Open UNDF file Open MP4 file
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