Mjpegdec.dll file is part of jpeg_dec.dll product developed by jpeg_dec.dll. It is responsible for dahuatech functionality. This part is required for jpeg_dec.dll to function. If you are planning on replacing mjpegdec.dll with a new version make sure that you backup your old file. Replacing mjpegdec.dll file with a diffent version can cause jpeg_dec.dll to malfunction.