Do you use 64bit windows OS? If yes, please click Evaer menu "Tools > Options" > "Advanced" tab, then disable the "Enable DS video stream(for 64bit system only)" option.
By default, it will create one mp3 audio file and one mp4 video file(the video file include the audio and video image) for each video calls. You can enable the "Auto-detect calls(video call recording into MP4/AVI.....)" option(at Evaer menu "Tools > Options" > Advanced tab) if you want to create only one file.