Unusually large file size of recorded video
Video record size depends not only on resolution and framerate but also on the compression algorithm - the encoder used by your phone.

I suggest you transfer a video recorded with your phone and another recorded with your friend's phone to a computer and analyze them a bit with MediaInfo.



Look for format, width, height, framerate and bitrate (probably the video quality setting affects bitrate) and if there are small differences between the two files then there may be a problem.