Use Video Converter Factory, Super for Windows to transcode H.263 video format to MPEG-2 stream (Blu-Ray) file format. On Mac are available Paytube HD Video Converter for Mac.
You can also use FFmpeg command line tool, open Bash (Terminal) and type:
ffmpeg -i /path/to/your/file.3g2 -vcodec copy -acodec copy /path/to/your/newfile.m4v