I'm using the GoPro Studio software, in addition to Adobe Premiere Elements which I intend on using in this case post-trimming/cutting of my video to keep it as a 2.7k file for now. When I say "cut" I mean I removed the first couple of minutes of the video and removed the last couple minutes of the movie. It went from being say a 10 minute movie to a 6 minute movie. It was filmed with my GoPro Hero3+ at 2.7k settings, medium, low light. The original file was an avi, and the new file is an avi, everything looks like it has been kept at the same resolution, etc. Where has that extra 11GB come from after doing a simple cut? I literally kept everything else the same as it was.
"The GoPro CineForm codec was designed to provide very high performance, and very high visual fidelity. Part of the technique we employ is to allow the sizes of the files to grow compared to the source. This creates lots of “headroom” for manipulating your source material in post. It is this extremely high fidelity that has allowed the GoPro CineForm codec to be used by major feature film post production facilities and studios.
So how large will your Cineform files be? Generally about 5X to 8X the size of your original mp4 files.The GoPro CineForm files are about 10% the size of what the file would be if it was un-compressed."
If you have no idea about how to use GoPro Studio to cut AVI file, why dont you simply download some video cutter from web. There are lots of options for you.
Few i can suggest you is a top guide on how to cut AVI video. It also supports trimming almost all kinds of video files like MP4, MOV, WMV, MKV, ASF, FLV, MXF, AVHCD, MTS, MOD, WebM, OGV, 3GP, etc. It is a real time saver. Love it.
Some people said Windows Movie Maker is also a nice choice, just give it a try.