Do you have any software you can use? Or would you like to have some free software recommended. You gave us very little information to work with, that's maybe why no one has answered yet.
If you have Apple Compressor, use any preset that will not reduce the resolution and encode the video in H.264 (for example a videosharing-Preset). Then tweak the video bitrate so you end up with a file below 2GB.
If you don't have a conversion tool and don't want to spend money, I would do the following: Get
Handbrake to convert your video. You will end up with a .mp4 file. If you need a .mov container, just use
this little tool I programmed to change the container without reencoding (same size, very fast, no quality loss).
For both methods, you will have to set the average video bitrate accordingly to end up with 2GB. That requires some math.
1. Your video is 21 minutes long. That's 21*60 = 1260 seconds.
2. If you have stereo audio channels, I assume you will end up with 192kb/s for the audio stream. That's ( 192kb/s * 1260 s ) = 241920 kb. 1 Byte is 8 bit, so that gives you ( 241920 / 8 ) = 30240 kB. That's ( 30240 / 1024 ) = 29.53 MB for the sound. Let's say 50 MB, to be sure.
3. You get the point? Do the same for video, but the other way around:
1950 MB
=> (1950 * 1024) = 1996800 kB
=> (1996800 * 8) = 15974400 kb
=> (15974400 kb / 1260 s) = 12678 kb/s
I would try 12500 kb/s as setting for the average video bitrate.
This video explains how you can set the bitrate in Compressor and where it will show the the resulting file size. In Handbrake, setting the average bitrate is pretty self-explanatory, but you will have to wait and see how big the file is gonna be. Unless someone did the math for you.
Next time, try to give a little more information about your problem (resolution, number of audio channels, software you use/have, etc...) and more people might be inclined to help you if it's an emergency.
