When I started making videos and putting them on the internet, I was averaging file sizes on the order of 5Mb, the movies were tiny (320x240 pixels) and their quality sucked. Now I think I am averaging close to 1Mb, the movies are generally bigger (400x300 and 480x360 pixels are my sizes of choice now) and the quality is much better. There is a lot you can do to make good movies which take up as little bandwidth as possible. In this section I will just list a series of tricks, in roughly the order I discovered them.
I tried to export my first video to quicktime format from imovie. Being adventurous, I chose the "expert" settings. First thing imovie wanted to know was how big (in pixels) I would like to have my video. Well, it is obvious that the smaller the dimensions, the smaller the final file size will be. The most important point to note is that you should maintain the 4:3 aspect ratio of the width to the height. In other words, if you want the final video to be 320 pixels wide, the height should be 240 pixels. (320:240 = 4:3). Good sizes seem to be 320x240, 400x300 and 480x360.
This is a tough subject. I will present this subject peppered with lots of hindsight. Codec stands for compression-decompression algorithm. When you export your video, you export it in some sort of compressed code which the player will recognise. When the player receives the file, it interprets the code, effectively decompressing it and plays the video for you. The trouble with codecs is that there are a lot of them. Good ones, bad ones, standard ones, non-standard ones, lossy and not so lossy ones, the list is endless. To add to the complexity of the problem, different players recognise different codecs and different versions of the same player recognise different codecs. As someone invents a better algorithm, so the next version of the video player will support it. For example: QuickTime 5 recognises Sorenson 3 codec (my current favourite) while QuickTime 4 does not. Latest news I have suggests that Apple and the MPEG 4 people have settled their licensing dispute. Thus when QuickTime 6 is released later this year (2002), it should support MPEG 4 codec which will probably be the best codec out there.
It is impossible in this small space to list each QuickTime supported codec and what it is good at. Every codec has its strengths and weaknesses. Best search for information on the internet - there is plenty. I used to use H.263 codec. I then switched to Sorenson and then Sorenson 3. If QuickTime 6 supports MPEG 4 I will almost certainly switch to that codec in the fullness of time.
American digital video cameras film using a standard called NTSC. The footage is shot at 30 frames per second (30fps). (Actually it is 30fps with one dropped frame every minute. This works out at 29.97fps, but this is the basic tips section, 30fps is close enough.) The rest of the world uses PAL which is filmed at 25fps. I will discuss NTSC, but you can transfer all the discussion to PAL with a little common sense.
When you export your video to QuickTime, you must choose a frame rate at which the video will be encoded and played. Obviously the higher the frame rate, the larger the final file will be. If you encode at 15fps, the encoding process will take every second frame and drop every other frame, in effect halving your file size. The motion will appear slightly jerky, but not too bad. If you choose 10fps, the encoding process takes every third frame and drops the other two. It is good to choose a frame rate which allows a regular number of frames to be dropped. For example, choosing 12fps, the encoder will sometimes drop one frame and sometimes drop two frames in a row. The resulting motion looks slightly uneven. You can choose fractional frame rates. For example, 7.5fps tells the encoder to take every fourth frame and drop the other three. As inhabitants of the USA like to say: "You do the math..."
In sum, reducing the frame rate is one of the best ways to make your video files smaller.
When you choose the codec and frame rate, you will generally encounter an image quality slider which gives you a range of quality from "best" to "low" or "poor". This can have a significant effect on the final file size. I generally choose something between "medium" and "low" depending on how much clarity I want in the final video. I would recommend almost never going above "medium". The return on better image quality is vanishingly small and the file size sky-rockets quickly. This comment is codec dependent though. So, take it with a pinch of salt.