MPEG Streamclip Best Export Type

Any suggestions on what I can do with them that reduces the size, but keeps the quality?

If you don't plan to use them for editing later, you can always convert them to TV/iPad targeted H.264/AAC at 5 Mbps or less. That is about a 13:1 reduction in the data rate/file size requirements. It all depends on what you consider acceptable quality. Remember, compression is a matter of throwing away "less critical" data and there is always some loss in quality whether it is visible or not.

You started with highly compressed when the files were stored on the camera media and then "expanded" it to do editing via MPEG Streamclip.
Open one of these files in QuickTime Player and open the Movie Inspector window to tell us more about it. What codecs? What data rate?

The Motion JPEG codec isn't very good at "compressing". Think of it as an image file and thirty of them every second. It's good for editing and preserving quality but a poor choice for a "delivery" format.
The audio track isn't compressed at all. Just raw data. The total data rate is absurdly high.
I would use H.264 video and AAC audio. As Jon suggests, about 10 to 20 times smaller in files size.
The "Apple TV" preset option may be your best foolproof export. Even though the dimensions may seem small you'll be quite happy with the results even when viewing at "full screen".

I would export dozens of short clips (one minute from your source files) via MPEG Streamclip using various settings and data rates.
H.264 video will probably make the best file size versus quality. AAC audio will keep the file size of the audio track about ten times smaller than your current settings.
Choose H.264 and test with lower data rate settings first. "Half size" (540) dimensions will also reduce the total file size without reducing quality because you can then "bump up" the data rate.

First question answer is yes. Try various "limit data rate" exports as part of your tests.
Dimension is the height and width. The smaller you make then the smaller the file size will be.
All that said, video compression is more of an art form than any group of settings and only your eyes and ears will be the judge. Every video is a bit different. Fast motion is very hard to compress where "talking head" shots are the easiest.
Obviously, the higher the data rate the better the video will look. No compression would be perfect but the file would be huge in file size. Reducing dimensions is the first, most obvious, test. The display and playback would be your tests.

So, to get those settings in MPEG Streamclip, you would load the video in Streamclip, then go to "File", "Export to MPEG-4"? And then in there, select the Compression as H.264, the Sound as MPEG-4 AAC, and then click on "iTunes", and select one of the four different "Apple TV" settings? Does that sound right?

You have it a bit backwards. As soon as you open the "MPEG-4 Exporter" window, immediately press the "iTunes" button and select one of the TV options. If you start my entereing settings and then selecting an TV preset, some of your settings may be changed. Whereas, if you select one of the TV options first, any changes you make will be the ones actually applied to the conversions.

As to which "iTunes" option to select, it depends on the source dimensions and aspect ratio, as well as, your actual target use for the output files. If you actually have an TV device, you would probably want your output to be compatible with it. This means that if your source file is 1280x720 or larger and was shot at 30 fps, you would limit your selection to 960x540 because the TV specs are limited to 960x540 at 30 fps but can play 1280x720 at 24/25 fps. On the other hand, if you have an iPad you can use the 1280x720 dimensions with the full 30 fps frame rate. (I.e., it is usually a good idea to avoid changing source frame rates and/or source interlacing if possible.)

When I select an "Apple TV" setting, it has the "Limit Data Rate:" check box checked, with the text box and pull-down menu next to it. This is what you are saying I should play with a little bit to see which I like the best?

The MPEG Streamclip TV preset limits the video data rate to 5 Mbps because that is the limit the TV device is supposed to handle. This data rate should be sufficient to provide commercial DVD at 720p dimensions downscaled from a 1080i/p source file. If you are not worried about mobile device compatibility, then you could use somethiong on the order of 8 Mpbs for for a full 1920x1080 movie and achieve about the same level of quality. Just remember, the larger the scale of your output, the longer the conversion will take. Further it is generally a waste of conversion time and storage space to upscale target files larger than the source file dimensions since you cannot "create" new data the would improve playback.

As to audio playback, if you are targeting a mobile device, MPEG Streamclip will automatically limit your AAC output to a max of 160 Kbps at 48 KHz even though the "box" says 256 Kbps since this is device limit.

And dimensions are the resolution settings?

The MPEG-4 Exporter window refers to them as the "frame size."

One more thing, the size that the file will be (the estimated one next to the pull-down menu), and the file size that it is after converting it doesn't affect how the video looks? It just affects the size of the clip? Just editing the size in the Data Rate box won't do anything to the quality?

As QTKirk indicated, "good" compression is an art. To be really good, the user must use all the tools available to meet the challenge of differents scene situations in your movie. As he further indicated, things like the rapidity of motion, the number and type of vesctors involved, the amount of light, the complexity of the graphics, etc. all have an effect on compression requirements (e.g., data rate rate to frame rate ratio, key frame rate to motion ratio, etc.). So yes, the data rate, frame rante, and display dimensions are important factors here. IF you reduce the display dimensions but hold the data rate constant, the quality tends to improve since the data to target pixel ratio increases. In a similar manner, if you reduce the frame rate using a blending rather than drop algorithm and again hold the data rate constant, once again you quality tends to improve since the data to frame (and thus, pixel) ratio again increases. However, if the data rate becomes to high for the viewing device, then you begin to defeat your purpose in increasing playback quality because the player then tend to "drop" frames during playback if it can't keep up with your data throughput. This is why there is not fixed answer her and why QTKirk advised that you make test conversion to better assess "quality" in the terms of your personal work flow and method of viewing the final product.

So, if I have an Apple TV, then I would want the videos to be at Apple TV 960 x 540 setting, not the 1280 x 720? Does this apply to the newest Apple TV?

No, the new A4 TV is supposed to be able to keep up with 720p @ 30 fps (same as the iPad).

By mobile device, do you mean iPod, iPhone, iPad, etc, excluding Apple TV, or including Apple TV?

I tend to include the TV with Mobile devices as opposed to a standalone computer platform but others may not.

The larger the scale of the output, the larger the file size too?

Yes, doubling the dimensions means you have four times the display area or four time the number of pixels to be addressed.

Ok. If I just am going to have them on my computer, not mobile devices, then what should I do with the audio?

Depends on the audio compression format. If you are sticking with AAC, 64 Kbps/channel is considered "normal" with 80/Kbps be considered good quality. It us unlikely you will be able to tell much difference above 96 Kbps/channel. I am usually more interested in the channelization than the data rate and would usually prefer a 448 Kbps 6-channel AC3 file (Avg <75 Kbps/channel) over a 320 Kbps stereo AAC file (Avg 160 Kbps/channel).

What would you say that the maximum Data Rate would be for viewing them on a MBP Early 2008?

Again, it would depend on the compression used and the total Video + Audio data rate. Basically, if the picture starts stuttering due to dropped frames, your will have to cut back on the total data rate by either using more efficient compression or lowering the data limit of the content. I.e., a typical channel of Integer (Big Endian) audio would probably be be on the order of 760 to 770 Kbps per channel as compared with the previously mentioned AC3 DVD quality 6-channel data rate.

Ok, looks like there is some testing in my future, then.

This would be best. Quality is often a matter of perception. If you hear a difference and it makes a difference to you, then by all means makes the changes the best meet your needs. As QTKirk indicated, there is no one size fits all setting that can be used here. Everything depends on your target requirements and how the content is to be used. You would not use the same settings for a computer file as you would for a file packaged for playback from a DVD (a totally different can of worms).