how do I reduce .mov file size

how do I reduce .mov file size

The simple answer is to make the combined total data rate of the new file less than the combined total data rate of the source file. Unfortunately, the best way to do this is dependent on how the source file was made and your specific requirements for using the final modified file—neither of which were indicated in your original posting. (I.e., File Size = Total File Data Rate x Duration of the Video Clip)

To begin with, the MOV file extension refers to the file container and not the compression formats contained within the file container. MOV is a "generic" QT file container. This means it can contain any form of compressed data compatible with the system on which the file was originally created—from text and/or still images to various forms of compressed audio and/or video data. Because of this, it is usually helpful to include information about MOV file content when posting questions like yours. E.g., you can post a QT X or QT 7 "Inspector" window image like the following:

Next, you need to understand that different compression formats have different characteristics. Some are "low efficiency" while others are "high efficiency" based on how well they compress data. The former tend to have relatively high data rates as compared to the latter. Therefore, if your source videos employ low efficiency codecs, the data can be re-exported using a high efficiency compression format having lower combined total data rates to reduce the size of the source file. For instance, in the example below, the Apple Animation video with PCM audio MOV low efficiency file was re-exported as an H.264 video with AAC audio MOV high efficiency file which reduced the source file from 2.86 GBs down to 156.60 MBs. I.e., since the combined total data rate of the exported file is roughly 1/18th that of the source file, the final export file was approximately 1/18th the size of the source file as seen below:

In cases where the source file is already using a "high efficiency" codec, the data can be re-compressed to the same compression format using lower data rate settings if you converter allows such settings. For instance, the H.264/AAC MOV file in the above example was encoded using the default QT X conversion "Higher Quality" setting. However, the QT X convert routine built into Mavericks and later versions of Mac OS X also has a "Greater Compatibility" encode option that exports the H.264 video at roughly half the data rate of the "Higher Quality" default option as seen below:

Another way to reduce the size of your output file is to reduce the dimensions of your video display. That is, there is a direct relationship between the area of your display and the amount of data required to encode the display as seen in the following example where the dimensions of the above file ("1a") is reduced from 840x480 to 640x365 (file "1b") below:

While there are other factors that influence file size (such as key frame frequency, graphic complexity, motion vectors, etc), compression format, compression data rates, and display size are probably the easiest to manipulate and provide the greatest reduction in file size for your invested effort.

Since mov file are already compressed, they can't be compressed any further.

If you want them smaller to email them, consider using something like DropBox to store them on the web and sending the link so that the recipient can download them from DropBox.