see
http://endlessgeek.com/2014/03/batch-convert-iphoto-videos-mp4/
It uses handbrake.
Best way is to experiment manually with a handful of videos and watch out for compression artefacts (the color-bleed-out blocks on faces and other smooth color transitions). When you are satisfied, create a profile with the settings, name it e.g. MyProfile. You can use these settings by invoking the cli version of handbrake inside the batch script with --preset="MyProfile"
Where or how do you store the originals?
Don't throw away information lightheartedly. This is what you do when compressing.
I copy the original folders of my canon camera manually to my external drive, additionally to importing stuff to iphoto.
So iphotos videos are rather.... dependable.
I will modify the script to directly access the originals inside the photo library. This a really bad thing to do, normally.
If you want try to contact me 1'2016. appstackex-imov4m.hofma at the service 0ox with domain .com ;)
If you try this, too, please backup before tampering with the package!
Read http://osxdaily.com/2015/04/22/show-original-file-from-photos-app-mac-finder-osx/ to see the part/video where they open the package in finder.
In finder, you can locate your library, for me and just e.g.it is:
~/Pictures/Fotos-Mediathek.photoslibrary/Masters/
(photoslibrary is the new one since migration of the iphoto database to photos database. Just look in finder, right-click "open library content" or whatever the menue entry reads in english, might be "packet content" (it is "Paketinhalt anzeigen" for me) then open the subfolder "masters", and drag the masters-folder to terminal, then you have text on the command line representing the correct location...
When you do a change directory to the path of masters, you can thereafter find all originals, e.g. by:
find . -type f \( -iname "*.mov" -o -name "*.mp4" -o -name "*.jpg" \)
This is nice for me, because I have a bunch of empty folders in this directory structure created by iphoto / photos. Find does show only results with a nice relative path.
I found if you leave all the folders starting with Printing... and the Assets folder that are in the /Library/Application Support/iPhoto/Themes folder, you can still print.
Just delete all the other folders and you will regain a chunk of disk space.
Best Answer
No, it does not compress it, but the size of the library is in fact different:
The iPhoto Library is not a monolithic file, but a so called bundle (a folder disguised as a file). If you call file > Info (cmd-i), then it's size needs to be calculated, it's subfolder and files can be seen by the usual developer tools.
So, from the POV of time machine, or the file system in general, the iPhoto library is a huge folder with thousands of files.
Now comes another issue into play: Storage media are organized in file sectors of fixed size. The size a file takes on disk is not the number of bytes of this file, but the number of sectors which the file occupies by the number of bytes per sector. The sector size usually depends on the specific file system and media capacity.
Even a 1-byte file takes one sector, so on a hard drive the smallest file size might be 4 KB, on a flash drive 16 kB.
In consequence that means that the sector size of the medium you save to has a huge impact on the overall size of your iPhoto library. I take an educated guess that the sector size of your SSD is bigger than on your backup drive.