A PowerPoint deck that is too big to email: shrinking it on a Mac

A shared deck has been through ten people, each pasting in screenshots and photos, and it is now 300 MB. The fix starts with knowing what inside it is heavy.

See what is inside

A .pptx file is a zip archive. Terminal can list its contents by size without changing anything:

unzip -l Presentation.pptx | sort -n | tail -15

The largest entries under ppt/media/ are the pictures and videos. That tells you whether to compress images or deal with a video.

Compress all pictures at once

1. Save a copy of the deck first.
2. Select any picture, then open the Picture Format tab and click Compress Pictures.
3. Choose a resolution such as Web or Email, tick Apply to all pictures in this file, and tick Delete cropped areas of pictures.
4. Click OK and save.

Videos

Embedded videos are stored in full inside the file. Compress them before inserting, with Finder's Encode Selected Video Files, covered in compressing video. Or link to the video online instead of embedding it.

Other things that add size

• Embedded fonts, turned on in the save options.
• Hidden slides full of images nobody uses any more.
• Pasted screenshots at retina resolution, which are twice the pixels they appear to be.

ls -lh Presentation.pptx Presentation-small.pptx

The same unzip -l check works on Word files: see reduce Word document size. Office's own caches on the Mac are covered in Office caches.