Manatee

An iMovie export that is far too big to send, and how to shrink it

· 7 min read

An iMovie export is usually too big for one of three reasons: the Quality setting was Best (ProRes), the resolution was 4K because the project started with 4K footage, or the Quality was High on a long project. If you still have the project, export again at 1080p or 720p with Medium quality and Compress set to Better Quality. If you only have the finished file, shrink it to the size you need rather than exporting a second time from a low-quality copy.

What iMovie’s export settings actually control

Open the project, click the Share button in the toolbar and choose Export File, or choose File, Share, File. The dialog has four settings that matter for size.

  • Resolution. The choices depend on the project. If the first clip you added came from a recent iPhone, the project is probably 4K, and 4K is the default. A 4K file carries four times the pixels of 1080p.
  • Quality. Low, Medium, High, Best (ProRes) and Custom. Best (ProRes) writes an editing format meant for further work in another editor. It is excellent quality and enormous, often many times the size of a High export of the same project. Custom shows a slider that sets the data rate directly.
  • Compress. Faster or Better Quality. Better Quality takes longer to export and makes better use of each megabyte, so at the same size the picture holds up better.
  • Format. Video and Audio, or Audio Only. Leave this alone unless you only want the soundtrack.

Below the settings, iMovie shows a line describing the export, with an estimated file size at the end. Watch that number as you change settings. It is the fastest way to find a combination that fits before you commit to a long export.

Re-export with settings that fit

If you have the project, this gives the best result, because iMovie encodes from your original footage rather than from an already compressed file.

  1. Open the project and choose Export File from the Share button.
  2. Set Resolution to 1080p. For a phone screen or a message, 720p is often enough.
  3. Set Quality to Medium. If the estimate is still too high, choose Custom and drag the slider down until the estimated size fits.
  4. Set Compress to Better Quality.
  5. Click Next, choose where to save, and click Save.

Length matters as much as settings. The size of a video is roughly its data rate multiplied by its duration, so a ten-minute project needs twice the space of a five-minute one at the same settings. If the video only has to show one moment, trim the project first: iMovie is the right place for that.

It helps to know what a size limit asks of you. For a size in MB, multiply the total data rate in megabits per second by the length in seconds and divide by 8. A three-minute video that has to fit under 25 MB needs a data rate of about 1.1 Mbps. That is tight for 1080p and more comfortable at 720p. Bitrate, resolution and frame rate explains which one to give up first.

Shrink a file you already exported

Sometimes re-exporting is not an option. The project was deleted, the library is on another Mac, or someone sent you the finished file. macOS has two built-in ways to make it smaller, and neither lets you name a target size.

The Finder quick action. Right-click the video, choose Quick Actions, then Encode Selected Video Files, pick a lower resolution such as 1080p or 720p, and click Continue. The encoded copy appears next to the original.

QuickTime Player. Open the file, choose File, Export As, and pick 1080p or 720p. QuickTime saves a new MOV.

Both cut the resolution, which usually brings the size down a lot, but you find out the result only after the export. If you have a fixed limit, such as an email attachment cap or an upload form’s maximum, Manatee works to the number instead:

  1. Open Manatee and choose Shrink.
  2. Drop in the exported video.
  3. Type the size you need in MB, for example 24 for a 25 MB limit.

Manatee finds the quality that fits that size and writes the result as a new file alongside the original, which it never modifies. Everything runs on your Mac, with no upload. It is not an editor, so it will not trim or cut the video; if a target is unrealistically small for the length, the honest fix is a shorter video, made in iMovie. Manatee is free for 24 hours with every feature, then $9 once. The details of working to a number are in how to shrink a video to a specific file size.

Start from the best copy you have

Every lossy compression discards some detail, and compressing an already compressed file discards more. If you have both a Best (ProRes) export and a Low export of the same project, shrink the ProRes one. It is the closest thing to the original footage, so the smaller file ends up sharper than one made from the Low export would. Why compressing a video twice makes it look worse shows what the second pass costs.

The same logic applies to iMovie itself. Do not export at Low and then shrink that file further to hit a number; export at High or Best from the project, then shrink once to the exact size.

Know where it is going

The right size depends on the destination. Email services cap attachments, messaging and chat apps have their own limits, and many upload forms state a maximum in megabytes. Check the limit first, then aim a little under it, since some services count size slightly differently than Finder does. File size limits for chat apps lists the common ones.

If the video is too long to fit any sensible target, a shared link from iCloud Drive or Mail Drop in Mail sends it at full quality without an attachment limit getting in the way.

Questions

Why is my export bigger than all the clips I put in? Because iMovie encodes the whole project again at the settings you chose. At Best (ProRes), the export is almost always far bigger than the original clips. At High, a long project with a high data rate can also end up larger than the sources.

Does Better Quality make the file bigger? It is not meant to. It spends more time encoding so the picture looks better at the size your other settings produce, so the trade is export time. The estimate in the export dialog is the number to watch.

Can I choose the resolution when I shrink? Shrink works from a size: you type the megabytes and Manatee finds the quality that fits. If you need a specific resolution, such as 720p for phones, set it in iMovie’s export or with QuickTime Player first, then shrink that file to the size.