Doing advanced optimization to further reduce your app’s size
Optimize your app’s asset files, adopt on-demand resources, and reduce the size of app updates.
Overview
Following the basic optimizations described in Doing basic optimization to reduce your app’s size is a good way to decrease the size of your app. However, you can optimize your app’s size further to minimize its footprint on a device and provide a fast download, installation, and update experience.
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Optimize your app’s asset files
Assets often make up a large portion of an app. Consider the following optimizations:
Use the most efficient image and video format possible. Image and video assets are common contributors to large app sizes. Using a more efficient image file format is a good way to reduce your app’s size. For example, consider using the HEIF format for images, and the HEVC format for videos. If you’re using PNG files, consider using 8-bit instead of 32-bit PNGs. Doing so can decrease the image size to a quarter of the original size.
Compress images. For 32-bit images, using Adobe Photoshop’s “Save for Web” feature can reduce the size of JPEG and PNG images considerably.
Compress audio files. As a general rule, compress audio using AAC or MP3 codecs, and experiment with a reduced bit rate. Quite often, a 44.1 kHz sample rate isn’t necessary, and a lower bit rate clip won’t result in a perceptible drop in quality. Learn more about optimizing your audio assets by watching Audio Development for Games.
Reduce the size of app updates
Instead of always downloading the whole app when an update to the app is available, the App Store creates an update package. It compares one or more prior versions of your app to the new version and creates an optimized package. This package contains only the content that has changed between versions of your app, excluding any content that didn’t change.
This comparison looks at everything in the application bundle, including the application executable, storyboards, nibs, localizations, and other assets, like images.
Consider the following to reduce the size of your app’s update package:
Don’t make unnecessary modifications to files. Compare the contents of the prior and new versions of your app with
diffor another directory comparison tool, and verify that it doesn’t contain any unexpected changes.Store content that you expect to change in an update in separate files from content that you don’t expect to change.
Adopt on-demand resources
Analyze all of your app’s assets and determine which resources it uses infrequently. Group the infrequently used resources into asset packs. When you upload your app to App Store Connect, asset packs don’t become part of your app’s initial download or app updates. Instead, the app can download them separately as needed. See the On-Demand Resources Guide for more information.
If you can’t adopt on-demand resources, consider implementing a web service that provides them, and download them in the background as needed, using URLSession. To learn more, see Downloading files in the background.
Leverage app thinning
App thinning is a technology that ensures that an app’s IPA file only contains resources and code that’s necessary to run the app on a particular device. Apps that are available in the App Store, and that you distribute to testers using TestFlight, already leverage app thinning. However, if you distribute an in-house enterprise app, or distribute your builds to testers without using TestFlight, you must enable app thinning when you export your app. To use app thinning:
Archive your app in Xcode.
Select the archived app in the organizer window, and click Distribute App.
Export your app using Xcode, and choose “All compatible device variants” for app thinning in the export sheet. If you support only a limited number of devices in your app, select the ones that apply.
To learn more about app thinning, see Distribution Options and watch App Thinning in Xcode.