Support for APK expansion files (OBB) - Unity Manual

APK expansion files are used as a solution for the 100MB app size limit in the Google Play Store. If your app is larger than 100MB (which is quite likely for a big game), you have to split your output package into the main part (APK) and the expansion file (OBB). Refer to the Android Developer documentation on expansion files for more information.

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Manually copying Unity's APK and OBB files to an Android device for