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What is the AAB file for Android, and How is it different from APK?


What is AAB file for Android and How is it different from APK?

What is the AAB file for Android - Since Android started more than ten years ago, APK files have been THE universal format for apps. Whether the developer or user, whether Google Play Store, APKMirror, or EFNet loaded, always APK. AAB is now mandatory for developers and a more complicated APK for Android users.

AAB obligations will apply to all new applications from August 2021. Developers can still upload updates for existing apps in APK format, so nothing has changed here for now.

What is an AAB file?

"AAB" stands for Android App Bundle. The entire code of the Android app program is stored in the AAB file. As soon as the development is complete, the developer uploads the app from now on in AAB format to the Google Play Store and, you load it from there to your smartphone as usual.

At first glance, nothing has changed, and even at the second glance. Because if you click "Download" on the Google Play Store, your smartphone will still download the APK file.

What's the difference between an AAB and APK file?

Bespoke AAB files

The difference between APK and AAB files is what they call resources. In an application, a resource is everything that is not programming code, such as images, sound files, or music. If you now press the app's "Download" button on the Play Store, Google will send you an APK file of an AAB file created specifically for your device with only the resources you need.

Does your smartphone only have full HD+ resolution? Then you get an APK without 4K material. You may not need Suomi. With the help of Google bundletool, AAB files can also be converted locally into APK.

Signing by Google, not developers

Another big difference is the app signature. In the past, it was always app developers who signed it with their developer key. This key can be used during installation on your smartphone to check if an app has been compromised and contains malware, for example, or has been enabled for other paid features.

In the future, it's not the developer who signs the APK but Google that is when creating the APK file from AAB. Logically, the key no longer lies with developers but on Google.

Are AAB files better than APK?

Smaller file size than APK

The first significant advantage of AAB files is obvious: APKs generated in this way are smaller. An average of 35 percent should be saved this way, Google wrote in October 2018. At first glance, it doesn't sound like much, but including a lot of updates for the app at some point can be depressing.

Better protection for applications

Another benefit, especially for developers, is better security. It may be more challenging to modify the app in the future. The mod scene may not be enthusiastic about it. Who knows, maybe this will reduce the number of cheaters in AmongUs, although so far, I do not believe.

Incidentally, with AAB, the Lite and Pro versions on the Play Store are also likely to die. It used to be possible to install the paid pro version after purchase, thanks to the same signature, as an update of the lite version. This is no longer possible with AAB and Google signing instead, and developers should turn to in-app purchases. 

Easier updates & development

If the APK are assembled individually depending on the user or their hardware, this has advantages for developers. As NDTV reported, thanks to the AAB format update can be played to certain devices at any given time. This is an advantage, especially with android fragmentation which is very large and can prevent future broken updates or reduce the effect.

Developing yourself will also be more accessible. In the past, many developers have uploaded multiple versions of their app APK to the Play Store tailored to different regions, languages, or processor architectures. In the future, developers will only need to upload one universal AAB file.

Are AAB files worse than APK?

AAB files and sideloading clutter

However, there are also drawbacks, mainly due to the signatures mentioned above. You want to download the new WhatsApp beta via APKMirror and try out the new features? Forget it because APKMirror uses a different signature here from the Google Play Store. Sideloading apps in various third-party app stores could be a nightmare in the future.

Of course, all you have to do is uninstall the app and reinstall it on your smartphone from another source. But then you have to depend on the application with little effort backing up all the data and then importing it again. 

AAB gives Google power

The fact that the signature will be with Google in the future can also be seen critically. If the server here ever gets hacked, all the apps suddenly become insecure. And as explained by colleagues from XDA-Developers: With the developer key, Google also has the power to change its own apps. If, in theory, the government had to put a thumbs up on Google, the back door could be built into a secure messenger without the developer's knowledge.

Google attaches great importance to security. And yes, Google is withdrawing from the market rather than subject to the morally dubious wishes of local governments. But one thing is certain: Google is gaining more power with AAB files. There is also an interesting discussion on this topic in StackOverflow.

Bug fixes become more complex

Another disadvantage concerns the developer of the app itself and the bug fixes, as developer Mark Murphy wrote in Commonsware. If one user has a problem with an app that cannot be reproduced for developers, for example, there is a simple way to date:

  • Adapt the app.
  • Send it to the user.
  • Let them update the app with it.
  • I hope that the error is lost.

However, this is only possible because developers can sign the app themselves. 


The bottom line is that the obligation to use AAB shouldn't change much for most users. Otherwise, we'll be aware of something. After all, many of the top 1000 apps on the Google Play Store have been uploaded by their developers as AAB - although there's no obligation to do so. 

But the AAB format can ruin Android fun for enthusiasts, hobbyists, and one or the other developers. After all: Google is not Apple, and it is still possible to certify apps outside the Play Store. Google has not (for now) stopped sideloading. But Mountain View is working hard to strengthen the Monopoly Google Play Store.


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