Android is an open source and the Android Open Source Project (AOSP) allows users to explore the source for Google's mobile platform, modify and build it to fit their needs. You should know where to look through hundreds of new AOSP code commits to check out what's new in Android 4.4.1.

All the new stuff have been sorted out and aggregated, their descriptions and categorized them by project. The latest changelog shows every change made from Android 4.4 (build KRT16M) and Android 4.4.1 (build KOT49E). Most of the changes involve some serious development for the Nexus 5 sound performance and camera improvement.

Here's a quick list of all the Android 4.4.1 changes for Nexus devices. Note that these aren't necessarily bug fixes:

- Nexus 5 users have complained about a low sound output in some apps and this has been fixed in 4.4.1.

- The Nexus 5 camera got a performance upgrade.

- ART bugs have been fixed. These should solve all issues with WhatsApp not properly working with ART.

- The Nexus 5 haptic feedback has been tweaked.

- The Nexus 5 default mail client not syncing properly has been fixed.

- The immersive mode that reportedly breaks while adjusting the volume level has been fixed.

- The default Gallery app now is the new "Photos" app.

- The Nexus 5 benchmark performance has undergone a slight improvement.

- The transparent status bar that reportedly turns opaque sometimes has been fixed.

- The navigation bar is now transparent on the Nexus 4 lock screen.

- The Settings icon in Quick tiles has been tweaked.

- The Miracast setting has been renamed to "Cast" setting.

The Android 4.4.1 update has started rolling out to the Nexus 5, with Nexus 7 LTE and Nexus 4 following closely behind.

CyanogenMod also discovered something quite disappointing and interesting at the same time. Patches in Android 4.4.1 bear some new API (Application Programming Interface) that can be used for broad mirroring of Android to Chromecast. At this point, mirroring Chrome tabs is only the officially supported beta method. It is discouraging that API documentation said it not for third-party application use, an implication that it is only for OEM's or Google's use. Everyone still hopes that Google will open this feature in the future, though.