What is Android 9.0 ?
Android 9.0 is also the operating system developed by Google. It was first published on January 25, 2018.
In February 2018, the initial code for Android 9.0 was designated Pistachio Ice Cream, and Chinese was temporarily translated as pistachio ice cream. 
On the morning of August 7, 2018 Beijing time, Google officially released the Android 9.0 official version system, and announced that the system version Android P was officially named code "Pie".
On January 25, 2018, after the announcement of the Developers Conference, Google’s developer service Twitter posted a binary code that directs users to the official website of the Google I/O Development Conference. You will see a Google Street View similar to "Escape Room". Someone found a photo of Pineapple Cake in the street view, and the English name of this dessert happened to be the beginning of P. So some people speculated that the code of Android 9.0 system is likely to be pineapple cake, but this speculation was denied.
In February 2018, the initial codename for Android 9.0 was designated Pistachio Ice Cream, which was temporarily translated into pistachio ice cream and exposed some features. 
In September or October 2018, GooglePixel is expected to release the pre-installed Android 9.0 system that will be released at that time.
Android 9.0 HDR VP9 video, HEIF image compression and Media API
Android 9 adds built-in support for High Dynamic Range (HDR) VP9 Profile 2, so you can now offer users HDR-capable movies from YouTube, Play Movies, and other sources on HDR-enabled devices.
Android 9 adds support for HEIF (heic) image encoding for the platform. Examples of HEIF still images supported in the MediaMuxer and MediaExtractor classes HEIF improves compression, saving storage space and network data traffic. Sending and using HEIF images from back-end servers is a breeze with platform support on Android 9 devices. After ensuring that the app is compatible with this data format that is easy to share and display, try using HEIF as the image storage format in your app. You can use ImageDecoder or BitmapFactory to convert jpeg to heicto to get bitmaps via jpeg, and you can use HeifWriter to write HEIF still images from YUV byte buffers, Surfaces or Bitmaps.
Media metrics are also available through the AudioTrack, AudioRecord, and MediaDrm classes.
Android 9 adds functions to the MediaDRM class to get metrics, high-bandwidth digital content protection (HDCP) levels, security levels, and sessions, with more control over security levels and security stops. For more details, please refer to the API Differences Report.
In Android 9, the AAudio API includes the AAudioStream property for usage, content type, and input preset. Use these properties to create a stream that is adjusted for VoIP or camera applications. You can also set the SessionID to associate the AAudio stream with a submix that can contain sound effects. Use the AudioEffect API to control the sound.
Android 9 includes an AudioEffect API for DynamicsProcessing. With this class, you can build channel-based sound effects that consist of multiple stages of various types, including equalization, multi-band compression, and limiters. The number of frequency bands and active phases is configurable and most parameters can be controlled in real time.