I was about to port 2.3 of the original content to 4.0 recently, but it was difficult at the beginning: I couldn't find the definition of the variable. This seems to be a bit embarrassing. After so long, Android cannot find the corresponding header file. However, it was soon discovered that the content of the following paths had greatly changed in 4.0.
/System/CORE/include/System
/System/Media
/Hardware/libhardware
/Hardware/libhardware_legacy
Especially for/system/CORE/include/system/audio. H, the Audio-related concepts originally defined in audiosystem. h are now moved to this file. I do not understand the truth for the moment. In theory, the content in/system/core is prepared for the minimum system. What is the relationship between audio and audio?
Similarly, some definitions in audiopolicymanagerbase. h are also moved to/system/CORE/include/system/audio_policy.h.
Some header file positions related to sound effects have also changed.
Android4.0 makes some adjustments to the Hal layer to make Hal and framework more independent from each other. This may be the reason why audio-related definitions are removed from the framework.