The main implementation is here: https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/cmds/bootanimation, different product could have different bootanimation.zip prepared, which would be copied to the /system/media/bootanimation.zip path.

FORMAT.md

defines how to organize the contents of the bootanimation.zip file

BootAnimation.cpp

BootAnimationUtil.cpp

• bootAnimationDisabled

  checked the property of debug.sf.nobootanimation, ro.boot.quiescent, ro.bootanim.quiescent

• waitForSurfaceFlinger

  loop to wait for the SurfaceFlinger service

• playSoundsAllowed

  checks the properties of sys.boot_completed, sys.powerctl, persist.sys.bootanim.play_sound and ro.boot.bootreason

bootanim.rc

  service bootanim /system/bin/bootanimation
      class core animation
      user graphics
      group graphics audio
      disabled
      oneshot
      ioprio rt 0
      task_profiles MaxPerformance