(Android) Adding sound effects to your custom bootanimation
In this guide, I will be briefly introducing the concept of adding sounds to the bootanimation.zip structure found in every Android device. This means that you can use a custom substratum theme that comes with boot animation, on an AOSP based ROM or derivative.
There have been a line of OEMs that are known for their start up tones — Samsung’s swish, HTC’s piano, etc. Attached below is an example boot animation with sound from stock SM-G955N (Samsung Galaxy S8+ Korean variant) on SKT carrier.
Adding sound to a boot animation is rather simple, involving the addition a file named audio.wav to the folder of the individual parts of a boot animation to have it play when the part starts playing.
A typical bootanimation follows this structure:

To have a sound effect played as part4 is initialized, you just have to add an audio.wav to the part4 folder, so when part4’s frames begin to play, the sound file will be played as well!

It is common practice to have the boot animation play at the end or the start of the boot animation. It will be my recommendation to refrain from using any sound during the loops as loops inside the configuration file will keep restarting the part — hence the sound you thought you would only hear once, will keep looping (unless this is the intended behaviour!).
Now, let’s be creative and design amazing boot animations!
