I wish to install a set of new sirens into the game, normally it can be done by just importing the 'vehicle.oac' file into the ' x64/audio/../../' folder. The thing is, the modder did not provide a vehicle.oac in the siren files, what he provided were just a string of wav files zipped into a sigle 'siren.rar'. So obviously one needs to reconvert all these wav files into the original vehicle.oac or awc file? I've been looking everywhere trying to find a solution but no luck has turned up.

Create a new folder on your desktop. You can name it anything. Select vehicles.awc in openIV, right-click and select "Output with openFormats" and then select the folder you just created. A vehicles folder and vehicles.oac will be created in the folder, so after replacing the wav in the vehicles folder, drag and drop oac into the location of vehicles.awc to convert it to awc.

I'm sorry if this is difficult to understand because I'm using a translation.

Your topic has been moved to GTA V Support, this is not LSPDFR related.
Please post in the correct location in the future.