Unity3D Audio Grabber design
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This document discusses the design of a Unity3D Audio Grabber tool that records audio from Unity3D games. It explains that the tool will link with the FMOD Ex library and hook certain FMOD functions, like FMOD_System_Create, to get the FMOD system object and manipulate FMOD audio. It will then take the audio buffer data and encode it along with video into an .MP4 file using MediaCodec. The tool is designed to work similarly to how another tool called libkamcordaudio grabs audio in Unity3D games.
Unity3D Audio Grabber design
- 1. Unity3D Audio Grabber design Unity3D is tested on version 4.6 Jungsoo Nam namjungsoo@gmail.com 2015/03/17
- 2. FMOD Ex • Libunity.so uses FMOD Ex statically(with .c sources or .a archive) linked. • NOT uses libfmodex.so • NOT will be applied by function hooking with Elf32_Ehdr like eglSwapBuffers()’s method. • C++ based library, but C wrapper classes. • C functions can be hooked.
- 3. IDA analysis – libunity.so • ONLY Imports tab’s functions can be hooked. FMOD’s are in Exports tab. (Function pointers are NOT in imports entry table.)
- 4. FMOD hooking • FMOD C API hooking is essential.(libkamcordaudio.so does like this) • Getting/sharing FMOD system object is important for interoperating AudioGrabber with Unity3D FMOD audio. • So we have to hook FMOD_System_Create(FMOD_SYSTEM** system) • How to hook FMOD? • Find another entry table.(exports table) • In VideoGrabber, we found imports table.(libunity.so imports libGLES*.so function) • Next we have to find exports table.(libunity.so exports some functions to client) • Or use “dlsym()” again. • orig_FMOD_System_Create = dlsym(RTLD_DEFAULT, "FMOD_System_Create"); • LOGD("FMOD_System_Create: 0x%x", orig_FMOD_System_Create);
- 5. Final AudioGrabber design • AudioGrabber will be like below: • Link libfmodex.so. • Hook some FMOD functions and get FMOD system object. • Use our FMOD functions in libfmodex.so, manipulate FMOD audio and get audio buffer data. • Put audio buffer data into MediaCodec. • Mix and encode video and audio to .MP4
- 6. Thank you