So what's in the secret sauce? e.g. faster-whisper "is a reimplementation of OpenAI's Whisper model using CTranslate2" and claims 4x the speed of whisper; what

So what's in the secret sauce? e.g. faster-whisper "is a reimplementation of OpenAI's Whisper model using CTranslate2" and claims 4x the speed of whisper; what does insanely-fast-whisper do to achieve its gains?