HandBrake is very CPU intensive. It supports hardware accelerated encoding, which is only for video encoding, and is not used for video decoding, filters, audio encoding, muxing and audio/video sync. So the CPU usage of HandBrake is usually high (even as high as 99%). Here's how you can enable GPU acceleration on HandBrake: Go to the menu bar > select Tools > Preferences > Video > see the supported and available hardware encoder.