/System/Library/Frameworks/VideoToolbox.framework/Versions/A/XPCServices/VTDecoderXPCService.xpc/Contents/MacOS/VTDecoderXPCService VTDecoderXPCService process is a sanboxed host used by QuickTime for video and audio decoding. Whenever an application is using the os-built-in audio and video API, VTDecoderXPCService will start and will be doing the parsing of the content.
The binary is a part of VideoToolbox public framework.