The Windows Media MMR (multimedia redirection) feature, for Windows 7 and Windows 8/8.1 desktops and clients, enables full-fidelity playback on Windows client computers when multimedia files are streamed to a remote desktop.
With MMR, the multimedia stream is processed, that is, decoded, on the Windows client system. The client system plays the media content, thereby offloading the demand on the ESXi host. Media formats that are supported on Windows Media Player are supported; for example: M4V; MOV; MP4; WMP; MPEG-4 Part 2; WMV 7, 8, and 9; WMA; AVI; ACE; MP3; WAV.
You must add the MMR port as an exception to your firewall software. The default port for MMR is 9427.