Instructions: Answer the question from the given passage. Your answer should be directly extracted from the passage, and it should be a single entity, name, or number, not a sentence.
Input: Passage: BSkyB's standard definition broadcasts are in DVB-compliant MPEG-2, with the Sky Movies and Sky Box Office channels including optional Dolby Digital soundtracks for recent films, although these are only accessible with a Sky+ box. Sky+ HD material is broadcast using MPEG-4 and most of the HD material uses the DVB-S2 standard. Interactive services and 7-day EPG use the proprietary OpenTV system, with set-top boxes including modems for a return path. Sky News, amongst other channels, provides a pseudo-video on demand interactive service by broadcasting looping video streams. Question: What is the proprietary system that Sky+HD uses?
Output:
OpenTV