Ascent Media Group LLC said Monday that it has signed an agreement to sell its subtitling business, Visiontext, to SDI Media, a large subtitling and language dubbing provider for feature films and television shows.

This deal will mark the start of a long-term strategic relationship between the two companies, according to Santa Monica-based Ascent Media, which acquired United Kingdom-based Visiontext in 2000. Terms of the deal were not disclosed.

Visiontext also supplies subtitles for the deaf and hard of hearing for UK commercials. After the acquisition, Los Angeles-based SDI will continue to service Visiontext’s existing customers, the companies said.

Ascent Media Group is a wholly-owned subsidiary of Ascent Media Corp., which provides creative and technical services to the media and entertainment industries. SDI Media is owned by private equity firm Elevation Partners, whose partners include Bono, lead singer and co-founder of the rock band U2.