(Reuters) - Shares of speech-recognition software maker Nuance Communications Inc touched a 2-1/2-year high on Tuesday, after a website posted a video of Apple Inc co-founder Steve Wozniak saying the iPhone maker had bought Nuance.

The stock rose as much as 12 percent to $19.19, but later pared some gains to trade up 5 percent at $18. More than 9 million shares changed hands by 1 p.m. ET -- five times the normal volume.

A video clip posted on TVDeck.com showed Wozniak as saying, "They (Apple) recently bought the company Nuance that does a lot of great voice recognition."

Nuance said it doesn't comment on speculation, while Apple declined to respond.

Deutsche Bank analyst Nandan Amladi attributed the rally in Nuance shares to the speculation, but said an acquisition was unlikely.

"Nuance licenses its technology to many vendors including competitors to Apple. By acquiring Nuance, its value goes down because its competitors would stop licensing Nuance," he said.

On Monday, Burlington, Massachusetts-based Nuance posted better-than-expected fourth-quarter results, helped by strong revenue at its healthcare and mobile units.

Nuance forecast 2011 revenue above expectations and earnings largely in line.

Avondale Partners said the full-year outlook reflects the current trend of strong demand for the company's products, its mobile design wins and growing acceptance for its mobile technologies.

Gleacher & Co reiterated its "buy" rating on the stock, citing its diversified end-markets, dominant market share position and increasing revenue visibility.

(Reporting by Sayantani Ghosh in Bangalore and Sinead Carew in New York; Editing by Vinu Pilakkott)