One of the world's leading pianists has surprised concertgoers by storming off stage because a fan was filming his performance on a smartphone.
Krystian Zimerman, 56, returned moments later and declared: "The destruction of music because of YouTube is enormous."
He carried on with his recital, but chose not to perform an encore and cancelled a post-concert reception.
The Polish pianist joins several high-profile musicians who have spoken out against filming.
In April, indie rock band the Yeah Yeah Yeahs put up a note for fans entering a gig.
"Please do not watch the show through a screen on your smart device/camera," it said, along with some stronger words.
Former Pink Floyd bassist and vocalist Roger Waters described filming at gigs as showing a "lack of respect" to the artist.
Zimerman was performing at the Ruhr Piano Festival in Essen, western Germany, where he was said to have spotted a member of the audience filming the concert from the balcony.
"He noticed someone up in the choir seats filming the concert on their smartphone. We think it was probably an iPhone," said festival spokeswoman Anke Demirsoy after the performance.
"He asked them to stop, but they didn't. So he interrupted the recital and walked off stage."
Zimerman then apparently told the audience that he had lost recording contracts and projects because of recording company executives telling him: "We're sorry, that has already been on YouTube."
The festival's director, Franz Xaver Ohnesorg, said he sympathised with Zimerman's frustration.
He told German media: "What happened is theft, pure and simple. It cuts particularly deeply when the artist is of a sensitive nature."
The BBC could not reach Zimerman on Wednesday for comment.
Jasper Hope, chief operating officer at London's Royal Albert Hall, said filming at live events was not a problem - as long as it did not disturb the artist or the audience.
"It's not hard to be discreet," he told the BBC.
"If you're the kind of artist that is prepared to use digital media to promote yourself, then provided you're not distracted I don't see a problem with that."
He added: "Do I seriously think that recording contracts for any artists can be jeopardised in this way? No I do not. It is becoming part and parcel of modern music promotion."
Violinist and composer Steve Bingham said for many musicians the issue was not about theft, but instead about terrible quality.
"You want people to pass on your music to friends, but the downside is you don't get the quality control you want if someone is recording in the 17th row on a smartphone.
"You either miss the bass because phones don't pick up the bass or the view is such that visually it isn't that good."
Frustration at amateur filming is not just shared among musicians.
British comedian Lee Hurst found himself in court in 2009 after smashing up an audience member's mobile phone during a gig.
He told the court: "TV programmes have writers writing for the performers and they go around to gigs and take the material and sell it to the BBC and ITV and that material is gone.
"You are then accused of stealing your own material. It has happened to me with material shown on national TV that I had already done.
"There are thieves amongst the circuit, sadly, and amongst the writing community.
"Nobody will protect us, we have to protect ourselves."
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