Netflix said it was responding to customer demand. But the trial has provoked an angry backlash from Hollywood film-makers including Judd Apatow, Peter Ramsey, Peyton Reed and Brad Bird.
Some Netflix subscribers said they approved of the idea, as the speeded-up function would allow them to skip the "boring" parts and the slower speed would help those who struggle with hearing.
The speeds - 0.5x, 0.75x, 1.25x or 1.5x - are being trialled on Android devices. Netflix said the service automatically corrects the pitch, meaning speeded-up dialogue does not result in squeaky voices.
Responding to the backlash, Netflix's vice president of product, Keela Robison [CORR], acknowledged that the test "has generated a fair amount of feedback - both for and against".
She said: "We regularly test new features that could help improve Netflix. In the last month, we've started testing several additional player controls, including… the speed at which you watch on mobile.
"It's a feature that has long been available on DVD players - and has been frequently requested by our members. For example, people looking to rewatch their favourite scene or wanting to go slower because it's a foreign language title.
"We've been sensitive to creator concerns and haven't included bigger screens, in particular TVs, in this test. We've also automatically corrected the pitch in the audio at faster and slower speeds.
"In addition, members must choose to vary the speed each time they watch something new - versus Netflix maintaining their settings based on their last choice.
"We have no plans to roll any of these tests out in the short term. And whether we introduce these features for everyone at some point will depend on the feedback we receive."
