If you're using Facebook on your mobile device - as 874 million users do every month - then watch out that its new video element doesn't push you over your data allowance.
The new element in Facebook's News Feed will show video ads and videos posted by your friends in the content that you're shown.
But those posted by your friends might take up some of your data allowance if you watch them when not connected to Wi-Fi.
The ads won't be downloaded on mobile - "for now", says Facebook; they'll be downloaded while you're on Wi-Fi. (It's not clear how long "for now" will last.)
But other videos that people have posted to your News Feed will download wherever you are unless you block them in your settings.
"You can allow some of these videos to play automatically over Wi-Fi only", the company says in its note about the video element. Again, it's unclear how many "some" is in this context. But if you don't want to get a surprise when your next phone bill comes in, it might be a good idea to disable video downloads over mobile data.
Facebook began introducing users' video into News Feeds in September, but didn't offer any details about whether its download would happen over Wi-Fi or mobile.
On 17 December, though, it said that it was offering marketers "a new way to tell stories in News Feed"- in other words, introduce video ads. In the blogpost about that, it said that
"On mobile devices, all videos that begin playing as they appear on the screen will have been downloaded in advance when the device was connected to WiFi — meaning this content will not consume data plans, even if you’re not connected to WiFi at the time of playback".
But the wording of the warning to users seems to imply that that won't always be the case.
What if you don't use the app, but view Facebook on the web? That's unclear too - though you might need to check settings on your phone there too.
We'll try to clarify the details with Facebook over quite what "for now" means about video ads and what "some" refers to in allowing videos to play on Wi-Fi.
Below are the pictures (courtesy of James Whatley) showing how to turn off mobile data use on iOS and Android.
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