Smart TVs screenshot what you watch several times a second – even over HDMI

01 Nov 2024 | Rasmus Larsen |

All Smart TVs use ACR technology to take screenshots of what you watch multiple times per second, even when using HDMI, a new study concludes. The study focused on LG and Samsung's use of ACR (Automatic Content Recognition) and while the method did not allow the authors to see exactly what is captured, they were able to analyze the traffic between the TV and server to determine how often and how much data is collected on your TV.

How ACR works. Illustration: Study

- "While prior research has investigated third-party tracking in the smart TV ecosystem, it has not looked into second-party ACR tracking that is directly conducted by the smart TV platform," wrote the researchers behind the 'Watching TV with the Second-Party' report. One finding is that Smart TVs constantly send large amounts of data about what you watch to the servers. LG captures a screenshot of your TV every 10ms (100 times per second), while Samsung does so every 500ms (twice per second). However, Samsung "transmits up to 2X more data at a higher frequency to ACR domains as compared to LG" when using the TV's app platform.

Even when using HDMI

ACR tracks your viewing activity even when your TV is connected to an HDMI device such as a media player or PC, which "raises privacy concerns", according to the authors. In other words, your TV can snoop on content like family photos or sensitive data. - "When a user connects their laptop via HDMI just to browse stuff on their laptop on a bigger screen by using the TV as a ‘dumb’ display, they are unsuspecting of their activity being screenshotted," one of the researchers, Yash Vekaria from University of California, Davis, told New Scientist. In fact, the study found that much more data is typically collected via ACR when the TV is used with HDMI or for linear broadcasting (channels), and here LG is not the bigger data collector. Netflix and YouTube appear to have agreements in place to prevent LG and Samsung from collecting ACR data. - "ACR network traffic is not present when streaming content from third-party apps such as Netflix and YouTube," the study found.

Disconnect your Smart TV

While the study concludes that "the opt-out mechanisms implemented on LG and Samsung smart TVs are working", it is "typically not straightforward, often requiring navigation through various settings in multiple subsections, with no universal off switch", but instead up to 11 different menu options. A better solution is to disconnect your Smart TV from the internet entirely and use an external box such as the Apple TV 4K (review), which does not use ACR and has no ads on the homescreen. Smart TVs cannot utilize ACR when they are offline. - "As future work, we plan to explore more advanced man-in-the-middle (MITM) techniques to understand the payload of ACR network traffic. Moreover, we plan to investigate the link between ACR tracking and ad personalization in smart TVs," the authors said. Here is the frequency and amount of data transmitted by LG (left) and Samsung (right) Smart TVs when used in the UK, according to the study: