Bluetooth audio latency

Bluetooth headphones receive compressed audio over a radio link that can drop out for a moment, so they buffer it before playing. Encoding with the link's codec, sending, buffering and decoding together add a delay you can hear in games and calls. Video players hide it by holding the picture back to match; a game or a call is live and cannot.

A browser cannot read most of it. Browsers report an output latency for the audio path, but that figure describes the system's side and rarely includes the buffering inside the headphones, and the browser is not told which codec the link negotiated. The Bluetooth latency test measures what you hear instead: it plays clicks on the audio clock, you tap along, the first 2 are dropped while your rhythm settles, and the median gap is the delay. Run it once on the headphones and once wired; the difference is the link's share.

Our warn line is 120 ms, set at the detectability threshold ITU-R BT.1359 gives for sound arriving after the picture; past 250 ms, our own line, sound is plainly behind. A low-latency or game mode, a low-latency codec both ends support, a headset with its own 2.4 GHz dongle, or a cable each bring it down.