Audio and video sync test. Slide until they line up.
A flash and a beep start together once a second. Through wired speakers they line up; through Bluetooth headphones the beep arrives late. Move the slider until the beep lands on the flash, and the offset is how late your sound runs.
One check
- Audio and video sync
One check after another, with your progress along the top and a plain verdict on each. Nothing you show the camera or say into the microphone leaves this page.
What it measures
Measured here, not assumed.
- The pair
- The beep is scheduled on the audio clock; the flash is drawn on the page clock at the same instant, held back by the slider's offset. The flash is a soft fade, never a strobe; with reduced motion switched on it is dimmer and fades more slowly.
- The offset
- Positive means the sound arrives after the picture, the Bluetooth case. The range runs from 200 ms early to 500 ms late in 5 ms steps.
- Against what people notice
- The same lines as the audio latency test: our warn line of 120 ms sits at the point ITU-R BT.1359 gives for late sound becoming detectable; past 250 ms, our own line, it is plainly behind.
If it fails
The usual failures, and what fixes each.
- Bluetooth runs 150 to 300 ms late
- That is normal for the standard Bluetooth codecs, SBC and AAC, which buffer audio to survive radio dropouts. aptX Low Latency and LE Audio's LC3 cut it a long way where both the computer and the headphones support them. A cable removes it.
- A TV or soundbar is in the path
- Switch on its game or low-latency mode, and turn off picture and sound processing. A TV's picture processing can also make sound seem early.
Where a browser stops
What it cannot tell you.
- Your own judgement of when two things line up, which is good to a few tens of milliseconds.
- Which part adds the delay: the Bluetooth codec, the headphones or the system. It is the total you see and hear.
- Delay in a specific app. Video players hold the picture back to match; games and calls cannot.
Privacy
Nothing leaves this page.
The camera and microphone are read on this page and stopped as soon as they have been measured. The clip you can play back lives in the browser's memory and is discarded when you leave. The location check discards the position. The internet test sends random bytes to this site and nothing else. The result is stored nowhere unless you ask for it by email, and then only the fact that an email was sent is kept.
Questions
Audio and video sync test, answered
- Why is Bluetooth audio out of sync?
- Bluetooth audio is compressed by a codec and buffered so a moment of radio interference does not cut out the sound. The standard codecs, SBC and AAC, usually add 150 to 300 ms. Low-latency codecs add far less where both ends support them.
- How do I measure audio delay on my headphones?
- Connect them, run the test above, and move the slider until the beep lands on the flash. The offset is the delay. The audio latency test measures it a second way, by tapping along to clicks.
- Is the flash safe for people sensitive to flashing?
- It is one soft fade a second, never a hard on and off, well under the three flashes a second that WCAG 2.3.1 sets as the limit. With reduced motion switched on, it is dimmer and slower again.
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