Fixing Audio Delay
Why lips don't match words, and how to fix it.
1. The Bluetooth Latency Trap
If the audio is late by a consistent fraction of a second, the culprit is almost always Bluetooth headphones. Standard Bluetooth connections (SBC codec) have a latency of ~200ms. AptX Low Latency drops this to ~40ms, but both your headphones and your PC must support it.
The Fix: Unfortunately, web browsers do not offer a native audio-offset feature to compensate for Bluetooth delay like VLC does. You must test with wired headphones to confirm if Bluetooth is the issue.
2. Software Decoding Dropped Frames
If the video starts synced, but slowly drifts further apart the longer you watch, your CPU is failing to keep up with the video decoding, causing video frames to drop while the audio track continues playing at normal speed.
The Fix: You need Hardware Acceleration. A 4K HEVC file played purely on a weak laptop CPU will always desync. See our Hardware Acceleration Guide to ensure your GPU is handling the load.
3. Badly Muxed Files
If the audio is off by exactly the same amount from start to finish, the file was encoded (muxed) incorrectly by whoever created it. The audio track was simply shifted on the timeline before being exported.
The Fix: You can permanently fix the file using ffmpeg to shift the audio track without re-encoding.
Delay audio by 0.5 seconds:
ffmpeg -i input.mp4 -itsoffset 0.5 -i input.mp4 -map 0:v -map 1:a -c copy output.mp4