Audio out of sync in 4K videos

[lyly19]

When I play 4K videos (MP4, H.265) on a Windows 10 PC using VLC and MPC-HC, the audio gradually becomes out of sync with the video by about 0.5–1 second after a few minutes, even though the same file plays fine on my phone. Is there a way to fix this audio delay issue without re-encoding the entire video?

[Nazrin544]

This usually happens due to hardware decoding or clock drift on the PC. Try disabling hardware acceleration in VLC/MPC-HC and make sure your GPU drivers are up to date. Also check the audio output settings (set them to default/DirectSound). These fixes often stop the gradual audio desync without re-encoding the video.

[MrDoom3412]

It happens due to decoding or sync issues, so first try enabling hardware acceleration in VLC/MPC-HC and update your GPU/audio drivers, as that alone often fixes drift. You can also switch the audio output module like DirectSound <> WASAPI or disable “time stretching”/audio sync options in the player settings. If it still drifts, manually apply a small audio delay in the player or remux the file using a tool like MKVToolNix to correct timing.

[mellatyadak]

The audio-video desynchronization you are experiencing is likely caused by your PC’s hardware struggling to keep up with the intense processing requirements of 4K H.265 (HEVC) decoding, rather than an issue with the file itself. To fix this without re-encoding, first ensure that hardware acceleration is enabled in your media player: in VLC, go to Tools > Preferences > Input/Codecs and ensure “Hardware-accelerated decoding” is set to “Automatic” or “Direct3D11,” which shifts the workload from your CPU to your GPU. If the issue persists, consider switching to a more modern, lightweight player like MPV or PotPlayer, which generally handle 4K H.265 overhead much more efficiently than VLC. As a temporary manual fix during playback, you can use VLC’s synchronization hotkeys—press ‘J’ (to delay audio) or ‘K’ (to speed up audio) in 50ms increments—to realign the tracks on the fly without needing to modify the file structure.