How to Fix Audio Delay on an MP4 Video

By Scott Shpak

Updated September 22, 2017

Synchronization errors as low as 25 milliseconds can be detected by viewers.
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There's a peculiar charm to vintage monster movies with poorly dubbed, out-of-sync voice overs, but generally video that's ahead or behind the audio distracts from your viewing experience. Occasionally, audio delay results from a computer problem, but when the error appears in the MP4 video itself, using software to move the sound ahead or back in relation to the video may not save Tokyo, but it will restore proper synchronization.

The MP4 File Format

The MP4 file format is a standard whose full designation is MPEG-4 Part 14. MP4 addresses the coding of audio-visual objects, in particular how the images within an MP4 file are compressed, so that the file takes up as little space as possible to facilitate transfer or broadcast over the Internet. Unlike film, where the sounds are printed beside the images in a copy of a film, video and audio information are separate components of the MP4 file.

Rule Out Your Computer

When delays in audio become noticeable, consider the underlying cause before attempting to alter the MP4 file. Check another file to see if the audio delay is similar. If several files show delay when you previously had no problem, rebooting your computer may free up system resources, such as memory and disk caching, allowing your video player to work efficiently. Adding or changing media players may also affect audio delays in several files, as may incorrect media player settings. When your audio delay affects only one file, your computer is likely not the culprit.

Address the File

Video and audio compression usually work well together, maintaining alignment as a video is encoded. Sometimes, however, the compression of each component is at a slightly different percentage, and the resulting time difference becomes noticeable. Occasionally, when files are copied and shared, data within the file may become corrupted, leading to sync problems. Other times, sync errors can be introduced by the editor when the file is compiled and not fixed before encoding.

Making the Time Shift

Your media player may be capable of correcting audio delay. Products such as VLC, KMPlayer and MPlayer incorporate audio shift controls. VLC, for example, shifts the audio forward and backward in 50 millisecond increments using the J and K keys. These adjustments are effective, but temporary. Repairing a file with audio delay requires a utility to correct code corruptions and synchronization problems. Programs such as WinAVI, Avidemux and Yodot MOV Repair provide this correction, though be sure to work on a copy of any file you can't replace.