What does Fix Audio Sync in Video do?
Fix Audio Sync in Video shifts the soundtrack relative to the picture. A positive offset delays the audio and can leave silence at the start. A negative offset advances the audio by skipping the start of the soundtrack. Video frame timing is copied when the stream can be copied. The file needs an audio track.
How to use Fix Audio Sync in Video
- 1Upload a video and read its duration.
- 2Choose a preset or enter an offset in milliseconds.
- 3Preview the offset when the browser can decode the audio.
- 4Export the MP4 and download it. Cancel stops the local job.
Supported inputs and outputs
Inputs
Local video with an audio track
Outputs
MP4 with the audio offset applied
Practical uses
- Correcting a small lip-sync error
- Delaying a soundtrack that arrives early
- Advancing a soundtrack that arrives late
Browser and media limitations
- A file with no audio track cannot be shifted.
- A positive offset can make the file longer than the video and leaves opening silence.
- A negative offset removes the start of the audio and cannot be larger than the soundtrack.
- Video is copied only when the source stream fits the MP4. Some codecs have to be rejected by the copy step.
- The audio is re-encoded. The media engine downloads on first export.
How local processing works
Your media is processed in this browser tab, not uploaded to a processing server. The media engine downloads on first export. Page navigation and analytics still use network requests. Download the result before closing the tab.
Frequently asked questions
Does a positive offset delay the audio?
Yes. Positive milliseconds play the sound later. The beginning can be silent.
Does this change the video frames?
No. The video stream is copied when the container can store it. Only the audio timing changes.
What if the video has no audio?
There is nothing to shift. The export needs an audio track.
Is the video uploaded?
No. Preview and export stay in this browser tab.