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Replace video audio

Pair a video with a new recording or soundtrack. Use Replace video audio locally with practical instructions, output settings and format limits.

A practical guide

Replace video audio

Replace a video’s existing sound with a separate audio recording and save a new encoded clip. Upload the video first and the audio second, then select the shared start and length. The replacement is trimmed or padded with silence to fit the selected video duration rather than mixed with the old track.

  • Add narration to a silent demonstration
  • Replace unwanted room sound with music
  • Pair a short visual clip with a separate recording

How to use Replace video audio

  1. Add video followed by audio

    Upload exactly two files with the video first and replacement audio second. The first must contain video and the second must contain a readable audio track.

  2. Set the shared time selection

    Enter start and length for the output, remembering that the audio trim also uses those values. Use prepared excerpts when the sources need different starting positions.

  3. Choose video output settings

    Select format, maximum width and quality, then run the replacement. The source video’s audio is replaced, with silence added if the selected replacement sound ends early.

  4. Listen for synchronization

    Download and play the result from beginning to end. Check narration timing, the start position and any silent tail before using the newly paired video and audio.

Understand the settings

Output format
Choose output format according to the result you need. Available choices: MP4; WEBM; MOV; MKV. The initial selection is MP4.
Maximum width
Maximum width accepts values from 16 to 1920, using whole numbers. The initial value is 1280. Change it for a specific output requirement, then check the result before processing more files.
Quality (lower = better)
Quality (lower = better) accepts values from 16 to 45, using whole numbers. The initial value is 26. Change it for a specific output requirement, then check the result before processing more files.
Start (seconds)
Start (seconds) accepts values from 0 to 7200, in increments of 0.1. The initial value is 0. Change it for a specific output requirement, then check the result before processing more files.
Length (seconds)
Length (seconds) accepts values from 0.1 to 120, in increments of 0.1. The initial value is 20. Change it for a specific output requirement, then check the result before processing more files.

Narration for a silent walkthrough

A twenty-second silent walkthrough needs a separate narration. Prepare the audio so its speech starts at the beginning, upload video first and audio second, and use start zero. Create MP4 and check that each instruction matches the visible action.

Check your result

Add exactly two files: video first, then audio. New audio is trimmed or padded with silence to the video duration. Media jobs are bounded to 120 seconds; animations to 240 frames, 30 seconds and 64 million decoded pixels. Open the saved output in the app or workflow where you plan to use it. Check one representative result before repeating the same settings with more files. The original files stay unchanged.

What to know before you start

  • Files are processed on this device. Browser memory and engine-specific limits apply. Save results before reloading.
  • Media jobs are bounded to 120 seconds; animations to 240 frames, 30 seconds and 64 million decoded pixels.
  • Upload up to 20 files, at least 2 with a combined size of at most 100 MB. The completed output must fit within 200 MB.
  • Files are checked by the local engine; a matching filename alone is not proof of valid contents.
  • Selections and completed jobs stay available while you navigate inside this tab. Use My files to revisit results. Reloading or closing the tab clears the workspace; download results you want to keep first.

Replace video audio: common questions

Does replacement mix both soundtracks?

No. The result uses the selected audio from the second file in place of the video’s original track. It does not expose volume mixing between old and new sound, so prepare a combined soundtrack separately if needed.

What if the replacement audio is too short?

The selected replacement is padded with silence to cover the video duration when needed. This avoids shortening the visual clip, but it can leave an unintended silent ending, so listen through the complete downloaded result.

Can video and audio use different start values?

There is one shared start setting in this tool. It applies to the video selection and the replacement audio trimming, so prepare separately trimmed source copies when narration should begin at a different source timestamp.

Can I upload more than two files?

This operation requires exactly two files in role order: video first and replacement audio second. Join or edit multiple audio recordings into one prepared soundtrack before using it as the replacement input here.

Does Replace video audio upload files to another service?

Processing runs in this browser, on your device. Files and pasted input are not uploaded to a conversion server. The website and required engine assets must load first; large operations depend on available device memory.

Can I continue after changing pages?

Selections and completed jobs stay available while you navigate inside this tab. Use My files to revisit results. Reloading or closing the tab clears the workspace; download results you want to keep first.