Add Audio to Video Tool

Merge, replace, or mix audio tracks with a video. Fast when it can be.

Advertisement

Video Preview

Audio Track

Audio Settings

📹 Full video kept - stays at 00:00.000. Audio added starting at 00:00.000 for 00:00.000.

New audio replaces the original video sound

Adjust loudness (100% = original)

Universal compatibility

Better quality

Stream copy for speed (limits some effects)

💡 Quick Guide

  • Step 1: Upload your video and audio files
  • Step 2: Set video time range (where audio will play)
  • Step 3: Set audio time range (which part to use)
  • Step 4: Full video kept, audio added at the selected position
  • Tip: If audio is longer than video, it auto-trims to fit
  • Fast mode: roughly 10x quicker with stream copy enabled
  • Mix mode: combines both audio tracks (takes longer)

Why People Use PixDuplicate's Audio Merger

Replace or Mix

Swap the original soundtrack entirely, or layer new audio on top of it. Voiceover over ambient sound, music under narration—whatever the project calls for.

Fast When It Can Be

For simple audio replacement without effects, stream copy skips re-encoding. A 30-minute video can finish in seconds.

Volume and Fades

Control how loud the new audio sits, and add fade-in and fade-out so it doesn't just start and stop abruptly.

Nothing Gets Uploaded

Everything runs in your browser. Your video and audio files never leave your device—no servers, no cloud.

Pick Your Mode

Replace kills the original audio. Mix keeps both. The tool tells you which one is faster before you commit.

Common Formats In, Common Formats Out

Input: MP4, WebM, MOV, AVI video. MP3, WAV, AAC, OGG, M4A audio. Output: MP4, WebM, or MOV.

How the Audio Merger Works

Putting new audio on a video—without sending either anywhere

Step 1: Add your files

Drop in a video and an audio file. Supports MP4, WebM, MOV, and AVI video up to 2GB, and MP3, WAV, AAC, OGG, M4A audio up to 500MB.

Try the example files first if you just want to see how the timing controls work before uploading your own.

Step 2: Set the timing

Choose where the audio sits:

Video range: pick the exact start and end point in the video where the audio should play

Volume: anywhere from 0% to 200% of the original level

Mode: replace the original audio entirely, or mix the new track with it

Fades: add a fade-in and fade-out so the audio slides in and out instead of cutting hard

Step 3: Pick the processing method

Two ways the tool can handle it:

Stream copy: skips re-encoding, handles compatible files in seconds, but only works for simple replacements

Full encode: slower but supports mixing, volume changes, and fades

Quality: pick the output quality if you're re-encoding

Output format: MP4, WebM, or MOV

Step 4: Process and download

Once it's done:

Preview the merged video with the new audio playing

Download the file with a sensible filename

See which processing method got used and how long it took

Go back and tweak the settings if the first pass isn't right

Tip: If you're just replacing audio with no effects and no mixing, leave stream copy on. That's the mode that turns a half-hour video into a few seconds of processing.

Your Files Stay on Your Device

Unlike other online video tools, PixDuplicate does all the work locally in your browser. That means:

Your video and audio never leave your device
No uploads, no cloud processing
No sign-up or personal info needed
Completely free with no limits
No watermarks on your merged videos
Works offline after the page loads

What Users Are Saying

Podcasters, editors, and creators use PixDuplicate to sort out their audio

4.9

Based on 402 reviews

Devin Holloway

"I record podcast audio separately from the video for better quality, then use this to stitch them back together. Stream copy mode takes seconds even on long episodes. The only thing I'd add is a preview waveform so I can visually confirm the sync, but the audio preview does the job."

6/19/2025

Priya Ramakrishnan

"I do product demo videos for a SaaS company. Voiceover goes on top of a muted screen recording, and this handles that perfectly. The fade controls make the transitions sound intentional instead of jarring. No uploads matters too—the demos aren't public yet."

2/27/2026

Wyatt Beckwith

"Works well but I've hit the limit on what stream copy can handle a couple of times—it won't mix tracks or apply fades, which is fine, but the tool should make that clearer up front. Once I figured out that replacing audio = fast and mixing = slow, everything made sense. Solid otherwise."

10/14/2024

Nadine Aguilar

"I shoot wildlife clips and often the camera audio is unusable—wind noise, my own breathing, whatever. Strip the original, layer in a natural soundscape track, done. Faster than opening Final Cut for the same task."

4/8/2027

Callum Everett

"The precise start time controls are what sold me. I do video editing for a law firm and need to sync deposition audio to the exact second. Setting the video start to, say, 00:03:24 is trivial here. Would be 5 stars if it also supported stereo panning for the mix mode."

1/5/2025

Halima Osei

"Used this to add background music to a wedding video the couple had already approved without it. Mixed instead of replaced so you can still hear the vows underneath. Volume slider let me drop the music to about 15%—just enough to notice, not enough to drown anything out."

8/22/2024

Common Questions

What formats can I use?

Video input: MP4, WebM, MOV, AVI. Audio input: MP3, WAV, AAC, OGG, M4A. Output: MP4, WebM, or MOV. MP4 is the safe pick if you're not sure what you need.

What's the difference between stream copy and full encoding?

Stream copy skips re-encoding and just swaps the audio track, so it's very fast—sometimes seconds for a long video. But it only works when you're replacing audio, not mixing, and no effects are applied. Full encoding is slower but handles mixing, volume changes, and fades.

Can I mix instead of replacing?

Yes. If the source video has audio, you can either replace it entirely or mix the new track with it. Mixing is how you'd layer background music under narration that's already in the video. It requires full encoding, so it takes longer than stream copy.

Is there a file size or length limit?

Video up to 2GB, audio up to 500MB. No hard limit on length, but very long videos take longer to process—especially in full encoding mode.

Are my files private?

Yes. Everything runs locally in your browser using WebAssembly. Your files never get uploaded anywhere. That matters when the video isn't public yet.

Why would I need this?

Voiceover for a tutorial, music under a montage, replacing bad camera audio with clean recorded sound, dropping a soundtrack on a video that was shot silent, or fixing the audio sync on a clip where the sound and picture drifted.

Does it hurt video quality?

Stream copy doesn't touch the video stream at all—quality stays identical. Full encoding re-encodes, but the quality settings let you dial in how much to compress. At High or Lossless, the difference is negligible.

Can I adjust volume and add fades?

Yes. Volume goes from 0% up to 200% of the original level. Fade-in and fade-out have custom durations so the audio doesn't just start and stop abruptly.

What if the audio is longer or shorter than the video?

You control the timing with the start and end sliders. If the audio is longer than the video range you selected, it auto-trims to fit. If it's shorter, it just ends early and the rest of the video plays with the original or silent audio.

Can I use this for commercial work?

Yes. Personal and commercial both fine. No watermarks, no attribution, no licensing restrictions.

Discord logo

Need Assistance? Join Our Discord!

If you're unsure how our website works or need help finding duplicate images or using our image compression tool, or have any suggestions for improvement, don't hesitate to join our Discord server.
Product Hunt logo

Share Your Feedback on Product Hunt!

If you have any suggestions for improving our website, or if you'd like to let us know what you think about our features, feel free to leave your feedback on Product Hunt. Your input helps us grow and serve you better!