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Replace or mix a soundtrack · Independent gains · Picture stays lossless

Replace Video Audio

Replace or mix a soundtrack with exact gains, delayed start, duration planning, local preview, and lossless picture stream-copy.

This workflow reads the selected media from browser memory and creates the download locally. AntiUpload, analytics, and ads receive neither the file nor its working buffers.

No file uploadOn-device processingAds cannot access filesNo account
  1. 1Pick file
  2. 2Configure
  3. 3Download
The picture is never re-encoded. Pick the video here, then attach music, narration, or another audio track in the next step.
  • File contents and names never leave your browser
  • No upload server, cloud-processing copy or remote conversion queue
  • Free to use; capacity is limited only by your device and browser

About Replace Video Audio

Replace Video Audio keeps the complete file workflow inside this browser tab. Your selected file, its name, contents, settings, and generated output are not sent to AntiUpload or a cloud conversion service. Ads and aggregate traffic analytics stay outside the processing boundary and receive no file object or working buffer.

AntiUpload's Replace Video Audio tool swaps the soundtrack in a video or mixes a second track underneath the original. The video stream is copied byte for byte, so picture quality, frame rate, resolution, and compression stay untouched while only the audio is encoded.

Replace mode removes the original soundtrack. Mix mode keeps both tracks with independent -24 dB to +12 dB slider and exact-number controls, percentage feedback, and a peak limiter. Quick workflows set sensible voice-over, background-music, or looping-music balances without hiding the exact values.

Preview the replacement track, measure its duration, and place it at the start or capture a later start from the video player. A preflight plan compares both durations, predicts the output-length policy, and identifies the AAC or Opus audio route before local FFmpeg processing.

Three duration policies cover mismatched lengths: keep the full video and pad silence, loop the replacement to the video end, or stop at the shorter active track. MP4-family outputs use AAC, while WebM and Matroska use Opus for container compatibility.

How it works

  1. Pick the videoChoose MP4, MOV, WebM, MKV, AVI, M4V, or FLV. The video stream will be copied without re-encoding.
  2. Attach the new audioChoose music, narration, or another soundtrack in MP3, WAV, OGG, M4A, AAC, or FLAC format, then preview it locally and confirm its measured duration.
  3. Choose replace or mixReplace removes the old soundtrack. Mix keeps both and exposes independent gain controls with a limiter to reduce clipping.
  4. Place the track and choose a duration policyStart at zero or capture a later video time, then keep the full video with silence padding, loop short audio, or stop at the shorter active track. Review the predicted output duration and audio codec.
  5. Apply audioOnly audio is encoded. The picture is stream-copied into a compatible MP4, WebM, or MKV output.

When to use Replace Video Audio

Add background music beneath spoken video
Use Mix, lower the music track, and keep the original dialogue at a comfortable level.
Replace camera audio with a clean voice-over
Use Replace to discard room noise or scratch audio while preserving the original picture exactly.
Loop a short music bed across a longer clip
Choose Loop so a short licensed track repeats until the end of the video without manual duplication.
Start music after an intro or title card
Play the source preview to the exact entry point, capture that time, and leave the opening section untouched before the new track begins.
Localize a video with a translated narration track
Swap in the translated recording without waiting for a full video re-encode or uploading sensitive footage.

Frequently asked questions

Can I replace audio in a video without uploading it?
Yes. Both files stay in your browser and are processed on your device. No video or audio content is sent to AntiUpload servers. Input files are read from browser memory and the output is created locally for your download. AntiUpload does not send file bytes, names, sizes, page counts, contents, passwords, or generated outputs through analytics or advertising requests.
Does replacing audio reduce video quality?
No. The tool uses video stream-copy, so the encoded picture bytes are not changed. Only the selected audio output is encoded for the destination container.
Can I keep the original sound and add music?
Yes. Choose Mix both tracks, then lower the replacement gain so the original speech or environmental sound remains clear. A limiter reduces peaks when both tracks overlap.
What happens when the music is shorter than the video?
Choose Keep full video to pad the remaining soundtrack with silence, Loop to repeat the music until the video ends, or Shortest to end the output when either stream ends.
Can the replacement audio begin later than the video?
Yes. Enter an exact start time or capture the current source-preview position. FFmpeg inserts silence before the new track, while the selected duration policy still controls the output ending.
How do the gain controls work?
Each visible track can be adjusted from -24 dB to +12 dB with a slider or exact number. The percentage readout translates decibels into linear amplitude, and Mix mode applies a peak limiter after combining both tracks.
Which formats are supported?
Video inputs: MP4, MOV, WebM, MKV, AVI, M4V, and FLV. Audio inputs: MP3, WAV, OGG, M4A, AAC, and FLAC. Output is MP4 for MP4-family inputs, WebM for WebM, and MKV for legacy or flexible containers.

Related tools

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