Add audio to video
The right music. A clearer voice. Put your own sound with your video, or mix it under the original. Line it up, listen and save.
Bring your sound. Shape the timeline. Save one video.
Add audio to video is in your dock. Everything you started is still there.
Same picture. Your sound.
Layer sound. Cut a moment. Put every clip where it belongs.
Start with your picture.
Add your video, then shape its soundtrack below.
MP4MOVWEBMMKVM4V
Every sound, in its place.
Not saved
Not saved
Drag clips to place them. Drag their edges to trim. Click the ruler to set the playhead.
Move a long recording left to use a later part. Sound outside the video is left out. New audio starts at the playhead.
Peak protection keeps a loud mix from clipping.
Files, clips, timing, levels and speed stay in this tab.Only your file format preference saves privately.Saving details
How to add music or audio to a video
Bring your picture and sound
Open one video and up to eight audio files, in either order. Or try the example. Your files stay on your device.
Make them work together
Mix or replace the original sound. Drag, trim and split audio clips. Set their levels and speed, then listen.
Save the finished video
Choose an available format and press Save video. The picture is copied without re-encoding. Your source files stay unchanged.
Using the soundtrack studio
Work with one video and several audio clips. Move long recordings before the picture’s start, layer sounds or cut a recording into pieces.
Open your files
Choose a video and Choose audio open the pickers. Open files in the file bar accepts a video and several audio files together. Add audio brings in more sound. New clips start at the playhead.
- Drop files anywhere on the page, paste them or use Try an example.
- Select a named audio source below the timeline to find its clip. The video chip opens its picker.
- Change replaces the selected source in every clip that uses it and resets those source trims.
- The × beside an audio source removes that file and all its pieces. Clear removes the project and its undo history.
- Files, edits and speed settings stay in this tab. Only Save as can save to your private account.
Place, trim and cut audio
Drag the middle of a clip to move it. Drag either edge to trim. The timeline scrolls as you hold a dragged clip near an edge.
A negative Start in video is useful for long recordings. With an eight-second recording at −4 seconds, audio second four plays at video zero. The part before the picture is left out.
| Control | What it changes |
|---|---|
| Start in video | The selected piece’s position, in finished video seconds. Negative values put part of the piece before the picture. |
| Play for | The piece’s duration on the finished timeline. Without Repeat, it must fit the remaining source audio. |
| Trim source | Source in and Source out choose the audio range. Changing them resets this piece’s slice offset and duration. A split piece’s actual source position is shown above these controls. |
| Split at playhead | Cuts the selected piece into two at the playhead. Move either piece independently. Repeated clips keep their source phase across the cut. Existing fades stay continuous. |
| Duplicate / Delete clip | Make another piece from the same source, or remove only the selected piece. Deleting a piece leaves its source file available. |
| Undo / Redo | Restore up to 60 clip edits. Opening, replacing or removing source files begins a new edit history. |
| Snap | Align dragged clips to the playhead, picture edges and other clip edges. Hold Alt while dragging to bypass it. |
| Timeline zoom / Show playhead | Fit the picture, fit every clip or zoom in. The arrow button brings the playhead back into view. |
Click the ruler to place the playhead before a cut. The video starts at zero. Only audio inside its finished duration is saved.
Balance the sound and change speed
Mix both keeps your original sound alongside all added clips. Replace leaves the original sound out. Each selected clip has its own volume, speed and fades.
| Control | What it changes |
|---|---|
| Original sound | The original track’s level, from 0% to 100%. It is off in Replace and unavailable on a silent video. Up to eight original channels are mixed to stereo. |
| Clip volume | The selected music, voiceover or sound effect’s level, from 0% to 100%. Overlapping clips are mixed together. |
| Video speed | Changes picture timing and its original sound from 0.5× to 4×. A 12-second video at 2× saves as six seconds. Added clips keep their own timeline positions and speeds. |
| Audio speed | Changes only the selected piece, from 0.5× to 4×. Speed changes pitch. There is no pitch-preserving time stretch. |
| Repeat to fill the video | Repeats the selected source range. A split or trimmed repeated piece keeps its own explicit duration. |
| Fades | Apply Fade in and Fade out to the piece’s ends, from 0 to 10 seconds. Trim a piece to the video’s end if its fade should finish there. Long fades can overlap. |
| Peak protection | If the rendered sample peak exceeds 0.98, all levels are lowered together. This preserves your balance. It is not a LUFS or true-peak measurement. |
Listen before saving
Play preview works as soon as a video is open. Your mix uses the same rendered audio buffer as the saved file. Choose Original to compare the source at its original level. Switching to a prepared view keeps playback running. The counter shows finished video time.
- The timeline slider seeks through the whole video. The waveforms show audio activity, not loudness targets.
- Sound on or Sound off controls your preview speaker. It does not mute the saved video.
- A level or timing edit briefly pauses a playing mix. Playback resumes with the updated sound when you finish the change. Clip edits do not interrupt Original playback. A video speed change updates both views.
- Narrow, Wide or Full at the top right gives the studio more room. Close (×) or Escape returns to the page.
If the original audio cannot be prepared, its format and a retry appear under Original sound. The tool tries both local decoding paths first. It keeps your edits. Choose Replace explicitly if you want to save without that track.
Save and continue
Save as offers containers that can hold your existing picture codec and new sound. MP4 uses AAC audio. WebM uses Opus. Both save stereo sound at 48 kHz with a 192 kbps target.
Save video creates a new file. Cancel stops preparation or export and keeps your open work. Open in passes the result to another floi tool. Share offers File Transfer and supported device sharing options.
Keyboard controls
Use the controls with Tab. The timing fields accept decimal seconds.
| Key | Action |
|---|---|
| Ctrl / ⌘ + O | Open the shared file picker. |
| Ctrl / ⌘ + S | Press the available Save video button. |
| ← / → on a clip or trim handle | Move the piece or trim its edge by 0.1 seconds. Hold Shift for one second. Home on a piece returns its start to zero. |
| Delete / Backspace on a file chip | Remove that file. |
| S / Delete on the timeline | Split the selected piece at the playhead, or delete that piece. |
| Ctrl / ⌘ + Z | Undo a clip edit. Add Shift to redo. Text fields keep their usual editing shortcuts. |
Limits and supported files
Use one video up to 300 MB and eight audio sources up to 100 MB each. Every source can be up to five minutes. Combined source audio is limited to ten minutes, with up to 24 pieces. The finished video can be up to ten minutes at 0.5×.
This studio does not record a voiceover, find stock music or automatically lower music during speech. Repeats have no crossfade. Use SDR video. Added audio must be mono or stereo. Original sound with up to eight channels is mixed to stereo. Browser memory can run out below the file limits. The primary picture and audio tracks are used; extra tracks, embedded subtitles and chapters are left out. This is not a metadata scrubber.
The audio is decoded and encoded again. Copied picture packets preserve their encoded quality, but container metadata can differ. A rotated video needs a container that preserves its transformation. HDR is unsupported. In a stereo downmix, centre and surround speakers are included. The LFE channel is left out.
Use music you own or have permission to use. This tool cannot grant a licence or change an existing post on a social platform. Check the whole saved video before publishing.
Frequently asked questions
How do I add music to a video for free?
Open your video and a music file. Choose Mix both to keep the original sound, or Replace to use only the music. Listen with Play preview, then press Save video. You do not need an account, and the result has no watermark.
Can I replace the audio without losing video quality?
Yes, when an available output container supports the picture codec. The tool copies the encoded video packets. At 1×, it retains their timing. Changing video speed changes their timestamps. It does not resize or re-encode the picture. The audio is rendered and encoded again as AAC or Opus, so this is not a lossless audio operation.
Can I cut and layer several audio files?
Yes. Add up to eight audio files. Each gets a clip you can position independently. Place the playhead and press Split at playhead, then move or delete the pieces. You can use up to 24 pieces, with separate volume, speed and fades. Clip edits support Undo and Redo.
Can I add background music and keep someone speaking?
Choose Mix both. Leave Original sound at 100% and start each Clip volume around 25%. Listen through the loudest part and adjust by ear. This tool does not automatically detect speech or lower music during it.
What happens when the song and video have different lengths?
Drag a long recording left of zero to use a later part. Move a short clip right to delay it. Trim the edges or enter exact times. Repeat to fill the video loops a selected source range. Sound outside the picture is left out. Video speed sets the finished picture duration.
Can I put cleaned audio back onto the original video?
Yes. Open the original video and your repaired soundtrack. Choose Replace, set Clip volume to 100%, and turn looping and fades off. Check the timing at both ends before saving. Noise removal should preserve duration; removing pauses changes it and needs matching picture edits.
Does it work on a phone, and which files can I use?
The interface fits a phone or a narrow desk window. Codec and memory support depend on the browser. Open SDR MP4, MOV, M4V, WebM or MKV video up to 300 MB, plus mono or stereo audio up to 100 MB. Each source file can be up to five minutes. Use up to eight audio files, ten minutes of combined source audio and 24 edited pieces. A 0.5× video can produce up to ten minutes. MP3, WAV, M4A, AAC, Ogg, Opus and FLAC work when the browser can decode them.
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