Add Background Music to Video in Your Browser

Adding music is not merely attaching a file to a video. A useful result has to decide which sound owns the listener's attention, how long the music should continue, whether an original voice stays audible, and how the track enters and leaves the picture. This page accepts one base video and one local audio source such as MP3, M4A, AAC, WAV, OGG, FLAC, or an audio-bearing video. Browser FFmpeg loops the selected background source so it can cover the base picture, applies the levels and fades you set, then writes a standard H.264 and AAC MP4. It is a focused handoff tool for a prepared video and prepared background file, not a substitute for a multitrack timeline.

1. 1

   Choose the picture and the approved background source

   Select the video whose picture must remain unchanged, then select a locally available background source. Listen to that source first and confirm that its rights, intended audience, language, and mood are appropriate. A looping track repeats from its first frame, so music with an obvious intro, ending, or hard loop point may need preparation in an audio editor before you use it here. A background file can be short; the tool repeats it to follow the video. It does not magically make an unsuitable loop sound seamless.

2. 2

   Choose mix, duck, or background only

   Mix both keeps the original video sound and the new bed at the two levels you choose. It is appropriate when the source already has useful ambience or a narrator that does not need special protection. Duck under original also preserves both tracks, but uses the base audio as a sidechain signal to reduce the music while that source is active; use it for spoken explainers when the original audio is reasonably clean. Background only ignores the original audio and is the right option for silent footage, music-led edits, or a base track you intentionally do not want to retain. Mix and duck need an audio track in the base video, while Background only does not.

3. 3

   Set levels, fades, and video quality before export

   The background slider controls gain before the AAC encode. Begin conservatively, usually around 25 to 40 percent for music beneath speech, because increasing a file that already peaks near full scale can create distortion after mixing. The original slider only applies when its track is kept. Set a small fade in and fade out to soften the entry and exit of the repeated bed. CRF and preset affect the H.264 picture re-encode, not the musical arrangement; lower CRF values preserve more image detail but make a larger MP4. After conversion, listen through the opening, a speech-heavy moment, the loop boundary, and the ending before sharing the result.

A background track can improve pacing, hide small gaps in room tone, and make a silent clip feel intentional. It can also make a tutorial exhausting if it competes with every spoken word. The usual failure is not a codec problem; it is an unclear relationship between the two tracks. A page that simply says add music leaves unanswered whether the camera microphone survives, whether the music is reduced while speech exists, and what happens after a short song ends. This tool presents those decisions as Mix both, Duck under original, and Background only rather than hiding them inside an export command.

The output is deliberately conventional: H.264 picture and AAC sound in an MP4 container. That makes a local result easier to check in ordinary players, browser previews, chat tools, and review systems. It does not provide loudness metering, licensed-music clearance, beat detection, stems, soundtrack editing, or delivery specifications for broadcasters. The practical value is smaller but real: one clear video, one clear bed, a controlled relationship between them, and a downloadable review file without sending source media to a conversion queue.

Mix behavior is the central setting. Mix both sums the original and background tracks. Duck under original uses compression to lower the bed when the source audio is active, but it cannot distinguish clean dialogue from wind, crowd noise, or an already-loud soundtrack. Background only is a replacement-style output and works for silent base videos. Background volume and original volume are gain controls, not a mastering meter. Fades are applied to the background source at the beginning and calculated end of the base video. CRF 23 with veryfast is a sensible local starting point; choose a lower CRF only when image detail needs more protection.

Verify that the final picture lasts as long as expected, the music begins at the intended level, and speech is still intelligible on headphones and a phone speaker. In duck mode, listen around pauses and loud words to make sure the music movement is not distracting. If the background source loops, listen at the repeat boundary rather than assuming it is invisible. Check the final few seconds for a smooth fade and make sure you selected Background only if the source video had no usable audio. Finally, confirm that music rights cover the place where the MP4 will actually be published, not merely an internal preview.

• Start background volume around 25 to 40 percent and listen on headphones before making it louder.
• Use Duck under original when speech is the priority; it compresses the bed while the original track is present.
• Use a short fade at the start and end so a looped track does not enter or stop abruptly.

The selected video and audio source are written into the browser-side FFmpeg workspace and the mixed MP4 is returned as a local download. The normal flow does not require an account, a cloud editing project, or a server conversion queue. That is useful for unreleased campaigns, internal tutorials, customer demonstrations, classroom material, and recordings that should not be uploaded merely to add one prepared track.

Local processing does not erase visible private information, validate music licenses, remove metadata, or decide whether a track is appropriate for commercial, educational, paid, or regional distribution. The original video may contain client data, faces, names, or confidential screens; the music file may have rights restrictions even when it was easy to download. Review both sources and the completed MP4 before distribution.

Use a timeline editor or audio workstation when you need to cut music to beats, place cues at specific frames, edit multiple regions, automate levels, remove breaths, repair noisy dialogue, use several background stems, or meet a regulated loudness target. Those jobs need meters, automation, and repeated review. Browser-local processing is also better for manageable files than for hour-long 4K recordings. For one base clip, one prepared bed, a repeated duration, visible levels, and a simple ducking decision, this tool keeps the job focused and easy to review.

• You need frame-accurate music edits, beat matching, multiple songs, keyframes, dialogue repair, or automated editorial decisions.
• The base clip has no original audio and you selected Mix both or Duck under original; choose Background only instead.