How to merge audio files with crossfade — browser tool
- Step 1Drop exactly two files — Add the two tracks you want to blend (any of
MP3, WAV, FLAC, M4A, OGG, Opus). Crossfade is a two-file operation — to crossfade across several tracks, you'll repeat this pairwise. - Step 2Confirm the order — The first file in the list fades out; the second fades in. Files crossfade in list order — if they're reversed, remove one with its X and re-add. Check the durations so the overlap math makes sense.
- Step 3Set the crossfade duration — Use the Crossfade (s) field (0-10, step 0.5). A typical music blend is 2-4 seconds; a quick smooth join is 0.5-1s. Setting 0 produces a hard join (no overlap).
- Step 4Pick the output format — MP3/M4A for sharing (192 kbps), WAV/FLAC for a lossless master. The crossfade itself is identical regardless of format.
- Step 5Run the crossfade — FFmpeg-WASM normalises both inputs to 48 kHz stereo, applies
acrossfade=d=<seconds>, and encodes once — all locally on your CPU. - Step 6Download and check the seam — Save
merged.<ext>and listen around the overlap point (roughly at the first file's length minus the crossfade duration). The total length should be input1 + input2 minus the crossfade window.
Crossfade behaviour by file count
The single most important rule: crossfade engages only for exactly two files.
| Files merged | Crossfade > 0 | What happens |
|---|---|---|
| 2 | Yes | acrossfade=d=<s> overlaps tail of file 1 with head of file 2 |
| 2 | 0 | Plain gapless hard join (no overlap) |
| 3 or more | Yes | Crossfade IGNORED — falls back to end-to-end concat |
| 3 or more | 0 | End-to-end concat |
Crossfade duration guidance
The control accepts 0 to 10 seconds in 0.5s steps. These are practical starting points.
| Use case | Suggested crossfade | Notes |
|---|---|---|
| Two songs (DJ blend) | 3-6 s | Longer feels smoother; match to the outro/intro energy |
| Music intro into speech | 1-2 s | Short so the first words aren't buried |
| Two ambient/loop beds | 4-8 s | Long overlaps hide the seam entirely |
| Quick seamless join | 0.5-1 s | Just enough to kill the click of a hard cut |
| No blend (hard cut) | 0 | Gapless concat |
Tier limits (audio family)
Crossfade is a two-file merge; both files count against the batch and each against the size/duration caps.
| Tier | Max file size | Max duration / file | Files per batch |
|---|---|---|---|
| Free | 50 MB | 30 min | 1 |
| Pro | 200 MB | 120 min | 10 |
| Pro-Media | 100 GB | Unlimited | 100 |
| Developer | 100 GB | Unlimited | Unlimited |
Cookbook
Real two-track crossfades with inputs, the crossfade setting, and the resulting length. Output length = sum of inputs minus the crossfade window.
Crossfade two songs into one mix
Blend the end of one track into the start of the next over 4 seconds for a smooth DJ-style transition.
Inputs: track-a.mp3 44100 Hz 2ch 3:30 track-b.mp3 48000 Hz 2ch 3:10 Options: crossfade 4.0, format MP3 Output: merged.mp3 48000 Hz 2ch 6:36 (3:30 + 3:10 = 6:40, minus 4s overlap = 6:36)
Short blend to remove a hard-cut click
Two voice clips that hard-cut with an audible click. A 0.5s crossfade smooths the join without altering content.
Inputs: clip1.wav 0:42 clip2.wav 0:38 Options: crossfade 0.5, format WAV Output: merged.wav ~1:19.5 (lossless, seamless join)
Music intro fading into the first words
A 2-second crossfade lets the intro music duck under the start of speech instead of cutting dead.
Inputs: intro-music.mp3 0:12 vo-open.mp3 0:25 Options: crossfade 2.0, format MP3 Output: merged.mp3 ~0:35 (music blends into voice over 2s)
Crossfade across three tracks (do it in pairs)
Crossfade only works on two files. For A->B->C with blends, crossfade A+B first, then crossfade that result with C.
Step 1 crossfade-merge-audio-browser A + B (crossfade 4.0) -> AB.wav Step 2 crossfade-merge-audio-browser AB.wav + C (crossfade 4.0) -> ABC.wav Output WAV between steps to avoid stacking MP3 loss.
Crossfade two ambient beds for a loop
Two long ambient recordings blended over 8 seconds hide the transition for background/loop use.
Inputs: rain-bed.flac 5:00 forest-bed.flac 5:00 Options: crossfade 8.0, format FLAC Output: merged.flac ~9:52 (lossless, transition buried)
Edge cases and what actually happens
Three or more files with crossfade set
IgnoredCrossfade only applies when exactly 2 files are merged. With 3+ files the crossfade value is silently dropped and the tool concatenates end-to-end. To crossfade a chain of tracks, merge them in pairs (A+B, then AB+C). The UI shows a note about this when crossfade > 0.
Crossfade longer than the shorter track
Rejectedacrossfade needs both tracks to be at least as long as the crossfade window. If the overlap (e.g. 10s) exceeds the length of a very short clip, FFmpeg errors out. Reduce the crossfade duration to less than the shorter file's length.
Only one file dropped
RejectedA crossfade needs two tracks (Audio merger needs at least 2 files.). To fade a single file in or out at its ends, use fade-in-out instead — that's a one-file operation.
Inputs at different sample rates
By designBoth files are resampled to 48 kHz stereo before the crossfade, so a 44.1 kHz and a 48 kHz track blend without a pitch/clock mismatch at the overlap. This normalisation is automatic.
Output is shorter than the sum of inputs
ExpectedA crossfade overlaps the two tracks, so the output length equals input1 + input2 minus the crossfade duration. A 4-second crossfade on two 3-minute tracks yields ~5:56, not 6:00. This is correct, not lost audio.
Crossfade set to 0
Hard joinCrossfade of 0 produces a plain gapless concat with no overlap — identical to a hard merge. Set a value above 0 (the field steps by 0.5) to actually blend the tracks.
One track is mono
ExpectedA mono input is upmixed to stereo before the crossfade, so the blended output is stereo. There's no mono output option in the merger.
Equal-power vs linear curve not selectable
By designThe crossfade uses FFmpeg acrossfade's default curve; the UI doesn't expose curve-shape (equal-power/linear/log) controls. For most music and speech blends the default sounds natural. If you need a specific curve, you'd need a full DAW.
File over the tier size/duration cap
BlockedEach input must fit the tier caps (Free 50 MB / 30 min; Pro 200 MB / 120 min). A long song over the cap blocks the crossfade. Trim it with audio-trimmer or upgrade.
Free tier only allows 1 file
Tier limitA crossfade needs 2 files, but Free's audio batch limit is 1. Crossfading therefore needs Pro or higher (10 files per batch). The crossfade itself runs identically at every tier.
Frequently asked questions
How many files can I crossfade at once?
Exactly two. The acrossfade filter only engages when two files are merged. With three or more, the crossfade is ignored and a plain end-to-end concat is used instead. To crossfade across more tracks, merge them in pairs (A+B, then the result with C, and so on).
How long can the crossfade be?
0 to 10 seconds, in 0.5-second steps. A value of 0 is a hard join; 2-6 seconds is typical for a music blend. The crossfade can't be longer than the shorter of the two tracks, or FFmpeg will error.
Why is my output shorter than the two files combined?
That's how a crossfade works — the two tracks overlap, so the output length is input1 + input2 minus the crossfade duration. A 4-second crossfade removes 4 seconds of total length because that's the overlap window. No audio is lost; it's blended.
Are my tracks uploaded?
No. The crossfade runs in your browser on FFmpeg 8.1 (WebAssembly). Your audio never leaves the device — there's no server processing and no upload wait.
Can I choose the crossfade curve (equal-power, linear)?
No — the tool uses FFmpeg acrossfade's default curve and doesn't expose a curve-shape control. The default sounds natural for most music and speech blends. For precise curve control you'd need a DAW.
Can I crossfade files of different formats?
Yes. Both inputs are normalised to 48 kHz stereo before the crossfade, so a 44.1 kHz MP3 and a 48 kHz WAV (or any mix) blend cleanly with no pitch or clock mismatch at the overlap.
Which file fades out and which fades in?
The first file in the list fades out; the second fades in. Order follows the file list (the order you added them). There's no reorder handle, so if it's backwards, remove one file with its X and re-add it in the right order.
What output format should I use for a DJ mix?
Output WAV or FLAC to keep the master lossless, especially if you'll chain pairwise crossfades across many tracks (re-encoding to MP3 at each step would stack loss). Export the final mix to MP3 (192 kbps) at the end, or re-target with bitrate-changer.
What's the difference between crossfade-merge and fade-in-out?
Crossfade-merge blends two separate files where they meet. fade-in-out applies a fade at the start and/or end of a single file — no second file involved. Use fade-in-out to soften one track's edges; use this tool to blend two tracks together.
Can I crossfade three or more songs into a continuous set?
Yes, but pairwise. Crossfade the first two into one file, then crossfade that result with the third, and so on. Output WAV/FLAC between steps so you don't accumulate MP3 re-encode loss across the chain.
My crossfade failed with a short clip — why?
The crossfade window can't be longer than the shorter track. If you set, say, 8 seconds but one clip is only 5 seconds, acrossfade errors. Lower the crossfade to under the shorter file's duration.
Does the crossfade re-encode my audio?
Yes — like all merges here, both inputs are decoded, normalised to 48 kHz stereo, crossfaded, and re-encoded once (MP3/M4A at 192 kbps, or lossless WAV/FLAC). For lossless work, choose WAV or FLAC output.
Privacy first
Every JAD Audio tool runs entirely in your browser via FFmpeg (WebAssembly) and RNNoise. Your audio files never leave your device — verified by zero outbound network requests during processing.