Merge audio files without uploading them anywhere.

Questions

Do my files get uploaded?

No. Every file you drop in stays on your device. Decoding uses the browser's built-in Web Audio API, the merge is just array math on the in-memory PCM samples, and the MP3 encoding runs locally via a ~50KB JavaScript library (lamejs). We never see your audio. This matters when you're stitching together voice memos, interview recordings, sermon clips, podcast segments, or anything else you'd rather not hand to a stranger's server.

What formats can I merge?

Anything your browser can decode: MP3, WAV, M4A, FLAC, OGG, AAC. Plus video files — MP4, MOV, WebM — because the Web Audio API extracts the audio track from those automatically. Drop a mix of audio clips and a video file together; we'll merge the audio from all of them. Output is MP3 (default 192 kbps, bitrate selectable) or WAV (lossless).

What if my files have different sample rates?

We'll let you know rather than merging silently. Different sample rates can't be concatenated directly without resampling, and quality varies widely depending on the resampling algorithm — so we don't guess. If you see this error, convert all files to the same sample rate first (44.1 kHz is the most common) using our WAV→MP3 or MP3→WAV converter. Most audio files are already 44.1 kHz, so this comes up rarely.

Can I add silence between tracks?

Yes — the Silence Between Tracks dropdown lets you insert 0.5, 1, 2, or 3 seconds of silence between each clip. Useful when you're building a single audio file from chapter segments (audiobook chapters, podcast segments) and want a clear break between each. The silence is just literal zeros in the PCM buffer, so it adds no audible artifact, just a clean pause.

What about crossfading between tracks?

Not in this version — every clip is concatenated directly (with optional silence). Crossfading is on the roadmap but adds UI complexity around fade duration and curve shape. For now, if you need crossfades, do them in a desktop tool like Audacity. For most use cases — combining voice memos, joining audio chapters, building a single file from podcast segments — direct concatenation is what you want.

Can I reorder the tracks?

Yes. Each file in the list has Up and Down arrows next to it. Click them to shuffle clips into the order you want. The X button removes a clip from the merge entirely. The order in the list is exactly the order they'll be merged.

What's the upper limit?

Up to 50 files per merge, 300MB per file, 4 hours of total merged audio. Beyond that the browser may run out of memory holding everything in RAM simultaneously. If you need to merge longer or more files, split the job into batches and merge the batches.

Will the output sound the same as the input MP3s?

The output is one decode-and-re-encode step away from the inputs. MP3 inputs get decoded to PCM, merged in PCM space, then re-encoded. That's one extra lossy step per file. The audible difference at 192+ kbps is negligible for most listeners, and inaudible at 320 kbps. For absolute lossless merging, pick WAV as the output — no re-encoding loss happens then.

Why merge in the browser instead of using Audacity?

Audacity is the right tool for serious multitrack editing. This is for the common case: you have 3-10 audio files, you want them concatenated into one file, you don't want to install software. The Audacity workflow for this exact task takes 8-12 clicks and an installation. This takes about 30 seconds.