Why Do This in Your Browser?
Concatenating audio files is conceptually trivial — append one to the next — but the implementation has a footgun: if the source files differ in sample rate, bit depth, or channel count, naive concatenation produces clicks, pops, or speed changes at the boundaries. Cloud audio mergers handle this by uploading both files, normalizing on a server, then sending the result back. The normalization is the actual work.
FFmpeg.wasm normalizes (resamples, rechannels, requantizes) and concatenates in one pass with the `concat` filter. The result is a clean merged file, with or without crossfade at the boundaries. All local, no uploads.
How It Works
Drop multiple files. The tool extracts each file's sample rate, channel count, and codec, then displays them in a reorderable list. Drag rows up/down to set the order; click ✕ to remove. Choose 'No crossfade' (hard cuts) or set a crossfade duration (50–5000ms).
When you click 'Merge', FFmpeg.wasm runs the `concat` filter for hard cuts or the `acrossfade` filter for fades. All inputs are normalized to the target sample rate (44.1kHz default, 48kHz optional) and channel count (stereo default). Output codec matches the first input's codec unless you override.
Tip: Pre-trim each input clip with the Audio Trimmer before merging — cleaner cuts make the crossfade sound better. After merging, run a final normalization pass with the Audio Normalizer to even out level differences across the merged segments. For combining two mono files into a stereo pair (channel-merge) rather than concatenating clips end-to-end, the Audio Channel Tool handles that case.
Common Use Cases
How We Compare
Honest read on free, paid, and self-hosted options for this kind of job: