Audio Joiner combines 2 to 10 browser-decodable audio files into one PCM16 WAV in your browser, free, with no uploads, so you can prepare a single audio bed for any video project. The tool concatenates 2 to 10 audio clips in the exact order you choose and exports one downloadable WAV, with every step — file reading, decoding through the Web Audio API, channel concatenation, preview, and WAV encoding — running inside the current browser tab. Your source audio never leaves the device, which removes the upload step that most free online audio mergers require. The join is gap-free: the last decoded sample of one track is followed immediately by the first decoded sample of the next, with no inserted silence, overlap, crossfade, normalization, or transition. That behavior makes the tool well suited to assembling a complete audio bed — music intro, voiceover, sound effects, outro — that you can drop onto a video timeline as one track. The resulting WAV is an uncompressed little-endian RIFF/WAVE container, so it plays in any standard editor or player that accepts WAV, although its file size will typically be larger than the compressed MP3, AAC, or FLAC sources you started with.
Why Combine Audio Before Adding It to a Video
Most free video editors only let you place a handful of audio tracks on the timeline, and layering a music intro, spoken voiceover, ambient sound, and an outro sting across separate tracks can quickly crowd the mix. A common workaround is to bake everything down to one audio file outside the editor and then drop that single file onto the video. Audio Joiner is built for exactly that step: it takes the multiple clips you have already prepared — narration recorded in a voice app, background music downloaded from a royalty-free library, a couple of sound effects pulled from a sound pack — and stitches them into one WAV in the order you choose. Because the tool runs entirely in the browser through the Web Audio API, it is free to use without an account, and your source audio is never uploaded to a remote server.
The output WAV is a clean concatenation: channel arrays are copied into one buffer at tested cumulative frame offsets, then interleaved and written to a standard RIFF/WAVE container. That means the join is sample-accurate at the boundary — there is no gap, fade, or ducking applied — so any silence you hear between clips is silence that already existed in your source files. If you want a smooth transition between two pieces of music, you need to add that in a dedicated editor; Audio Joiner will not invent one for you.
Input Limits and Channel Requirements
Audio Joiner rejects selections that exceed its published budgets rather than trimming them silently, so checking these limits before you start saves time.
| Limit | Value |
|---|---|
| Number of files per selection | 2 to 10 |
| Per-file encoded size | 25 MiB (26,214,400 bytes) |
| Total selection size | 100 MiB (104,857,600 bytes) |
| Total decoded duration | 30 minutes |
| Total channel-samples | 30,000,000 across all channels |
| Channels per track | Up to 8 |
| Sample rate ceiling | 192 kHz |
| Channel count rule | Every track must match |
The channel-count rule is the one that surprises most readers. All decoded tracks must share the same number of channels — a mono voiceover and a stereo music track cannot be joined. Audio Joiner rejects the selection with a specific message rather than silently duplicating, dropping, averaging, or remapping channels. The same browser session also resamples sources to a single working sample rate through the Web Audio API, so the rate shown after decoding may differ from the rate stored in the original file. According to the MDN documentation for BaseAudioContext.decodeAudioData, decoding behavior depends on the codecs available in the current browser and operating system, which is why a recognized extension like .m4a or .webm does not guarantee that every variant will load in Safari, Chrome, or Firefox. A high-rate or multichannel selection can reach the 30 million sample budget before the 30 minute duration limit runs out, so planning a short test selection first is wise if you are unsure how your files decode.
Combine Audio Files for a Video in Your Browser
The workflow has three visible phases: pick the files, set the order, then preview and download the result.
- Open Audio Joiner and choose 2 to 10 audio files in a single selection. The file picker recognizes common MP3, WAV, M4A, AAC, Ogg, WebM, and FLAC names and MIME types, but a recognized extension does not guarantee the codec will decode. Damaged, encrypted, incomplete, mislabeled, or unsupported files produce a clear error.
- Wait for the browser to decode each file through a shared AudioContext. Track metadata such as decoded duration and channel count appears once decoding finishes. Selecting the same files again works because the file input is reset after every choice.
- Use the Move up and Move down controls next to each track until the list reflects the order you want in the final WAV. Reordering updates both the decoded buffer array and the visible list, and it clears any older WAV so a stale preview cannot claim a previous order.
- Select Join in this order. The tool validates the plan against the budgets above and concatenates the channel arrays at tested cumulative frame offsets. If anything fails the plan check — wrong channel count, sample rate above 192 kHz, more than eight channels, more than 30 minutes, more than 30 million samples — the selection is rejected with a specific message rather than being silently shortened, downmixed, downsampled, or omitted.
- Preview the resulting PCM16 WAV in the built-in player to confirm the order, joins, and channel playback. Golden stereo fixtures in the underlying test suite use different values in the left and right channels across two tracks, which proves that track order and channel identity survive the join.
- Download the WAV file. The download is a freshly encoded little-endian RIFF/WAVE file with interleaved signed 16-bit PCM samples, ready to import into your video editor as a single audio track. Imported as one clip, the combined audio plays back from start to finish without track-boundary edits inside the video timeline.
Keep your original source files until you have confirmed the downloaded WAV plays back at the expected duration, in the expected order, with the expected left and right channels. Audio Joiner never modifies or replaces your inputs, and selected files plus the finished WAV use temporary local object URLs that are released when replaced or when the page closes.
What the Output WAV File Contains
Every download is a new PCM16 WAV, not a wrapper around your originals. The shared encoder writes a 44-byte header with the RIFF size, WAVE and fmt identifiers, PCM format tag, channel count, decoded sample rate, byte rate, block alignment, 16-bit depth, data identifier, and exact data byte length. Float samples are clipped to the range -1 through 1; negative full scale maps to -32768, positive full scale to 32767, and non-finite values are written as silence. Channels are interleaved in frame order during write-out, so a stereo file keeps left and right channels paired the way they were decoded.
The output does not preserve the original codec, bitrate, encoder settings, tags, album art, chapters, cue points, loop points, loudness fields, timestamps, or other container metadata. It is a static PCM representation of the decoded samples, and because PCM16 WAV is uncompressed, the file size will usually be substantially larger than the compressed sources you uploaded. A 3-minute stereo WAV at 44.1 kHz works out to 44,100 samples per second × 2 channels × 2 bytes × 180 seconds = 31,752,000 bytes, or roughly 30 MiB, regardless of whether the source was a 128 kbps MP3 or a lossless FLAC.
When Audio Joiner Is the Wrong Tool
Audio Joiner is a concatenator, not an editor. If you need to trim a recording to a precise start and end time before joining, Audio Cutter extracts that time range and downloads a PCM16 WAV of its own. If you need fades between clips, loudness matching, dynamic compression, channel conversion between mono and stereo, compressed output formats, or sample-level repair, plan to finish the job in a dedicated audio editor after you have exported your WAV.
For background music on a slideshow, a single narration over a music bed, or a podcast-style voice track with intro and outro sting, Audio Joiner is the fast local step that produces the single audio file you can drop onto the video timeline. Open it in your browser, add your clips in order, and you have a free, locally produced WAV ready for the video project — no uploads, no subscription, no codec server. Every stage, from picking the files to encoding the final RIFF/WAVE container, runs in your tab using the same AudioContext that decoded the sources, which keeps the workflow predictable and reproducible across sessions.