About Audio Joiner
AntiUpload's Audio Joiner concatenates 2+ audio files into a single output, with three optional transition modes between clips: hard cut (default, just concat them end-to-end), crossfade (chained acrossfade filters, each pair overlaps over the configurable duration), or silence gap (anullsrc-generated quiet stretches inserted between every pair of inputs). Pick MP3, WAV, OGG, M4A, or FLAC for the output format and bitrate (for lossy formats). The whole pipeline runs in your browser via FFmpeg WASM — no upload, no file-size limit, no watermark, no ads.
Every input gets pre-normalised to 44.1 kHz stereo fltp before the join. FFmpeg's concat and acrossfade filters require uniform sample rate, channel layout, and pixel format across all inputs; mixing a mono podcast with a stereo song without normalisation produces silent or garbled output. We dodge this entire class of bug by pre-resampling every input at the same step. The trade-off: mono inputs get upmixed to stereo (the mono signal duplicated to both channels) which is technically a small quality concession but invisible in practice.
Three transition modes, mutually exclusive (engine enforces — you can't set both crossfade and gap to non-zero values simultaneously). **Hard cut**: clips concatenate end-to-end with no transition. Output length = sum of inputs. **Crossfade**: chained `acrossfade` filters fade between each pair of clips. Output length = sum − (N-1) × crossfadeSec. Smoothest transition, but creates ~1-2 seconds of overlap between distinct songs — pick this for mixtapes / DJ-style joins. **Gap**: silence inserted between each pair via `anullsrc`. Output length = sum + (N-1) × gapSec. Best for podcast intro / outro spacing, chapter breaks, mixtape pauses.
How it works
- Drop 2 or more audio filesAccepts MP3, WAV, M4A, OGG, FLAC, AAC, OPUS. Mixed formats OK — the tool normalises each before joining. Concatenation order follows file-picker order (usually alphabetical).
- Pick the output formatMP3 for compatibility, WAV for editing, M4A for Apple, FLAC for lossless. Bitrate picker appears for lossy formats (MP3 / OGG / M4A); WAV / FLAC are lossless and don't need a bitrate.
- Optionally pick a transition: crossfade or silence gapCrossfade overlaps clips over 0.5 / 1 / 2 seconds for smooth mixtape-style joins. Gap pads clips apart with 0.5 / 1 / 2 / 3 seconds of silence — useful for podcast intro / outro spacing. Mutually exclusive — pick one or neither.
- Click Join filesRe-encoding runs through the selected codec with the chosen bitrate. Output sample rate is 44.1 kHz stereo regardless of input. Processing is roughly proportional to the total output duration.