Audio joiner

1. 1

   Add the files

   Drop in two or more. Each shows its length, and the joined length is added up as you go.

2. 2

   Put them in order

   Move a file up or down with its arrows, or take it out. Pick a crossfade if you want the files to blend.

3. 3

   Join and download

   Play the result to check the joins, then download the MP3 or WAV.

With the crossfade off, each file starts the moment the one before ends, which suits parts of one recording, such as chapters or a podcast's intro and episode.

A crossfade overlaps the end of one file with the start of the next, fading one out as the other comes in, which suits songs in a mix. The fades are shaped so the loudness holds steady through the overlap. Each overlap is at most half of the shorter file, so a short clip isn't faded away.

Every file is decoded, resampled to 44.1 kHz stereo and joined into one stream, so files with different formats, sample rates or channel counts join cleanly.

MP3 comes out at 192 kbps, small enough to share and plays everywhere. WAV keeps every sample uncompressed, at about 10 MB a minute, for editing further.

FFmpeg's concat demuxer joins files listed in a text file, one per line as file 'part1.mp3', and this command encodes the result once:

• ffmpeg -f concat -safe 0 -i list.txt -c:a libmp3lame -b:a 192k joined.mp3

No. The files are decoded, joined and encoded in your browser. Nothing is sent anywhere.

Yes. An MP3, a WAV and an M4A can go in one join, as long as your browser can play each of them.

Use the up and down arrows on each file. The files play in the order of the list, top to bottom.

WAV keeps everything. MP3 is encoded once more, at 192 kbps, since joining means decoding every file, MP3s included. If you'll edit the result further, pick WAV.

As many as you like. The files are decoded one at a time, so the memory it needs depends on the longest files, not on how many there are.