Castos
Free Podcast Tool

Join Audio Files Online

Combine intro, episode, and outro files into one podcast-ready MP3. Free, private, and entirely in your browser.

Your audio stays on your device. Nothing is uploaded or stored.

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How To Join Audio Files Online

  1. Step 1

    Choose Your Audio Files

    Select two or more MP3, WAV, M4A, AAC, OGG, or FLAC files. Each one stays in your browser and is never uploaded.

  2. Step 2

    Put Them In Order

    Use the up and down arrows to arrange your files, preview any of them, and remove ones you don't need.

  3. Step 3

    Join And Download Your MP3

    Click Join & Export MP3 and download one podcast-ready file. Turn on a short crossfade for smoother transitions between tracks.

One File Instead Of Several

An intro, the main recording, a mid-roll ad, and an outro usually live as separate files. Combining them by hand means opening an editor just to lay tracks end to end. This tool does the same job directly in your browser, no editing software or account required.

Nothing Leaves Your Device

Every file you add is joined locally. Your audio is never sent to a server while you reorder tracks or export the result. Close the tab and the working files disappear.

Podcast-Ready MP3 At 128 kbps

Every joined file is exported as an MP3 at 128 kbps, a standard podcast bitrate that keeps spoken audio clear at a practical file size. There is no format menu to configure and no extra setting to second-guess before you upload it to a host.

Audio Joined? Publish Your Podcast In 3 Steps

  1. Upload a new episode in Castos

    Upload The MP3

    Create a show in Castos and upload your joined MP3 with your episode title, description, and artwork.

  2. Fill in podcast details in Castos

    Get Your Feed And Website

    Castos creates the RSS feed podcast apps need and a customizable site where listeners can find every episode.

  3. Link your feed to each podcast directory

    Publish Everywhere

    Submit your feed to Apple Podcasts, Spotify, and other directories once. Future episodes are distributed automatically.

Frequently Asked Questions

How do I join multiple audio files into one MP3?
Choose two or more MP3, WAV, M4A, AAC, OGG, or FLAC files, then use the up and down arrows to put them in the order you want. Click Join & Export MP3 and your browser creates one 128 kbps MP3 in that order.
Is this audio joiner free?
Yes. This joiner is free, requires no account, and adds no watermark. The output is a standard 128 kbps MP3.
Is my audio uploaded anywhere?
No. Your browser joins the files on your device with WebAssembly. Castos never receives or stores your audio. The first export may take a moment because the browser needs to load the joiner first.
Can I add a crossfade between tracks?
Yes, if every file you've added is at least 2 seconds long. Check Add a short crossfade between tracks and each transition blends the end of one file into the start of the next over about a second instead of cutting sharply.
How many files can I join, and how do I reorder them?
You can join up to 20 files. Use the up and down arrows next to each file to move it earlier or later in the sequence, or the x to remove one.
Why is the export always an MP3 at 128 kbps?
128 kbps is a standard podcast bitrate. It keeps spoken audio clear at a practical file size for hosting and listening, so there is no format menu to configure or second-guess.

Related Tools

Publish Your Joined Episode With Castos

Upload your MP3, create your podcast feed, and distribute every episode from one place.

Get Started For Free