By Jason Snell

December 4, 2017 4:35 PM PT

Forecast: A must-have tool for Mac podcasters

Note: This story has not been updated for several years.

Marco Arment’s Forecast is a newly released (into a public beta) Mac MP3 encoding and tagging tool for podcasters. It’s a tool that Marco built a couple of years ago to serve his own needs, and for the last 18 months or so I’ve been using it (in a private beta) to encode most of the podcasts that I create. Here’s an overview of how Forecast works and what it does.

Forecast takes input files—generally uncompressed audio exported from an audio editing app in WAV format, though it can open other file formats—and outputs MP3 files for use in a podcast feed. This is nothing remotely new. What makes Forecast interesting is the details of how it encodes and tags those files.

First off, the encoding process itself: Forecast is extremely fast at encoding MP3 files for a few different reasons. At its heart, it’s using the common (and excellent) LAME MP3 encoder, but Forecast spreads the encoding job across all of your Mac’s processor cores. The result is that files encode much, much faster (in 29 percent of the time as standard LAME, in my tests, and 80 percent of the time of the iTunes encoder)—and your Mac’s fans will probably spin up briefly, because Forecast is pushing your processor to use all its power to do the job.

There’s also a perceptual trick that Forecast uses to make encoding seem quick: When you add a file to be encoded, encoding begins immediately in the background. By the time you edit your file’s metadata, the encode may have already completed in the background. The first time I used Forecast, I thought something had gone wrong—because when I typed Command-S to save the file, it just saved. There was no wait. The file had already encoded—it was waiting for me, the slow human, to finish typing in episode titles and show descriptions.

All the rest of Forecast is about tagging files to include things like the episode title, show art, and chapter data. Just about any MP3 app can add description tags, but only a handful support MP3 chapters. (Some others are Rogue Amoeba’s Fission and Thomas Pritchard’s Podcast Chapters.)

It turns out that the WAV file format includes support for markers—specific designations of events that happen at particular time codes—and that most audio editors (including Logic and Audition) that export as WAV files will export any markers found in that particular project. This means that in order to add chapters to my podcasts, I don’t need to add a step where I laboriously write down time code for all the events in the episode and then input them one by one into Forecast.

Instead, I just click the Plus icon next to the Marker label in Logic and add a marker. When I export that project to a WAV file and import it into Forecast, the app automatically reads the markers and converts them into chapters. I don’t need to do anything.

That said, Forecast also does support the manual entry of chapter times and the editing of chapter data, including title, URL, and custom per-chapter images. (Manually entering times is a little bit buggy—frequently I need to do it twice before it displays properly. I don’t do this a lot, but it’s an annoying bug I hope Marco will fix.)

There’s also a checkbox that allows for the creation of invisible chapters that don’t display in the episode’s chapter list, but do change the displayed art or link at a particular time. There’s a lot here, depending on how much work you want to do to add a rich media layer on top of your podcast.

Forecast also tries to save you time by recognizing that similarly named source files are probably part of the same podcast, and attempting to intelligently autofill data based on that assumption. When I add a file called theincomparable382.wav to Forecast, it realizes that this is almost certainly episode 382 of The Incomparable and automatically enters The Incomparable in the Podcast Title field, adds 382: to the Episode Title field, adds the right image to the show art, and even sets the proper MP3 output format—and all because it knows what I did when I encoded theincomparable381.wav last week. (This autofilling extends to URLs and art in chapters, too. If I have a regular sponsor for a podcast, Forecast is smart enough to remember the URL attached to those sponsorship chapters.)

For editors of sponsored podcasts, Forecast can detect your sponsorship chapters and export those out as separate files, ready to be sent to your ad network or sponsors as “airchecks”—i.e., proof that the ad spots aired as promised. There are also quick-copy features that let you quickly put the show’s duration or file size on the clipboard—apparently this is something Marco needs for one particular podcast host, though I’ve never needed to use those features myself. There’s also a feature that warns you if your audio file contains long amounts of silence—a sign that perhaps something is wrong with your podcast, so you might want to check it before posting.

If you’re a podcaster, you should give Forecast a try. It’s free, and a whole bunch of podcasters have been using it enthusiastically for more than a year, so it’s battle tested. I recommend it highly.

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