The Apple Watch desperately needs standalone podcast playback, especially with the LTE-equipped Series 3, which was designed specifically for exercising without an iPhone.

Believe me, I’ve tried. But limitations in watchOS 4 make it impossible to deliver standalone podcast playback with the basic functionality and quality that people expect.

Deal-breaker: Progress sync

Unlike on iOS, Watch apps aren’t allowed to play audio in the background and continue running.1

The only way to continue playback in the background on watchOS 4 is to use the WKAudioFilePlayer API. This is unsuitable for podcast players in its current state for one big reason:

It takes audio playback out-of-process, suspending the host app indefinitely during playback, and does not wake up the host app to notify it of playback progress or other relevant events like pausing, seeking, or reaching the end of an episode.

Since most podcast listeners also listen on their iPhone, the Watch needs to sync each episode’s listening progress with its iPhone app or a web service. But if you reach the end of a workout and pause playback without launching the podcast app, such as with a headphone “pause” button, turning off your headphones, removing your AirPods, or using the Now Playing app on the Watch, there’s no guarantee that the podcast app will be notified of your progress anytime soon. So when the user later goes to the iPhone app to continue playback, progress will be lost, or episodes’ state (played, deleted, recommended, etc.) will be wrong.

Minimum fix: During WKAudioFilePlayer playback, wake the host app to let it record progress periodically (ideally at least every minute) and on state-change events, such as pausing, seeking, and reaching the end of a file.

Better fix: Let apps continue running in the background indefinitely while they’re playing audio with WKAudioFilePlayer , just as workout apps can, so they can track their own state.2

To achieve the minimum experience-quality level that Apple and Overcast customers expect, watchOS and WKAudioFilePlayer also need a few more changes:

Volume control API or widget

Overcast’s top request for the Watch app by far is volume control via the Digital Crown, both for iPhone and Watch playback (when I offered it). It’s especially necessary for standalone Watch playback, as there’s very little access anywhere in watchOS to the concept of the system volume level.

Fix: An API to set the volume level, or a system UI widget for volume control like iOS’ MPVolumeView .

The lack of volume control is especially damaging with watchOS 4’s great new “Auto-launch Audio Apps” setting. If you’re playing audio from an iPhone app and have its corresponding Watch app installed, that Watch app shows by default when your Watch screen activates. If you don’t have its Watch app installed, the built-in Now Playing app shows instead.

In the last few days since watchOS 4’s launch, I’ve had dozens of users tell me that they’ve uninstalled Overcast’s Watch app just to force the Now Playing screen to auto-launch instead, just so they could have quick access to volume control.

Output-device presence, switching

WKAudioFilePlayer will not play to the Watch’s built-in speaker — it only plays to headphones connected to the Watch via Bluetooth. If playback is attempted without headphones connected, WKAudioFilePlayer just silently fails to play, without returning any errors.

Making matters worse, there appears to be no way to reliably detect the presence or absence of a suitable Bluetooth output device to avoid this.

Another common user request for Watch audio apps is an AirPlay output control. The rise of AirPods has increased this need and exacerbated the output-device-presence issue, as their multi-device sharing behavior leads to less certainty by the user about which device they’re currently connected to, and a more frequent need to manually select them on the current device.

Minimum fix: Fix the error-reporting behavior of WKAudioFilePlayer when suitable play conditions aren’t met, and provide a way to detect the presence or absence of a suitable audio-playback device so our apps can relay this information to the user.

Better fix: Also provide a standard AirPlay UI control, possibly integrated with the volume control, again like MPVolumeView on iOS.

Next/previous-track commands

Podcast listeners expect previous- and next-track buttons on headphones, cars, and the Now Playing app to perform 30-second seek operations instead of changing episodes completely. On iOS, MPRemoteCommandCenter lets apps respond to these commands however they want.

WKAudioFileQueuePlayer provides no such customization, ignores previous-track commands, and forces next-track commands to skip to the next audio file, losing any progress in the current one — and if there isn’t a next file in the queue, it stops playback completely. And all of this happens without waking the host app.

Minimum fix: Wake the host app whenever the current queue item changes in WKAudioFileQueuePlayer .

Better fix: Bring MPRemoteCommandCenter or an equivalent to watchOS, and if the host app adds its own command handlers, disable the built-in WKAudioFileQueuePlayer behavior for previous-/next-track commands.

Data-transfer progress, speed

While some apps may be able to perform direct downloads of podcast episodes from the internet to the Watch, many will rely on transferring audio files from the iPhone to the Watch to ensure compatible formats, consistent timestamps, small files, or audio-processing features.

Transferring a podcast file to the Watch is a long-running task, often taking at least a few minutes per episode (and sometimes much longer), but the WCSessionFileTransfer class provides no progress information. So there’s no way for apps to inform users how long the transfers may take, or if they’re currently moving at all.

Minimum fix: Add a progress API on WCSessionFileTransfer .

Better fix: Add a progress API on WCSessionFileTransfer and provide actionable information if the transfer is currently paused or waiting for something, such as having other transfers ahead of it in a queue, or needing a different power or connectivity state.3

Additionally: Wi-Fi and LTE transfers to the Watch are currently much faster than Bluetooth, often by an order of magnitude, but the Watch seems to send all WCSessionFileTransfer data over Bluetooth even when connected to a power source. File transfers should use Wi-Fi when power allows.

Nice-to-have: Streaming audio playback

One of the most compelling features of the Series 3 Watch with LTE is streaming Apple Music playback, but there’s no streaming audio-playback API available to developers on watchOS today. Every method requires locally downloaded files.

I recognize this is a big task. That’s why it’s a “nice-to-have”.