A good podcast is meant to immerse the listener in the story, and maintain their interest even when there are no visuals involved, through powerful interviews and narration, an interesting topic and riveting audio. Yet some podcasts – most notably Serial's popular investigative series, S-Town – do that so well that people feel compelled to look for images or additional information as they listen in order to get even closer to the story.

Last month, The Guardian Mobile Innovation Lab launched a new experimental audio player for mobile web browsers, to look at how listening to podcasts outside of smartphone apps could open up the format to people who are not necessarily podcast aficionados.

The team also wanted to figure out how the listening experience could be elevated through the use of visuals and notifications, so they launched the player with a new audio series called Strange Bird. Hosted by Guardian US data editor Mona Chalabi, the podcast uses data and statistics to address common topics, such as miscarriages.

"Questions of data aside, some of the research shows that a lot of the [podcast] consumption is within apps and that works counter to the logic of news organisations producing their own apps for their own audiences," Sasha Koren, the Lab's editor, told Journalism.co.uk in a recent podcast.

"Not to say that one has to overtake the other, but with a podcast in a web player you can appeal to your whole audience regardless of their mobile device or whether they habitually listen to podcasts. You have access to the broad range of people who are already coming to read your content so that opens up the possibility for people who might not seek out a podcast or know they're even available, to subscribe."

When people listen to Strange Bird in their mobile browsers, they will periodically receive links, graphs or images to complement the audio as the episode progresses. For example when Chalabi talks to her mother in the opening of the first episode, or when she mentions a specific set of data related to miscarriage, a picture and a data visualisation respectively will pop up in the player. If the user taps a link with additional context to the story, the link will open in a new tab on their device, without disrupting the audio.

Listeners using Chrome browsers on their Android devices can also opt in to receive notifications when a new visual is sent, and they can also subscribe to new episodes through the player, although the two features aren't yet available to iOS users.

Alastair Coote, formerly the Lab's developer, said the team initially struggled with the best way to design the player, since the concept was inspired by some APIs that Chrome provided for audio players in browsers, but they decided on a chat interface because it was something people were already familiar with, and it also matched the chatty and informal tone of the podcast.

They also wanted the experience to feel optional and not make it seem like listeners were "doing something wrong" if they chose to focus solely on the audio and not interact with any of the additional elements. Striking the right balance between the flow of information and the audio was also an important consideration.

"We had a conversation where we had all listened to S-Town and we all wanted to know where the rose garden was, or to put in the GPS coordinates that were mentioned, so it struck us there was an opportunity to see if we could make it a little bit easier for people to find that information within mobile. But we also realised that some people listen to podcasts for a pure audio experience and that they may not be interested," Koren said.

"We did look at the cadence of what we were sending to people. When you're sending people information, you set up this expectation that it's going to come fairly regularly so if you have a long gap where someone is talking but you're not actually augmenting that with a visual, that can feel a bit weird.

"In the same way a text editor might edit a story and think about where there's a hole, or how the flow of information is building or holding together, we realised not only did we have to think about that in terms of the script but we had to think about that in terms of the visuals and information we were sending, so it's a very different way of approaching storytelling."

Earlier in the development process of the player, staff members at the Lab analysed a handful of podcasts, including the Guardian's Football Weekly and NPR's Hidden Brain, for their potential to work with a format where visuals or other elements could be sent to people.

While this interactive format might not fit every podcast, the goal is to give news organisations and podcast producers an idea of what's possible with audio on the mobile web once consumption and discovery "don't go through someone else's app".

"The audio definitely did come first in this scenario (...) and we didn't necessarily think that Strange Bird could be consumed only in the player," Koren said.

"There is a scenario where we could make something intended just for the player, but as a first step we wanted to find out where the opportunity is for people to engage with podcasts and where they would actually prefer to just have the audio by itself.

"The fact that you can do either and have a beautiful experience worked out very well. We wanted to make something that didn't feel disparate and disconnected from the audio as an experience."

Listen to the podcast with Koren and Coote here.

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