Back in the mid-2000's there was a buzz about a new technology threatening radio. It was called podcasting (a mash up of the words "iPod" and "broadcasting"). The way it worked back then was a person took an iPod (or similar device) and attached it to their home computer. They would subscribe to podcasts being made available from many sources on the Internet. The device would stay attached overnight with the computer running. The next morning the listener would unplug the fully charged device. Any of the podcasts with new content would be automatically updated. Any that had been listened to in previous days would be automatically deleted. A listener really wasn't restricted to overnight, but there was a requirement for the device to be hooked up with a cable for a length of time to allow the automated downloading and updating of content. The idea was popular among some circles, but usage remained fairly low. The dedicated device seemed more popular for music than for refreshed podcast content.
Then came the rise of the smart phone. Podcast software has been made commonly available on new phones. One difference between the iPod model and the smart phone model is availability of bandwidth. Cell phone bandwidth and WiFi signal coverage has been steadily rising and costs continue to come down. Smart phones are so prevalent now that I've seen reports suggesting that in North America there are more smart phones in use than there are people. With the growth of bandwidth, for a person to get access to a podcast there is no longer a need to hook up a cable and wait. The delivery can come to the phone through the same data paths used for talk, text, email and web surfing. By using the smart phone for podcast content, listeners only have to carry one device. Before they would carry a phone for talk and text, and separately they would carry an iPod (or other audio device) for music and podcast content. The dedicated media player has not disappeared, but with the rise of the integrated smart phone device they are clearly less popular than they once were. Just stroll down the technology aisle at your local store and check out the ratio of smart phones to pocket-sized dedicated media players.
Interestingly, the title of "podcast" has not changed even though those using an actual iPod to play the content are probably small in number. Even when the original model was first in vogue there were other devices (not just iPods) that could download and play the content. Apple did a good job out-marketing the competing media players and the name stuck.
Recently a number of organizations have gone down the path of creating podcasts again. I assume this rise of podcast content is associated with the ubiquity of smart phones. Two of the leading recent examples are Serial, produced by This American Life, and Invisibilia, Produced by NPR. Both of these shows have had downloads numbering in the millions. The recent popularity of podcasts has been so good that it is beginning to get the attention of sponsors. Ads are often embedded in the content.
There is some cross over between media delivery methods. For example more than 200 NPR stations have run Invisibilia content on the broadcast radio air. This American Life agreed to dedicate one of its regular weekly radio broadcast programs to Invisibilia content.
The effect of the rebirth of podcasts remains to be seen. There are many audio podcast content sites springing up all over the Internet. All reports I've seen show radio listenership on the decline while podcast listenership is on the rise. That said, the scales of these two media mechanisms are degrees of magnitude different. Radio listenership is many times higher than podcast listenership right now.
The measurements are not apples-to-apples. Radio listeners are measured in cume (cumulative audience, total number of listeners) and AQH (average quarter-hour, the longer people listen the higher the AQH). Similar to television, if a radio is on there is no way to know how many people are listening. For example, how many people are in the car while the radio is on and are they actually listening? If the family is running errands, several may have headphones on, listening to MP4's in the back seat for example. The numbers are also extrapolated from sampled listeners through polling services such as Arbitron.
Podcasts are measured in number of downloads. Downloading a program is not the same as actually listening to the program. For example if a person downloads the Serial series, but only listens to the first program all the episodes count in the statistics.
Regardless of any statistical errors in counting, what is important is trending. Any statistician will tell you that so long as something is measured in the same way consistently then any error is also consistent. That means the trends will be valid even if the data is slightly off.
One last difference to mention about podcasts. Since these are recorded files shared on the Internet, they are not broadcast over the airwaves. This means that podcasts are not subject to the same rules that content shared over the air is subject to. In the United States, broadcast content is regulated by the Federal Communications Commission (FCC). I have not seen any sort of rating system for podcast content. It's not required that the content producer offer warnings about the nature of the content, though many do. Rough language and sensitive topics are not unusual in this arena. Much content may be created by people who do not follow journalistic ethical standards. Like much on the Internet, fact checking may be lacking. Some might argue that such standards are not followed on broadcast media either, but at least it is supposed to be. No such restriction exists for podcasts.
As I have experimented with podcasting I find an interesting dilemma. The podcast listening has begun to compete with audio books and radio for my commute and workout listening. I've become a microcosm of the phenomenon of media splintering.