Audio formats explained

There are many audio file formats available for distributing podcasts. The “MP3″ format is the most commonly used in the industry. The format is supported by nearly every portable media player, Internet connected TVs and most software-based media players.

We recommend MP3 format for the widest possible distribution

Below is a list of the most common audio formats with a brief description and note on usage. All of the following audio file formats offer high quality sound in a compressed format:

MP3 (MPEG Layer 3)

MP3 is the most widely supported audio format playable by most all portable audio players, Internet connected TVs, and software based media players. The format allows for special information to be stored in the audio file called id3 Tags. These special tags contain artist information, lyrics and album artwork. With the format being so widely accepted as well as robust enough to contain media information, it is the most ideal format to use in most all cases.

Patent holders declined to enforce license fees on free and open source MP3 decoders. Furthermore, individuals who use free and open source MP3 encoders are not required to pay patent fees.

File extensions: .mp3

Applications supported: Nearly all applications can play this format.

M4A / AAC (Advanced Audio Coding)

AAC format (M4A or ACC file extension) was designed to be the successor to the MP3 format and boasts a slightly smaller file size and better audio quality. The AAC format supports Digital Rights Management (DRM) and is more commonly found in use by iTunes for selling audio from the iTunes music store.

The AAC format is gaining momentum in adoption and might replace the MP3 format in the coming years. It is important to note that there are many devices that will not play M4A files, such as most Blackberry smartphones (only the latest Blackberry’s such as the 8100 “Pearl”, 9500 “Storm” and 8800 models support AAC) and car in-dash CD/MP3 players to name a few.

Even though the original file extension was .aac, .m4a is the more popular file extension for this audio format. In 2002, Apple started using the .m4a extension for audio distributed in its iTunes music store. Almost no one has used the .aac extension since. Apple also created file extensions for specific uses, such as .m4p for protected fair-play audio .m4b for audio books (bookmarkable audio) and .m4r for iPhone ring tones.

No patent licenses are required at this time to distribute media in the M4A/ACC format. M4a/AAC Patents have been filed by Apple Computer Inc.

File extensions: .m4a, .aac,  .mp4, .m4p, .m4r, 3gp

Applications supported: All Apple-based hardware, Android and most PC software.

Note: Quicktime or an iPod/iPad is required in order for audiobook chapter features to work.

Ogg (Vorbis)

Ogg Vorbis, not to be confused with the Ogg Theora video format, is an open source audio format maintained by Xiph.Org Foundation. Similar to the MP3 format, Vorbis allows for tags similar to ID3 called comments.

Ogg Vorbis is not a widely popular format and is not able to be played by most portable media players and Internet connected TVs.

The Ogg Vorbis format is unrestricted by software patents. As a result, the format is very popular among open source software developers and is commonly used in gaming applications.

The Ogg Vorbis format is embraced by the open source and Linux community. If you are creating content for this community, it is highly recommended that you distribute versions of your media in the Ogg format, in addition to MP3.

The Ogg Vorbis audio format is used in the new WebM video format and might become widely accepted by many video players and video playing software if adoption of the WebM is widespread.

File extensions: .ogg, .oga

Applications supported: Android, Firefox, Chrome and almost all Linux based software.

WMA (Windows Audio Media)

The WMA is a proprietary audio format developed by Microsoft. The WMA format can support Digital Rights Management (DRM). The WMA format is most commonly found in Microsoft products and select portable media players.

List of WMA supported devices

File extensions: .wma

Applications supported: Microsoft-based software and hardware

Other common formats that are not supported for podcasting

There are many more audio formats, including wave (.wav) and FLAC (.flac) that are not used for podcasting. These formats are considered “raw,” meaning they contain the original recording and are not compressed or optimized for the Web in any way. In most all cases a WAVE recording converted to an mp3 is ten times smaller in size, making the mp3 version the ideal choice for both bandwidth and speed of delivery.