Audio Codecs : Speech optimized codecs & Music optimized codecs

Now that you know how codecs work, it's time to see what codecs are available to podcasters, how they differ, and why you might want to use them. The first thing to consider is whether you're planning on using music in your podcast. If you are, then you definitely want to use a codec that is suited for music. If your podcast is just speech, then you may want to consider using a speech codec, because you'll be able to get very good quality at ridiculously low bit rates, thereby saving you money on bandwidth.

Choosing a codec is a tricky business. Newer codecs offer better quality, and some offer advanced functionality such as book marking and embedding images. However, many of the newer codecs play back only on a limited number of portable devices. If you want the latest and greatest features, but also want to cater to the widest possible audience, you may want to consider encoding to multiple formats.

Music-optimized codecs
As mentioned previously, if you're going to include any music at all in your podcast, you must use a music codec. Luckily, you're spoiled for choice. Here's a list of possible candidates:

MP3: The granddaddy of them all. MP3 wasn't initially designed as a low bit rate codec, so other codecs sound much better at low bit rates. It also does not support book marking. But just about every computer and portable media device in the world will play back an MP3 file.

Advanced Audio Coding (AAC): The new and improved MPEG audio codec, meant to replace MP3. The only problem is that it isn't supported on some portable players. AAC enables advanced features such as book marking and embedded images.

Windows Media Audio (WMA): The standard on Microsoft PCs. It has many advanced features such as markers, script commands, and embedded links. WMA is not supported on iPods, though it is supported on the "Plays for Sure" family of portable media devices.

RealAudio (RA): The default audio codec of the RealPlayer, which offers embedded links and script commands. It is supported on a number of cell phones.

OGG Vorbis: An open source audio codec offering excellent quality. Unfortunately, Vorbis isn't supported by many of the proprietary players, nor by the iPod.

Speech-optimized codecs
If your podcast doesn't include music, you should consider using a speech codec. They provide better quality at the same bit rate as a music codec, or the same quality at a reduced bit rate.

Audible Audio (AA): Developed for the first portable digital media player, which was released by Audible and designed to play back audio books. AA supports a number of advanced features such as book marking. Unfortunately, Audible doesn't make an AA encoder publicly available.

ACELP.net: The granddaddy of voice codecs. In fact, the AA format is based on the ACELP.net codec. ACELP.net is supported by both the Windows Media and Real players.

OGG Speex: Another branch of the OGG open source project, specializing in low bit rate speech compression.

Windows Media Audio Voice Codec: During Windows Media encoding you can specify that you're encoding voice content, and the Windows Media encoder will use a voiceoptimized codec.