Regarding AAC:
"Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at many bit-rates.
"AAC’s best known use is as the default audio format of Apple’s iPhone, iPod, iTunes, and the format used for all iTunes Store audio (with extensions for proprietary digital rights management).
"AAC is also the standard audio format for Sony’s PlayStation 3, Nintendo’s Wii (with the Photo Channel 1.1 update installed for Wii consoles purchased before late 2007) and the MPEG-4 video standard. HE-AAC is part of digital radio standards like DAB+ and Digital Radio Mondiale.
"It is specified both as Part 7 of the MPEG-2 standard, and Part 3 of the MPEG-4 standard. As such, it can be referred to as MPEG-2 Part 7 and MPEG-4 Part 3 depending on its implementation, however it is most often referred to as MPEG-4 AAC, or AAC for short…
"No licenses or payments are required to be able to stream or distribute content in AAC format. [8] This reason alone makes AAC a much more attractive format to distribute content than MP3, particularly for streaming content (such as Internet radio).
"However, a patent license is required for all manufacturers or developers of AAC codecs, that require encoding or decoding.[9] It is for this reason FOSS implementations such as FAAC and FAAD are distributed in source form only, in order to avoid patent infringement.
“AAC uses proprietary technology, and thus requires a patent license. Contrary to popular belief, it is not the property of a single company, having been developed in a standards-making organization.”