What format/bitrate are iTunes sample files on the iTunes store?
AAC format at 256 kbit/s, m4a

Originally, songs were encoded using FairPlay-encrypted 128 kbit/s AAC streams in an mp4 wrapper, using the .m4p extension.

From May 29, 2007, tracks on the EMI label were made available in a DRM-less format called iTunes Plus. These files are unprotected and are encoded in the AAC format at 256 kbit/s, twice the bitrate of standard tracks bought through the service. They are labelled as "purchased AAC audio file" (.m4a) rather than "protected AAC audio file" (.m4p) in iTunes.

in January 2009, Apple announced that all music would be available in the iTunes Plus format, bringing an end to the sale of music with DRM on iTunes. In April 2009, the sale of protected music ended in western versions of the store, making all music in the iTunes Store "iTunes Plus." iTunes Store users may choose to "upgrade" any of their downloaded iTunes music to iTunes Plus if they wish, but most songs require payment to do so. FairPlay DRM-protected music was still available in the Japanese iTunes store, up until February 22, 2012, when they upgraded to the iTunes Plus model.[105]

In September 2009, Apple introduced the iTunes LP format (known pre-launch by the code name "Cocktail")[106] which features visual, interactive content alongside album tracks and lyrics.