Storage media

Digital audio formats can be stored on any digital storage media. The first mass-market digital audio format was the audio CD, which standardized a storage media as well as a digital audio encoding format. The encoding format (uncompressed WAV files sampled at 44.1KHz) was also used to store digital audio on other devices, but other encoding formats were also developed.

Digital storage media includes

The flash media has continued to gain in capacity and speed, and shrink in size and cost, so is taking over much of the digital data storage market. Because of that trend, and the far smaller interfaces required to read flash media compared to CDs, it is even taking over the digital audio storage market, and newer vehicles do not reserve space for CD players, but rather have SD card or USB interfaces for user digital audio, and generally also Bluetooth interfaces so audio can be played from smartphones.

Audio formats

There are many different audio formats. For details on most of them, see this Wikipedia article. Uncompressed formats include WAV and AIFF. Compressed formats come in two flavors: lossless and lossy. The article discusses all three kinds. Some formats are were created by particular manufacturers, others via standards bodies.

By far, the most universally supported formats are CD audio (lossless and uncompressed) and MP3 (using parameterized lossy compression). While other formats may be "default" or "preferred" on different systems, and by different people, and some media players can play quite a variety of different formats, every modern (and many obsolete) computer, smartphone, automobile digital audio interface, and standalone player I've ever heard of supports at least one of these formats.

Among CD players, there are three varieties: CD audio only, CD audio + MP3, and CD audio + MP3 + some number of other formats.

Among standalone digital players, there are two varieties of modern interest: MP3 only, and MP3 + some number of other formats.

An MP3 file compressed to 128Kbps bitrate (the bitrate is the primary control over the compression factor) is indistinguishable to most people from the uncompressed audio, and about one-tenth the size. This is the format I use for compressed audio files.