The loosely defined category of S1 MP3 players is comprised by a large amount of then-inexpensive handheld digital audio players. The players were mainly widespread around 2005–2006 but the series continued for years afterwards, blurring into that of so-called "MP4 players" employing S1 and competing architectures. Despite being primarily defined by the use of a system-on-a-chip of one of the Actions brands usually of the ATJ20xx series and some common core features, S1 products vary widely in software and hardware as well as design (including lookalikes and even counterfeits of other players), leading to a jumble of hard to identify internal designs, all employing non-mutually-interchangeable firmwares.

Capabilities

Some models have additional features, such as:

Software utilities

Available utilities for Microsoft Windows include an ACT to WAV file converter (for files recorded on the device), a basic desktop editor to enter contact details for the device's phone book function and device drivers for Windows 98. An 8 cm CD-ROM containing some or all of these is included with some versions of the device. There are also tools developed by individuals under the Open-Source license, such as s1res ans s1clone that allow the consumer to modify its device by changing bitmaps and text. By using decompilers, it is possible to add and replace features of the device, steps that were described on the s1mp3.org wiki page.

Firmware update issues

The firmware used in various S1 MP3 players differs significantly, but this is not widely understood. Problems have arisen as consumers have attempted to upgrade their players using incompatible firmware with a higher version number. This can damage the players almost permanently. However, a 'dead' player can sometimes be recovered by opening it, shorting some pins and uploading a full firmware from the PC. Guides on recovering the players were available on a unofficial website s1mp3.org that is offline since 2019.

Example models and brands

''The following are brand names in alphabetical order. Due to common mold specifications of the player type, this list will never be complete.'' There are also several models which carry no brand name or model number on the device or packaging, and a few sold under counterfeit trademarks such as Sony, Samsung, iPod, and others that use the same spelling in their brand name yet different brand styling, with inverse effect to established brands that offer similar or unrelated products.