.frob (FroB) File Format 💖

1. Summary

The FroB format is a simple, binary event stream designed for mono frequency playback. It is a compact, special-purpose format intended for the frobplayer app to play music on a PC's motherboard beeper.

All FroB-compliant files should have an extension of ".frob", with a magic value of "FROB1337" in the file's header.

2. File Structure

A FroB file is composed of three parts, in order:

• Header
• Event Stream (N * 8 bytes): A stream of playback events.
• End-of-Stream (EoS) Marker (8 bytes): An event that signals an end to playback.

All multi-byte values are encoded in LE.

2.1. Header

A FroB file should have FROB1337 encoded with ASCII in 8 bytes.

This allows the player to validate the file and prevent attempts to play non-FroB files.

2.2. Events

An event is 8 bytes, split into 2 uint32 values.

The first 4 bytes are the delta time. This is the time to wait before executing the event in microseconds. The second 4 bytes is the frequency to play, in hertz.

If an event's Frequency is "0", the player will stop playing all tones.

2.3. End-of-Stream (EoS) Marker

This has the same structure as an Event (see 2.2, Events), with special values:

• Delta Time: Any value, but full compliance to the FroB specification requires 0.
• Frequency: 0xFFFFFFFF

This signals a valid end to playback. A player should stop playback upon reading this event. This helps the player distinguish a complete file from one that's corrupted.