Standards:MUD Client Media Protocol

MUD Client Media Protocol (MCMP)

Status of this Memo

This memo describes the addition of a standardized namespace of the Generic Mud Communication Protocol (GMCP) telnet sub-negotiation protocol (201) that provides syntax and usage guidance for sending JSON formatted messages from game servers to text-based game clients to load, play and stop media files.

Overview and Rationale

With renewed interest in the MUD genre of gaming, expectations are high to provide sight and sound content that competes for audience with other gaming platforms. The purpose of the MUD Client Media Protocol (MCMP) is to establish a method of delivering media, such as game sounds, background music and video snippets, to text-based game clients via their widely accepted messaging platform, GMCP, which uses JSON as its data-interchange format. The intended return for introducing this protocol is to improve the MUD gaming experience and accessibility through standardized messaging between game servers and game clients. MUD Client Media Protocol (MCMP) is inspired by its predecessor Mud Sound Protocol (MSP).

Overview of the GMCP (201) Sub-negotiation Protocol

To recap, the GMCP protocol is a bidirectional telnet sub-negotiation protocol (See RFC 854) which fulfills the following conditions:

• GMCP is separated into several ‘namespaces’, which may be enabled or disabled by the client at any time. The ‘Core’ namespace is always enabled and may not be disabled. Namespaces should consist of case-insensitive alphabetical characters and stop characters (. - ASCII 46/0x2E), representable as [A-Za-z.].
• GMCP messages consist of the namespace and a command (case insensitive alpha characters) delineated by a stop character, and optionally a space character and JSON-encoded payload.
• GMCP messages may be sent by both the client or server at any time with no warning.

Update to namespace: Client.* for Client.Media

We are proposing an addition to the Client.* meta-namespace for Client.Media. This serves the purpose of reserving this namespace for handling game client media operations and supporting future expansion and integration.

Specification for Client.Media

The Client.Media family of GMCP packages provide a way for games to send sound, music and video events. GMCP media events are sent in one direction: from game server to to game client. Media files may be downloaded manually by the user and/or automatically via the game client. Game clients should advertise to servers that Client.Media is supported with a Core.Supports message from game client to server.

Core.Supports.Set ["Client.Media 1", ...]

Note: Presenting game sound and music media content is the current focus. Presenting video content was also successfully tested with this specification.

Commands - Server

Due to the limitations for legacy gaming platforms supporting all JSON data types, such as boolean (true and false), game clients should support parsing of values within the Client.Media namespace also as strings (surrounded by quotes).

Client.Media.Default

• Package: Client.Media.Default
• Purpose: Identify to the game client a default URL directory to load media files from an external resource.
• Guidance: For games that automatically download media files, perform a Client.Media GMCP event once upon player login.

Syntax:

Client.Media.Default {"url": "hxxps://www.example.com/media/"}

Usage:

Required	Key	Value	Purpose
Yes	"url"	<url>	Resource location where the media file may be downloaded.

Note: Some examples are shown here.

Note: Client.Media.Default was previous named Client.Media. Revised in February 2020 for GMCP specification conformance.

Client.Media.Load

• Package: Client.Media.Load
• Purpose: Load media files from an external source.
• Guidance: For games that automatically download media files and have the capability to cache with the game client.

Syntax:

Client.Media.Load {
  "name": "sword1.wav",
  "url": "hxxps://www.example.com/media/"
}

Usage:

Required	Key	Value	Purpose
Yes	"name"	<file name>	Name of the media file. May contain directory information (i.e. weather/lightning.wav).
Maybe	"url"	<url>	Resource location where the media file may be downloaded. Only required if a url was not set with Client.Media.Default.

Note: Some examples are shown here.

Client.Media.Play

• Package: Client.Media.Play
• Purpose: Play media files.
• Guidance: Game clients could choose whether to play only one media file at one time or multiple files at one time.

Syntax:

Client.Media.Play {
  "name": "city.mp3",
  "url": "hxxps://www.example.com/media/",
  "type": "music",
  "tag": "environment",
  "volume": 25,
  "loops": 3,
  "priority": 60,
  "continue": true,
  "key": "area-background-music",
}

Usage:

Required	Key	Value	Default	Purpose
Yes	"name"	<file name>		Name of the media file. May contain directory information (i.e. weather/lightning.wav).
Maybe	"url"	<url>		Resource location where the media file may be downloaded. Only required if the file is to be downloaded remotely and a url was not set above with Client.Media.Default or Client.Media.Load.
No	"type"	"sound", "music" or "video"	"sound"	Identifies the type of media.
No	"tag"	<tag>		Helps categorize media.
No	"volume"	1 to 100	50	Relative to the volume set on the player's client.
No	"loops"	-1, or >= 1	1	Number of iterations that the media plays. A value of -1 allows the sound or music to loop indefinitely.
No	"priority"	1 to 100		Halts the play of current or future played media files with a lower priority while this media plays.
No	"continue"	true or false	true	Only valid for media files with a "type" of "music". Continues playing matching new music files when true. Restarts matching new music files when false.
No	"key"	<key>		Uniquely identifies media files with a "key" that is bound to their "name" or "url". Halts the play of current media files with the same "key" that have a different "name" or "url" while this media plays.

Note: Some examples are shown here.

Client.Media.Stop

• Package: Client.Media.Stop
• Purpose: Stop playing media files.
• Guidance: An empty body will stop all media.

Syntax:

Client.Media.Stop {
  "name": "city.mp3",
  "type": "music",
  "tag": "environment",
  "priority": 60,
  "key": "area-background-music",
}

Usage:

Required	Key	Value	Purpose
No	"name"	<file name>	Stops playing media by name matching the value specified.
No	"type"	"sound", "music" or "video"	Stops playing media by type matching the value specified.
No	"tag"	<tag>	Stops playing media by tag matching the value specified.
No	"priority"	1 to 100	Stops playing media with priority less than or equal to the value.
No	"key"	<key>	Stops playing media by key matching the value specified.

Note: Some examples are shown here.

Authors

• Mike Conley (Tamarindo, Co-Administrator at StickMUD and Mudlet contributor) sousesider[at]gmail.com
• Eric Oestrich (Developer of ExVenture and Grapevine) eric[at]oestrich.org

Notes

• Known clients implementing this specification:
  • Mudlet version 4.4+. See documentation.