The Be Book - Classes And Methods

Message Constants

The Media Kit has a number of message formats. The following table lists the messages (by their 'what' constants) and describes their intents. The subsequent sections list the fields that are contained in the messages.

Notification Messages

Declared in: media/MediaDefs.h

Messages with these 'what' are sent by the media server to any application that's registered to receive notifications by calling BMediaRoster::StartWatching().

Constant	Description
`B_MEDIA_WILDCARD`	Used to match any notification (used only in calls to `StartWatching()` and `StopWatching()`).
`B_MEDIA_NODE_CREATED`	A new node has been created
`B_MEDIA_NODE_DELETED`	A node has been deleted. (Not sent in R4.5.)
`B_MEDIA_CONNECTION_MADE`	Not sent in R4.5.
`B_MEDIA_CONNECTION_BROKEN`	Not sent in R4.5.
`B_MEDIA_BUFFER_CREATED`	Not sent in R4.5.
`B_MEDIA_BUFFER_DELETED`	Not sent in R4.5.
`B_MEDIA_FORMAT_CHANGED`	Not sent in R4.5.
`B_MEDIA_PARAMETER_CHANGED`	Indicates that a parameter in a `BParameterWeb` has changed.
`B_MEDIA_NEW_PARAMETER_VALUE`	Indicates that a parameter in a BParameterWeb has changed. Unlike the B_MEDIA_PARAMETER_CHANGED notification, this includes the new value.
`B_MEDIA_WEB_CHANGED`	Indicates that a node's `BParameterWeb` has changed.
`B_MEDIA_NODE_STOPPED`	Indicates that a node has stopped.
`B_MEDIA_FLAVORS_CHANGED`	Indicates that flavors have changed.
`B_MEDIA_DEFAULT_CHANGED`	Not sent in R4.5.
`B_MEDIA_TRANSPORT_STATE`	Not sent in R4.5.

B_MEDIA_WILDCARD

Purpose:	Constant only.
Source:	Your application.
Target:	The media server.
Hook:

When calling BMediaRoster::StartWatching() or BMediaRoster::StopWatching(), you can use this constant to match all media messages. This message has no actual format.

(No Be-defined fields)

B_MEDIA_NODE_CREATED, B_MEDIA_NODE_DELETED

Purpose:	Deliverable
Source:	The media server.
Target:	Target specified to `BMediaRoster::StartWatching()`.
Hook:

Sent to indicate that a node has been created or deleted in the media system.

Field	Type code	Description
`media_node_id`	`B_INT32_TYPE`	The ID of the media_node that was created or deleted.

B_MEDIA_CONNECTION_MADE, B_MEDIA_CONNECTION_BROKEN

Purpose:	Deliverable
Source:	The media server.
Target:	Target specified to `BMediaRoster::StartWatching()`.
Hook:	–

Sent to indicate that a connection between media nodes has been made or broken.

The B_MEDIA_CONNECTION_MADE message has three data fields:

Field	Type code	Description
`be:output`	`B_RAW_TYPE`	A media_output structure describing the connection's output.
`be:input`	`B_RAW_TYPE`	A media_input structure describing the connection's input.
`be:format`	`B_RAW_TYPE`	A media_format structure describing the format of the data that flows across the connection.

And B_MEDIA_CONNECTION_BROKEN has two.

Field	Type code	Description
`destination`	`B_RAW_TYPE`	A media_destination structure describing the destination of the connection that's been broken.
`source`	`B_RAW_TYPE`	A media_source structure describing the source of the connection that's been broken.

B_MEDIA_BUFFER_CREATED, B_MEDIA_BUFFER_DELETED

Purpose:	Deliverable
Source:	The media server.
Target:	Target specified to `BMediaRoster::StartWatching()`.
Hook:	–

Sent to indicate that a media buffer has been created or deleted.

B_MEDIA_BUFFER_CREATED's message has the following fields:

Field	Type code	Description
`clone_info`	`B_RAW_TYPE`	An area_info structure describing the buffer's location in memory. This is an array, one entry per buffer created.

B_MEDIA_BUFFER_DELETED looks like this:

Field	Type code	Description
`media_buffer_id`	`B_INT32_TYPE`	The buffer ID number of the buffer being deleted. This is an array, one entry per buffer deleted.

B_MEDIA_FORMAT_CHANGED

Purpose:	Deliverable
Source:	The media server.
Target:	Target specified to `BMediaRoster::StartWatching()`.
Hook:

Sent by the media server to indicate that the format used on a particular connection has changed.

Field	Type code	Description
`be:source`	`B_RAW_TYPE`	A media_source structure describing the source of the connection whose format changed.
`be:destination`	`B_RAW_TYPE`	A media_source structure describing the source of the connection whose format changed.
`be:format`	`B_RAW_TYPE`	A media_format structure describing the new format.

B_MEDIA_PARAMETER_CHANGED, B_MEDIA_NEW_PARAMETER_VALUE

Purpose:	Deliverable
Source:	The media server.
Target:	Target specified to `BMediaRoster::StartWatching()`.
Hook:

Sent by the media server to indicate that the value of a parameter has changed. B_MEDIA_PARAMETER_CHANGED only tells you which parameter changed (media_node and parameter ID). B_MEDIA_NEW_PARAMETER_VALUE also tells you which parameter changed, and what the new value is.

The B_MEDIA_PARAMETER_CHANGED message looks like this:

Field	Type code	Description
`be:node`	`B_RAW_TYPE`	A media_node structure indicating which node's parameter web has changed.
`be:parameter`	`B_INT32_TYPE`	The ID number of the parameter whose value has changed.

The B_MEDIA_NEW_PARAMETER_VALUE message is:

Field	Type code	Description
`node`	`B_RAW_TYPE`	A media_node structure indicating which node is reporting a changed parameter value.
`parameter`	`B_INT32_TYPE`	The parameter ID of the changed parameter.
`when`	`B_INT64_TYPE`	The performance time at which the change took effect. `value` `B_RAW_TYPE` The parameter's new value.

B_MEDIA_WEB_CHANGED

Purpose:	Deliverable
Source:	The media server.
Target:	Target specified to `BMediaRoster::StartWatching()`.
Hook:

Sent by the media server to indicate that a particular node's BParameterWeb has.

Field	Type code	Description
`node`	`B_RAW_TYPE`	A media_node structure indicating which node's parameter web has changed.

B_MEDIA_NODE_STOPPED

Purpose:	Deliverable
Source:	The media server.
Target:	Target specified to `BMediaRoster::StartWatching()`.
Hook:

Indicates that a media node has stopped.

B_MEDIA_FLAVORS_CHANGED

Purpose:	Deliverable
Source:	The media server.
Target:	Target specified to `BMediaRoster::StartWatching()`.
Hook:	–

Sent by the media server to indicate that the flavors supported by a particular add-on have changed.

Field	Type code	Description
`be:addon_id`	`B_INT32_TYPE`	The add-on ID of the add-on whose flavors have changed
`be:new_count`	`B_INT32_TYPE`	How many new flavors have been added.
`be:gone_count`	`B_INT32_TYPE`	How many flavors have been removed.