BMediaRoster¶

Constructor and Destructor¶

BMediaRoster()

BMediaRoster::BMediaRoster()

You never construct a BMediaRoster yourself. Instead, use the static Roster() function to obtain an instance of the BMediaRoster class that you can use.

~BMediaRoster()

virtual BMediaRoster::~BMediaRoster()

You never delete a BMediaRoster yourself. Just let it go away automatically when your application shuts down.

Member Functions¶

AudioBufferSizeFor()

ssize_t BMediaRoster::AudioBufferSizeFor(int32 channelCount, uint32 sampleFormat, float frameRate, bus_type busKind)

AudioBufferSizeFor() returns the size, in bytes, that the Media Kit recommends for audio data with channelCount channels, with the specified sampleFormat and frameRate.

The busKind argument is a bus_type value (see drivers/config_manager.h) indicating the type of bus the data is moving across. Specify B_UNKNOWN_BUS if you don’t know.

Connect(), Disconnect()

status_t BMediaRoster::Connect(const media_source &source, const media_destination &destination, media_format *ioFormat, media_output *outOutput, media_input *outInput)
status_t BMediaRoster::Connect(const media_source &source, const media_destination &destination, media_format *ioFormat, media_output *outOutput, media_input *outInput, uint32 inFlags, void *_reserved = NULL)

status_t BMediaRoster::Disconnect(media_node_id sourceNode, const media_source &source, media_node_id destinationNode, const media_destination &destination)

Connect() negotiates a connection from the source to the destination, using the media format specified in ioFormat as a basis for the negotiation; ioFormat is changed to the negotiated format before this call returns. This describes the format of media data that will flow across the connection.

The actual connection is returned as an output and an input in outOutput and outInput. These two structures contain the data format as interpreted by the source and destination. There may be differences among these formats if wildcard fields were used in the original format.

The second form of Connect() lets you specify connect flags. Currently the only possible flag is B_CONNECT_MUTED, which indicates that the connection should be muted on creation.

The actual media_source and media_destination used for the connection may vary from those passed into Connect() if the source or the destination creates new sources or destinations for each connection request; the outOutput and outInput structures contain the actual media_source and media_destination values resulting from the call.

For more detailed information on the use of wildcards in format negotiation, see media_audio_format::wildcard and media_video_format::wildcard. A media_format with a type of B_MEDIA_UNKNOWN_TYPE matches any media class and format, although without specific knowledge of the source and destination, this will rarely result in a useful connection.

Disconnect() breaks the connection established between source and destination, which must belong to the nodes sourceNode and destinationNode, repectively.

The result of breaking a connection that’s currently running is undefined, but is not permitted to crash. Your application should stop both nodes involved in a connection prior to disconnecting them.

Note

These functions will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error terminating the connection.
`B_NAME_NOT_FOUND`	The connection couldn’t be made.
Other errors.	The nodes that are being connected may return other error codes as they see fit.

GetAllInputsFor(), GetAllOutputsFor()

status_t BMediaRoster::GetAllInputsFor(const media_node &node, media_input *outInputs, int32 bufNumInputs, int32 *outTotalCount)

status_t BMediaRoster::GetAllOutputsFor(const media_node &node, media_output *outOutputs, int32 bufNumOutputs, int32 *outTotalCount)

GetAllInputsFor() fills the array of media_input structures specified by outInputs with information about all inputs belonging to node; the number of elements that outInputs can hold is passed in bufNumInputs.

Similarly, GetAllOutputsFor() fills the array outOutputs with information about all outputs from the specified node.

Both functions return the number of elements actually returned in the buffer in outTotalCount. If this number is less than the number you requested, your buffer was too small to receive all the results of the query. In this case, you might want to resize your array and try again.

Note

These functions will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error.
`B_MEDIA_BAD_NODE`	The node isn’t of the correct type for the call you issued.
Other errors.	An error occurred communicating with the producer or with the Media Server.

GetAudioInput(), GetVideoInput()

status_t BMediaRoster::GetAudioInput(media_node *outNode)

status_t BMediaRoster::GetVideoInput(media_node *outNode)

These functions return the nodes designated by the user as the preferred nodes for audio and video input. You can then query the returned node, hook into it, and manipulate it, using the reference returned in outNode.

Once your application has finished using these nodes (and they’ve been stopped and disconnected), you should release them by calling ReleaseNode().

Return Code	Description
`B_OK`	No error locating the default input node.
`B_NAME_NOT_FOUND`	The default node couldn’t be identified.

GetAudioOutput(), GetVideoOutput(), GetAudioMixer()

status_t BMediaRoster::GetAudioOutput(media_node *outNode)
status_t BMediaRoster::GetAudioOutput(media_node *outNode, int32 *outInputID, BString *outInputName)

status_t BMediaRoster::GetVideoOutput(media_node *outNode)

status_t BMediaRoster::GetAudioMixer(media_node *outNode)

These functions return the nodes designated by the user as the preferred nodes for audio and video output. You can then query the returned node, hook into it, and manipulate it, using the reference returned in outNode.

The second form of GetAudioOutput() returns additional information, including the input ID of the input used for audio output, and the input’s name.

You should usually use GetAudioMixer() when getting a node for playing audio instead of using the GetAudioOutput() function. GetAudioOutput() returns the lower-level node for audio output, which you would typically only need access to if you wanted to do some form of processing on all audio data being played in the system (such as a level meter).

The GetAudioMixer() function returns a reference to the audio mixer, which will perform audio mixing, format conversion, and sample rate conversion for you, then pass along the audio to the output node.

Once your application has finished using these nodes (and they’ve been stopped and disconnected), you should release them by calling ReleaseNode().

Return Code	Description
`B_OK`	No error locating the default input node.
`B_NAME_NOT_FOUND`	The default node couldn’t be identified.

GetConnectedInputsFor(), GetFreeInputsFor()

status_t BMediaRoster::GetConnectedInputsFor(const media_node &node, media_input *outActiveInputsList, int32 numListInputs, int32 *outNumInputs)

status_t BMediaRoster::GetFreeInputsFor(const media_node &node, media_input *outFreeInputsList, int32 numListInputs, int32 *outNumInputs, media_type filterType = B_MEDIA_UNKNOWN_TYPE)

GetConnectedInputsFor() fills the array of media_input structures specified by outActiveInputsList with information about all inputs belonging to node that are currently connected to some output; the number of elements that outActiveInputsList can hold is passed in numListInputs.

Similarly, GetFreeInputsFor() fills the array outFreeInputsList with information about all inputs that are still available in the specified node. Specifying a filterType other than B_MEDIA_NO_TYPE lets you obtain a list of inputs for a specific media type (or for inputs that can handle any media type). This is especially useful if you’re only interested in a list of accepted media types your application supports.

Note

Even though a node may report that a specific number of free inputs are available, it is possible that a node might create more inputs on demand. There is no way to know if this might happen, so GetFreeInputsFor() may not tell you whether or not a node can accept all the connections you’d like to make.

Both functions return the number of elements actually returned in the buffer in outNumInputs. If this number is less than numListInputs, your buffer was too small to receive all the results of the query. In this case, you might want to resize your array and try again.

These functions will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error cloning the node.
`B_NAME_NOT_FOUND`	The requested node couldn’t be cloned.

GetConnectedOutputsFor(), GetFreeOutputsFor()

status_t BMediaRoster::GetConnectedOutputsFor(const media_node &node, media_output *outActiveOutputsList, int32 numListOutputs, int32 *outNumOutputs)

status_t BMediaRoster::GetFreeOutputsFor(const media_node &node, media_output *outFreeOutputsList, int32 numListOutputs, int32 *outNumOutputs, media_type filterType = B_MEDIA_UNKNOWN_TYPE)

GetConnectedOutputsFor() fills the array of media_output structures specified by outActiveOutputsList with information about all outputs belonging to node that are currently connected to some input; the number of elements that outActiveOutputsList can hold is passed in numListOutputs.

Similarly, GetFreeOutputsFor() fills the array outFreeOutputsList with information about all outputs that are still available in the specified node. Specifying a filterType other than B_MEDIA_UNKNOWN_TYPE lets you obtain a list of outputs for a specific media type (or for outputs that can handle any media type). This is especially useful if you’re only interested in a list of accepted media types your application supports.

Note

Even though a node may report that a specific number of free outputs are available, it is possible that a node might create more outputs on demand. There is no way to know if this might happen, so GetFreeOutputsFor() may not tell you whether or not a node can accept all the connections you’d like to make.

Both functions return the number of elements actually returned in the buffer in outNumOutputs. If this number is less than numListOutputs, your buffer was too small to receive all the results of the query. In this case, you might want to resize your array and try again.

Note

These functions will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error.
`B_MEDIA_BAD_NODE`	The node isn’t a buffer producer.
Other errors.	An error occurred communicating with the producer or with the Media Server.

GetDormantFlavorInfoFor()

status_t BMediaRoster::GetDormantFlavorInfoFor(const dormant_node_info &inDormantNode, dormant_flavor_info *outFlavor)

This function returns, in outFlavor, information describing the dormant flavors supported by the dormant node inDormantNode.

Return Code	Description
`B_OK`	No error.
Messaging errors.	An error occurred communicating with the Media Server.

GetDormantNodes()

status_t BMediaRoster::GetDormantNodes(dormant_node_info *outDormantNodeList, int32 *inOutNumNodes, const media_format *hasInputFormat = NULL, const media_format *hasOutputFormat = NULL, char *name = NULL, uint64 requireKinds = 0, uint64 denyKinds = 0)

Queries dormant nodes (those nodes that live in add-ons, rather than in the application) and returns those who match the specified inputs. If hasInputFormat isn’t NULL, the node has to be a BBufferConsumer and have an input format compatible with the format described in hasInputFormat. Likewise, if hasOutputFormat isn’t NULL, the node has to be a BBufferProducer that’s compatible with the format described in hasOutputFormat.

If name isn’t NULL, the node has to have a name that equals name, or, if the last character of name is an asterisk (“*”), a name whose initial characters match name up to, but not including, the asterisk.

The requireKinds and denyKinds arguments specifiy, respectively, the kinds that must be supported, and the kinds that must not be supported by the returned nodes.

Matching nodes are returned in outDormantNodeList. You should pass the size of the outDormantNodeList array (the number of elements that the array can hold) in inOutNumNodes; when this function returns, the value in inOutNumNodes will be changed to the actual number of matching nodes found, unless an error occurs.

Nodes you obtain using GetDormantNodes() must be released when you’re done using them. To do this, be sure they’re stopped and disconnected, then call ReleaseNode().

Return Code	Description
`B_OK`	No error cloning the node.
`B_NAME_NOT_FOUND`	The requested node couldn’t be cloned.

GetFileFormatsFor()

status_t BMediaRoster::GetFileFormatsFor(const media_node &fileInterface, media_file_format *outFormatList, int32 *inOutFormatCount = 0)

Given a BFileInterface node in fileInterface, returns information about the file formats the file interface can deal with in the array outFormatList. On entry, inOutFormatCount points to the number of media_file_format structures that can fit in the array specified by outFormatList. Upon return, it will contain the actual number of formats returned, unless GetFileFormatsFor() returns an error.

Note

This function will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error sending the set mode request.
`B_NAME_NOT_FOUND`	The requested node couldn’t be cloned.

GetFormatFor()

status_t BMediaRoster::GetFormatFor(const media_output &output, media_format *ioFormat, uint32 flags = 0)
status_t BMediaRoster::GetFormatFor(const media_input &input, media_format *ioFormat, uint32 flags = 0)
status_t BMediaRoster::GetFormatFor(const media_node &input, media_format *ioFormat, float quality = B_MEDIA_ANY_QUALITY)

GetFormatFor() returns the media_format being used by the given object, which may be a media_output, a media_input, or a media_node. Pass in ioFormat a pointer to a media_format object to be filled out with the object’s format.

The flags currently must be zero.

Return Code	Description
`B_OK`	No error.
`B_BAD_VALUE`	You can’t pass NULL for ioFormat.
`B_MEDIA_BAD_NODE`	The node isn’t of the correct type for the given request.
`B_MEDIA_BAD_SOURCE`	The node’s `media_source` is invalid.
Messaging errors.	An error occurred communicating with the Media Server.

GetInitialLatencyFor()

status_t BMediaRoster::GetInitialLatencyFor(media_node &producer, bigtime_t *outLatency, uint32 *outFlags = NULL)

Returns, in outLatency, the additional amount of time in microseconds the specified producer node requires in order to synchronize to a signal. For example, a TV capture card that’s started while the capture is in the middle of a field will have to wait until the next field begins before actually starting to produce buffers.

outFlags is set to the flags returned by the producer. Currently there aren’t any flags defined, so this will be returned as zero for now.

Return Code	Description
`B_OK`	No error.
`B_BAD_VALUE`	outLatency was specified as NULL.
`B_MEDIA_BAD_NODE`	producer isn’t a valid node.
Port errors.	An error occurred communicating with the producer.

GetInstancesFor()

status_t BMediaRoster::GetInstancesFor(media_addon_id addon, int32 flavor, media_node_id *outID, int32 *ioCount = 0)

Given the specified addon ID and flavor, this function fills the outID list with up to ioCount node IDs that were derived from the specified add-on. If you specify zero for ioCount, one node ID will be returned. On return, ioCount is changed to indicate how many nodes have been returned in the list.

Return Code	Description
`B_OK`	No error.
Port errors.	Communication with the Media Server failed.

GetLatencyFor()

status_t BMediaRoster::GetLatencyFor(const media_node &producer, bigtime_t *outLatency)

Reports in outLatency the maximum latency found downstream from the specified BBufferProducer, producer, given the current connections.

If an error occurs, the value in outLatency is unreliable.

Note

This function will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error.
Other errors.	Unable to get the latency.

GetLiveNodes()

status_t BMediaRoster::GetLiveNodes(live_node_info *outLiveNodeList, int32 *ioTotalCount, const media_format *hasInput = NULL, const media_format *hasOutput = NULL, const char *name = NULL, uint64 nodeKinds = 0)

Queries the Media Server for a list of all currently active nodes (whether they’re running or not), and fills the array specified by outLiveNodeList with information about the nodes. The size of the array should be specified—in terms of how many elements it can contain—by the ioTotalCount argument; the actual number of entries in the returned list will be stored in ioTotalCount before the call returns.

An active node is a node that is preloaded by the system and is always available for use, as opposed to a dormant node, which resides in an add-on and is only loaded when instantiated using InstantiateDormantNode().

You can obtain a more specific result list by specifying one or more of the hasInput, hasOutput, name, and nodeKinds arguments. hasInput and hasOutput let you restrict the resulting list to containing nodes that accept as input (or output) the specified format.

You should always specify 0 for nodeKinds; this parameter is currently not used.

Return Code	Description
`B_OK`	No error.
Other errors.	Unable to get the list of live nodes.

GetNodeAttributesFor()

ssize_t BMediaRoster::GetNodeAttributesFor(const media_node &node, media_node_attributes *outArray, size_t inMaxCount)

Fills the array outArray with up to inMaxCount attributes of the given node. Returns the number of attributes returned. If the result is less than zero, an error occurred.

GetNodeFor()

status_t BMediaRoster::GetNodeFor(media_node_id nodeID, media_node *clonedNode)

Given a node specified by node_id, GetNodeFor() returns in clonedNode a media_node reference to a clone of the node. You can then use the clonedNode to query the node for available inputs, outputs, and so forth.

Once your application has finished using the returned node (and it’s been stopped and disconnected), you should release it by calling ReleaseNode().

Return Code	Description
`B_OK`	No error cloning the node.
BMessageerrors.	Unable to get the list of live nodes.

GetParameterWebFor()

status_t BMediaRoster::GetParameterWebFor(const media_node &node, BParameterWeb **outWeb)

Instantiates a BParameterWeb that describes the internal layout of a specific controllable node and stores a pointer to the BParameterWeb in outWeb. You can then walk the various BParameters within the web to figure out what there is to control, and to present a user interface to the node’s parameters. Delete the web pointed to by outWeb when you’re done with it.

Note that the StartControlPanel() function provides an easy, painless way to automatically present user interface for configuring nodes.

Note

This function will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error obtaining the `BParameterWeb`.
`B_MEDIA_BAD_NODE`	The requested node is invalid.

GetReadFileFormatList(), GetWriteFileFormatList()

status_t BMediaRoster::GetReadFileFormatList(const dormant_node_info &inNode, media_file_format *outReadFormats, int32 inReadCount, int32 *outReadCount)

status_t BMediaRoster::GetWriteFileFormatList(const dormant_node_info &inNode, media_file_format *outWriteFormats, int32 inWriteCount, int32 *outWriteCount)

These two functions return lists of file formats that the dormant node described by inNode can read or write.

GetReadFileFormatList() returns in the array specified by outReadFormats a list of file formats the node can read. Specify in inReadCount the number of formats that can be held by the outReadFormats array. On exit, outReadCount indicates how many formats are being returned in the array.

GetWriteFileFormatList() returns in the array specified by outWriteFormats a list of file formats the node can write. Specify in inWriteCount the number of formats that can be held by the outWriteFormats array. On exit, outWriteCount indicates how many formats are being returned in the array.

Return Code	Description
`B_OK`	The list was returned without error.
`B_BAD_VALUE`	outReadFormats or outWriteFormats is NULL.
BMessageerrors.	An error occurred communicating with the Media Server.

GetRealtimeFlags(), SetRealtimeFlags()

status_t BMediaRoster::GetRealtimeFlags(uint32 *outEnabled)

status_t BMediaRoster::SetRealtimeFlags(uint32 inEnabled)

GetRealtimeFlags() returns flags that the Media Server uses to determine whether or not memory needs to be locked down. SetRealtimeFlags() sets these flags, and is generally only called by the Media preference application.

Any or all of these flags can be set, in combination.

Constant	Description
`B_MEDIA_REALTIME_ALLOCATOR`	When set, `rtm_alloc()` will return locked memory.
`B_MEDIA_REALTIME_AUDIO`	Audio add-ons in the Media Server are locked in memory, and should lock their thread stacks using `media_realtime_init_thread()`.
`B_MEDIA_REALTIME_VIDEO`	Video add-ons are locked in memory, and should lock their thread stacks using `media_realtime_init_thread()`.
`B_MEDIA_REALTIME_ANYKIND`	All Media add-ons are locked in memory, and should lock their thread stacks using `media_realtime_init_thread()`.

See the BMediaNode overview for a discussion of realtime allocation and thread stack locking.

Return Code	Description
`B_OK`	No error.
Other errors.	Unable to set or retrieve the realtime flags.

GetStartLatencyFor()

status_t BMediaRoster::GetStartLatencyFor(const media_node &timeSource, bigtime_t *outLatency)

Reports in outLatency the maximum latency found downstream from the time source specified by timeSource, given the current connections.

If an error occurs, the value in outLatency is unreliable.

Note

This function will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No errors.
Other errors.	Unable to get the latency.

GetSystemTimeSource()

status_t BMediaRoster::GetSystemTimeSource(media_node *clonedTimeSource)

This function returns, in clonedTimeSource, a reference to a clone of the system time source. The system time source is the fallback time source used when no other source is available; its time is derived from the system_time() real-time clock. As such, it’s quite accurate, but has no relevant relationship to the timing of the hardware devices being used for media input and output. Thus it’s not a good choice for a master clock—but it’s there if nothing else is available.

By default, new nodes are slaved to the system time source.

Return Code	Description
`B_OK`	No error cloning the node.
`B_NAME_NOT_FOUND`	The time source couldn’t be cloned.

GetTimeSource(), MakeTimeSourceFor()

status_t BMediaRoster::GetTimeSource(media_node *outNode)

BTimeSource *BMediaRoster::MakeTimeSourceFor(media_node &node)

GetTimeSource() returns, in outNode, the preferred master clock to which other nodes can be slaved. By slaving all nodes to a single master clock, good synchronization can be ensured.

Typically, the preferred master clock will be the same node as the default audio output (assuming that the audio output node is also a BTimeSource, which should be the case). The sound circuitry’s DAC is then used as a timing reference. Although this may be less accurate than the system clock (as defined by the global system_time() function), glitch-free audio performance is best ensured by using the audio output to synchronize media operations.

By default, nodes are slaved to the system time source (see GetSystemTimeSource() above). Usually you’ll want to use this function to obtain a more accurate time source, then slave your nodes to it:

media_node timeSource;
roster->GetTimeSource(&media_node);
roster->SetTimeSourceFor(myNode, timeSource.node);

This will slave the previously-created node myNode to the preferred time source.

MakeTimeSourceFor() returns a BTimeSource object corresponding to the specified node’s time source. This object can then be used to issue BTimeSource calls to determine and adjust timing issues (for instance, to determine the current performance time). When you’re done with the BTimeSource, you should call ReleaseNode() on it.

Return Code	Description
`B_OK`	No error locating the default input node.
`B_NAME_NOT_FOUND`	The default node couldn’t be identified.

InstantiateDormantNode()

status_t BMediaRoster::InstantiateDormantNode(const dormant_node_info &inInfo, media_node *outNode)
status_t BMediaRoster::InstantiateDormantNode(const dormant_node_info &inInfo, media_node *outNode, uint32 flags)

These functions instantiate a node from an add-on, given the information specified in the dormant_node_info structure.

The addon field should be filled out to contain the add-on ID of the add-on from which the node should be instantiated, and the flavor_id should be the flavor ID number the node should be instantiated to process. Typically you’ll use a function such as GetDormantNodes() to find a dormant_node_info structure that describes a suitable node.

When you’re done using the node, and have stopped and disconnected it, you should always call ReleaseNode() to let the Media Server know you’re finished with it. This lets the Media Server track whether or not the node’s add-on can be unloaded, based on the number of applications still using it.

The difference between these two functions is that the second form lets you specify flags controlling how the node is instantiated. The B_FLAVOR_IS_GLOBAL flag instantiates the node in the Media Add-on Server’s memory space, while the B_FLAVOR_IS_LOCAL flag instantiates the node in your application’s memory. Using B_FLAVOR_IS_LOCAL protects other applications—not to mention the Media Server—from being derailed if the node crashes. Whenever possible, you should instantiate nodes locally. You should only use B_FLAVOR_IS_GLOBAL if you need the node to stay around after your application exits.

Return Code	Description
`B_OK`	No error instantiating the node.
`B_NAME_NOT_FOUND`	The requested node couldn’t be instantiated.

MediaFlags()

static ssize_t BMediaRoster::MediaFlags(media_flags flag, void *buffer, size_t bufferSize)

Asks the Media Server about its support for specific features and capabilities.

The specified buffer will be filled with the data indicating the value of the specified flag. If the buffer is too small (as indicated by bufferSize), only the first bufferSize bytes of the result data will be stored in the buffer, but no error will occur.

Constant	Description
`B_MEDIA_FLAGS_VERSION`	Returns the Media Kit version as an int32 value.

If the result is negative, an error occurred, or the Media Server isn’t running.

NodeIDFor()

media_node_id BMediaRoster::NodeIDFor(port_id sourceOrDestinationPort)

Given a source or destination port, this function returns the corresponding node’s ID number.

PrerollNode()

status_t BMediaRoster::PrerollNode(const media_node &node)

Calling PrerollNode() sends a preroll message to the specified node; the node’s Preroll() hook function will be called. When that hook returns, PrerollNode() will also return. A node that’s been prerolled should respond very quickly to a StartNode() call, because the time-consuming setup operations should have been done already by the Preroll() hook.

While it’s not mandatory for an application to call PrerollNode() before calling StartNode(), it’s recommended, because doing so may improve real-time performance once the node is started.

Note

This function will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error sending the set mode request.
`B_NAME_NOT_FOUND`	The requested node couldn’t be cloned.

RegisterNode(), UnregisterNode()

status_t BMediaRoster::RegisterNode(BMediaNode *node)

status_t BMediaRoster::UnregisterNode(BMediaNode *node)

RegisterNode() registers an object of a class derived from BMediaNode with the media roster and assigns it a node_id. This function should be called once a BMediaNode-derived object is fully-constructed and before any attempt is made to connect the node to some other participant in the Media Server.

RegisterNode() is called automatically for nodes instantiated from add-ons, but your application will have to call it for any nodes it creates itself.

If you create your own subclass of BMediaNode, its constructor can call RegisterNode() itself just before returning (it must be the last thing the constructor does).

UnregisterNode() unregisters a node from the Media Server. It’s called automatically by the BMediaNode destructor, but it might be convenient to call it sometime before you delete your node instance, depending on your implementation and circumstances.

These functions are generally only used if you’re creating your own node class.

Return Code	Description
`B_OK`	No error sending the seek request.
`B_BAD_VALUE`	Invalid `BMediaNode` specified.

ReleaseNode()

status_t BMediaRoster::ReleaseNode(const media_node &node)

Releases the specified node, which has previously been obtained by using the InstantiateDormantNode(), GetNodeFor(), or default node functions (such as GetVideoOutput() or GetAudioMixer()).

Return Code	Description
`B_OK`	No error releasing the node.
BMessageerrors.	The node couldn’t be released.

RollNode()

status_t BMediaRoster::RollNode(const media_node &node, bigtime_t startPerformanceTime, bigtime_t stopPerformanceTime, bigtime_t atMediaTime = -B_INFINITE_TIMEOUT)

Atomically queues a start and stop for the given node. The node will start playing at the performance time indicated by startPerformanceTime, and will stop playing at the performance time indicated by stopPerformanceTime.

If the atMediaTime argument is given, a seek to that media time is also queued.

This function is especially useful for the offline rendering case (the B_OFFLINE run mode). It lets you render a certain time range without accidentally going too far; if you queue up a start and stop using Start() and Stop(), the node may have already rendered past your desired stop time before your Stop() call occurs. RollNode() avoids that problem.

Return Code	Description
`B_OK`	No error.
`B_MEDIA_BAD_NODE`	The node isn’t valid.

Roster(), CurrentRoster()

static BMediaRoster *BMediaRoster::Roster(status_t *outError = NULL)

static BMediaRoster *BMediaRoster::CurrentRoster()

Roster() returns a pointer to the default BMediaRoster instance, or creates the BMediaRoster instance if it doesn’t exist yet, then returns a pointer to it. If you don’t want to create the roster if it doesn’t already exist, use the CurrentRoster() function (it returns NULL if there’s no roster).

Since CurrentRoster() doesn’t create a media roster, you obviously must use Roster() at least once in your application to create one.

These static member functions should be called by explicit scope, and never by dereference; this is how you get the BMediaRoster through which all other media roster functions are called. For example:

BMediaRoster* r = BMediaRoster::Roster();
status_t err = r->GetFreeOutputsFor(some_node, some_array, 3, &n);

On return, outError is set to B_OK if the default BMediaRoster was successfully returned, or a negative error code if something went wrong (for example, if the Media Server isn’t running). If outError is NULL, no error code is returned.

In any case, Roster() returns NULL if an error occurs.

SeekNode()

status_t BMediaRoster::SeekNode(const media_node &node, bigtime_t newMediaTime, bigtime_t atPerformanceTime = 0)

Sends the specified node a request that it change its playing location to the media time newMediaTime once the performance time atPerformanceTime is reached.

If the node isn’t running, the seek request is processed immediately, and the atPerformanceTime argument is ignored.

The error returned by this function only indicates whether or not the request was sent successfully; the node may later run into problems trying to perform the seek operation.

Note

If the node is a time source, and you want to operate on the time source aspect of the node (to seek all slaved nodes), you should call SeekTimeSource() instead.

Return Code	Description
`B_OK`	No error sending the seek request.
Other errors	Are node specific

SeekTimeSource()

status_t BMediaRoster::SeekTimeSource(const media_node &timeSource, bigtime_t newPerformanceTime, bigtime_t atRealTime)

Sends the specified timeSource a request that it change the performance time it outputs to its slaved nodes to the time newPerformanceTime once the performance time atRealTime is reached.

If the timeSource isn’t running, the seek request is processed immediately, and the atRealTime argument is ignored.

The error returned by this function only indicates whether or not the request was sent successfully; the node may later run into problems trying to perform the seek operation.

Return Code	Description
`B_OK`	No error sending the seek request.
Other errors	Are node specific

SetAudioInput(), SetVideoInput()

status_t BMediaRoster::SetAudioInput(const media_node &defaultNode)
status_t BMediaRoster::SetAudioInput(const dormant_node_info &defaultNodeInfo)

status_t BMediaRoster::SetVideoInput(const media_node &defaultNode)
status_t BMediaRoster::SetVideoInput(const dormant_node_info &defaultNodeInfo)

These functions set the preferred nodes for audio and video input. If the specified node isn’t capable of being the system default, an error will be returned (for example, nodes defined by an application can’t be the system default—only nodes defined by Media Kit add-ons can be system defaults).

Note

In general, you shouldn’t call these functions unless you’re writing software that reimplements the functionality of the BeOS Audio or Video preference panels.

Return Code	Description
`B_OK`	No error setting the default input node.
`B_NAME_NOT_FOUND`	The default node couldn’t be changed.

SetAudioOutput(), SetVideoOutput()

status_t BMediaRoster::SetAudioOutput(const media_node &defaultNode)
status_t BMediaRoster::SetAudioOutput(const dormant_node_info &defaultNodeInfo)
status_t BMediaRoster::SetAudioOutput(const media_input &inputToOutput)

status_t BMediaRoster::SetVideoOutput(const media_node &defaultNode)
status_t BMediaRoster::SetVideoOutput(const dormant_node_info &defaultNodeInfo)

These functions set the preferred nodes for audio and video output. If the specified node isn’t capable of being the system default, an error will be returned (for example, nodes defined by an application can’t be the system default—only nodes defined by Media Kit add-ons can be system defaults).

Note

In general, you shouldn’t call these functions unless you’re writing software that reimplements the functionality of the BeOS Audio or Video preference panels.

Return Code	Description
`B_OK`	No error setting the default output node.
`B_NAME_NOT_FOUND`	The default node couldn’t be changed.

SetProducerRate()

status_t BMediaRoster::SetProducerRate(const media_node &node, int32 numerator, int32 demominator)

This function is called to tell the producer to resample the data rate by the specified factor. Specifying a value of 1 (ie, numerator/denominator = 1) indicates that the data should be output at the same playback rate that it comes into the node at. The format of the data should be unchanged.

Note

Nodes are not required to support this mechanism for controlling their data rate, so this call may have no effect.

Return Code	Description
`B_OK`	No error.
Other errors.	Returned by `BBufferProducer::SetPlayRate()`.

SetProducerRunModeDelay()

status_t BMediaRoster::SetProducerRunModeDelay(const media_node &node, bigtime_t delay, BMediaNode::run_mode mode = B_RECORDING)

Sets the run mode for the given producer node to mode. Also sets the specified delay to be added to each buffer sent by the producer node. This function should only be called for B_RECORDING mode; it’s provided to compensate when you connect a node that’s in recording mode to a node that isn’t.

Return Code	Description
`B_OK`	No error.
`B_MEDIA_BAD_NODE`	The node is invalid.
Port errors.	An error occurred communicating with the Media Server.

SetRefFor(), GetRefFor()

status_t BMediaRoster::SetRefFor(const media_node &fileInterface, entry_ref &file, bool createAndTruncate, bigtime_t *outDuration)

status_t BMediaRoster::GetRefFor(const media_node &fileInterface, entry_ref *outFile, BMimeType *outMimeType = NULL)

SetRefFor() tells the BFileInterface fileInterface to work on the file whose entry_ref is specified by file. If createAndTruncate is true, any previous file with that reference is deleted and the file will be prepared for new output. If createAndTruncate is false, outDuration will, on return, contain the duration of the performance data found in the file.

GetRefFor() fills out the specified entry_ref, outFile, to reference the file with which the specified fileInterface node is working. If outMimeType isn’t NULL, it’ll contain a BMimeType object describing the file’s type, unless an error occurs.

Note

These functions will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error.
`B_MEDIA_BAD_NODE`	The specified node doesn’t exist, or isn’t a file interface.

SetRunModeNode()

status_t BMediaRoster::SetRunModeNode(const media_node &node, bigtime_t delay, BMediaNode::run_mode newMode)

Sends the specified node a request that it change its policy for handling situations where it falls behind during real-time processing.

The error returned by this function only indicates whether or not the request was sent successfully.

Return Code	Description
`B_OK`	No error sending the set mode request.
`B_BAD_NODE`	The specified node is invalid.

SetTimeSourceFor()

status_t BMediaRoster::SetTimeSourceFor(media_node_id node, media_node_id timeSource)

Tells the specified node to slave its timing to timeSource. Once this is done, the node will receive its notion of the passage of time from timeSource. As such, it will pause whenever timeSource is stopped, and so forth.

Note

By default, nodes are slaved to the system time source, so you only need to call this function if you need to slave a node to a different time source.

The node will take whatever precautions are necessary to remain faithful to the notion of time presented by timeSource without causing glitches in the presentation of its media. For example, if a sound card node has a DAC that drifts from timeSource, it might try to fix the problem by varying the sampling rate slightly, or by dropping or doubling buffers occasionally. This is why you should usually use the preferred time source—rather than the system time source—as your master time source. The preferred time source will usually be derived directly from the DAC being used to produce the media output.

Return Code	Description
`B_OK`	No error.
BMessageerrors.	Unable to set the time source.

SniffRef(), SniffRefFor()

status_t BMediaRoster::SniffRef(const entry_ref &node, uint64 requireNodeKinds, dormant_node_info *outNode, BMimeType *outMimeType = NULL)

status_t BMediaRoster::SniffRefFor(const media_node &fileInterface, const entry_ref &node, uint64 requireNodeKinds, dormant_node_info *outNode, BMimeType *outMimeType = NULL)

SniffRef() asks all BMediaAddOn instances that satisfy the requireNodeKinds restraint to identify the file. The requireNodeKinds argument should contain flags composited from the node_kind constants.

The node that returns the greatest outCapability value will be chosen, and a reference to it put in outNode. The MIME type of the file will be put into outMimeType.

In simpler terms: SniffRef() returns the node that can best handle the media data in the specified file.

SniffRefFor(), on the other hand, asks the specified fileInterface node to examine the file. If the node recognizes the file, the MIME type of the file is stored in the buffer outMimeType, and the node’s capability to handle the file is returned in outCapability.

If the node doesn’t recognize the file, an error is returned. If the node recognizes the file format but finds no recognizable data within the file, outCapability is set to 0.0 and no error is returned.

In either case, the higher the outCapability value returned, the more appropriate the node is for handling the media data in the file.

Note

These functions will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No errors.
`B_MEDIA_BAD_NODE`	The specified node is invalid, or isn’t a file interface.

StartControlPanel()

status_t BMediaRoster::StartControlPanel(const media_node node, Messenger *outMessenger = NULL)

Tells the specified node to start its custom control panel, which is started outside your application. There’s no way to tell when the user has closed the control panel, other than by indirectly detecting possible changes to the node, such as a renegotiation of the format of data being output by the node.

If a BMessenger is provided as input to StartControlPanel(), the function returns in outMessenger a Messenger that can be used to communicate with the control panel.

Note

These functions will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error starting the control panel.
`B_MEDIA_BAD_NODE`	The specified node is invalid.

StartNode()

status_t BMediaRoster::StartNode(const media_node node, bigtime_t atPerformanceTime)
status_t BMediaRoster::StartNode(const media_node node, bigtime_t atPerformanceTime, bool immediate = false)

StartNode() sends the specified node a request to start streaming data at the performance time specified by the atPerformanceTime argument, according to that node’s time source.

By default, nodes are in a stopped state upon creation, so you have to call StartNode() once you have a reference to it before anything will happen. Starting a node that’s already running has no effect.

StopNode() sends node a request to stop streaming data once the specified performance time atPerformanceTime is reached, according to that node’s time source. Stopping a node that’s already stopped has no effect. If immediate is true, the node is instructed to stop immediately and the atPerformanceTime argument is ignored; if immediate is false, the node is stopped at the specified performance time.

In either case, the requested change will occur at the time specified by atPerformanceTime.

Note

If the node is a time source, and you want to operate on the time source aspect of the node (to start or stop all slaved nodes), you should call SeekTimeSource() instead.

The error returned by these functions only indicates whether or not the request was sent successfully; the node may later run into problems trying to start or stop its media and you won’t know it based on the result of these functions.

Note

StopNode() will deadlock if called from a node’s control thread or while the control thread is blocked.

Return Code	Description
`B_OK`	No error sending the start or stop request.
Other errors.	Are node specific.

StartTimeSource(), StopTimeSource()

status_t BMediaRoster::StartTimeSource(const media_node timeSource, bigtime_t atRealTime)

status_t BMediaRoster::StopTimeSource(const media_node timeSource, bigtime_t atRealTime, bool immediate = false)

StartTimeSource() sends the specified timeSource a request to start running at the real time specified by the atRealTime argument.

StopTimeSource() sends node a request to stop the specified timeSource once the specified real time atRealTime is reached. Stopping a time source that’s already stopped has no effect. If immediate is true, the time source is instructed to stop immediately and the atRealTime argument is ignored; if immediate is false, the time source is stopped at the specified real time.

In either case, the requested change will occur at the time specified by atRealTime.

The error returned by these functions only indicates whether or not the request was sent successfully; the node may later run into problems trying to start or stop and you won’t know it based on the result of these functions.

Return Code	Description
`B_OK`	No error sending the start or stop request.
Other errors.	Are node specific.

StartWatching(), StopWatching()

status_t BMediaRoster::StartWatching(const BMessenger &notifyHandler)
status_t BMediaRoster::StartWatching(const BMessenger &notifyHandler, int32 notificationType)
status_t BMediaRoster::StartWatching(const BMessenger &notifyHandler, const media_node &node, int32 notificationType)

status_t BMediaRoster::StopWatching(const BMessenger &notifyHandler)
status_t BMediaRoster::StopWatching(const BMessenger &notifyHandler, int32 notificationType)
status_t BMediaRoster::StopWatching(const BMessenger &notifyHandler, const media_node &node, int32 notificationType)

StartWatching() registers the specified BHandler or BLooper as a recipient of notification messages from the Media Server. StopWatching() cancels this registration so that no further notifications will be sent.

If you’re only interested in a particular notification type, you can specify that code in the notificationType argument. If you don’t specify a notification type, B_MEDIA_WILDCARD is assumed; this matches all notification types. You can also specify that you want to watch a specific node; if you don’t specify a node, you’ll receive notifications for all nodes.

Events are sent to registered BHandlers and BLoopers when certain events happen, such as nodes being created or deleted, or connections being made or broken.

See “Notification Messages” for a list of the notifications you can receive, and the formats of the corresponding messages.

Although the Media Server will automatically cancel notifications to BHandlers and BLoopers that go away without explicitly calling StopWatching(), this detection is expensive and may briefly interrupt the media system, so you should always call StopWatching() before allowing a BHandler or BLooper to go away.

Return Code	Description
`B_OK`	No error cloning the node.
`B_NAME_NOT_FOUND`	The requested node couldn’t be cloned.

SyncToNode()

status_t BMediaRoster::SyncToNode(const media_node node, bigtime_t atPerformanceTime, bigtime_t timeout = B_INFINITE_TIMEOUT)

If you want to detect the arrival of a specific performance time on a given node, you can do that by calling SyncToNode(). Specify the node you want to monitor in node, and the time you want to be notified of in atPerformanceTime. You can, optionally, specify a timeout; if the sync hasn’t occurred in timeout microseconds, the request will time out.

This function doesn’t return until either the specified performance time arrives, or the sync operation times out.

Return Code	Description
`B_OK`	All’s well.
`B_MEDIA_BAD_NODE`	The specified node is invalid.
`B_TIMED_OUT`	The request timed out.
Port errors.	An error occurred communicating with the Media Server.

Constants¶

connect_flags¶

Declared in: media/MediaRoster.h

Constant	Description
`B_CONNECT_MUTED`	The connection should be muted on creation.