Call this from your derived node's constructor.

The node is created with a reference count of 1; the count is incremented each time the Acquire() call is issued, and decremented each time Release() is called. When the reference count becomes zero, the node is deleted.

You may never delete a BMediaNode because you don't know for certain when the Media Server is done with it. Instead, the Media Server maintains a reference count for the node, and when it is no longer in use, the node will be deleted automatically.

Acquire() returns a pointer to the node, after incrementing the node's reference count.

Release() releases the node by decrementing its reference count. If the count reaches zero, the node is deleted and NULL is returned; otherwise, a pointer to the node is returned.

Note

Although you usually can't call node member functions directly from within an application, you can call Acquire() and Release() directly if the node is subclassed within the application itself (rather than in an add-on).

Adds a kind to the set of kinds supported by the node. This lets the system know what types of node interfaces are supported by the node's implementation. Possible values include B_BUFFER_PRODUCER (which indicates that the node implements the BBufferProducer protocol) and B_PHYSICAL_INPUT (which indicates that the node implements a physical input, such as a sound digitizing input device). For a complete list of kind values, see node_kind.

Note

In general, you don't need to call this function. The base system classes call AddNodeKind() automatically to set up the node type flags; for example, a BBufferProducer automatically calls AddNodeKind(B_BUFFER_PRODUCER). The only time it's necessary go call AddNodeKind() is if the node you're implementing is a physical device or a mixer, in which case you need to add the B_PHYSICAL_INPUT, B_PHYSICAL_OUTPUT, or B_SYSTEM_MIXER flag.

Implement this function to return a pointer to the BMediaAddOn that instantiated the node. If the node lives in an application (rather than in an add-on), return NULL. If the node is in an add-on, outInternalID should be changed to contain the internal ID number of the node within the add-on.

Your node should implement the AddTimer() function to remember the cookie and time given. When the time toPerformanceTime is reached, your node should call TimerExpired() with the corresponding cookie value, passing the recorded toPerformanceTime value as the notifyPoint argument. This will, in turn, cause the BMediaRoster::SyncToNode() call that instigated the timer to return to the caller.

Your implementation of AddTimer() should return B_OK if all is well; otherwise it should return an appropriate error code.

Returns the port_id of the port to which the node listens for requests. Your node must implement this to return a valid Kernel Kit port.

The DeleteHook() function is called to delete the BMediaNode object. You may augment this if you need to perform additional work before the node is deleted, but you should always either include the line:

delete this;

or you should call through to the inherited form of the function. Return B_OK if the node was deleted successfully, otherwise return an appropriate error code.

Implement this function to fill the outAttributes array (which has room for inMaxCount attributes) with your node's attributes.

Return B_OK if all is well, or return an appropriate error code.

If your node receives a message that neither the node, nor any interface from which the node is derived, understands the message, pass the message along to this function, which will work magic to deal with the problem one way or another. All arguments received by the HandleMessage() function should be passed directly through to HandleBadMessage().

Given a message received on the control port, this function dispatches the message to the appropriate BMediaNode hook function. If the message doesn't correspond to a hook function, B_ERROR is returned.

When you implement a media node of your own (derived from BBufferConsumer, BBufferProducer, etc), you always need to call through to BMediaNode::HandleMessage() from your node's implementation of HandleMessage(). This is crucial, to be sure that every ancestor of your node gets to look at the message and attempt to process it.

For example, if your node inherits from both BBufferProducer and BBufferConsumer, you should call BBufferProducer::HandleMessage() and BBufferConsumer::HandleMessage(), then BMediaNode::HandleMessage(), like this:

virtual status_t MyBufferProducerConsumer::HandleMessage(int32 message,
         const void* data, size_t size) {
   if (message == SOME_THING_I_DO) {
      DoWhatever();
   }
   else if (BBufferConsumer::HandleMessage(message, data, size) &&
            BBufferProducer::HandleMessage(message, data, size) &&
            BMediaNode::HandleMessage(message, data, size)) {
      BMediaNode::HandleBadMessage(message, data, size);
   }
}

Note that BMediaNode::HandleBadMessage() is called if none of the HandleMessage() implementations accept the message.

Values of message between 0x60000000 and 0x7FFFFFFF are available for use by applications. Values below 0x60000000 are reserved for use by the Media Kit, and typically correspond to specific virtual hook functions within your node. If you can show just cause for needing to know the message value for a particular hook, you can try emailing devsupport@be.com and see if we agree with you, in which case we may share that information.

Don't reverse-engineer the message values; if you really need to know, ask us. Otherwise, we won't know that a particular message code number shouldn't be changed. In general, it's a bad idea to rely on specific values, although there may be cases in which it's necessary.

Returns the media_node_id assigned to the node by the Media Server. The result is 0 if the node hasn't been registered yet, and negative if an error occurred while attempting to register the node.

Returns a bit mask indicating what interfaces the node implements. See node_kind for a list of valid interface kinds.

Returns a human-readable string specifying the node's name. This pointer is only valid until you Release() the node; after that, the pointer may point into empty space.

This function, intended primarily for use by BBufferConsumer nodes, creates and returns a new change tag value.

Returns the media_node structure that will be used by an application when accessing this node via the media roster.

The Media Server calls this hook function after the node has been registered.

When you've finished handling a stop request (buffers will no longer be flowing), call this function. If anyone is listening for stop notifications from you, they'll be notified. The whenPerformanceTime argument should be the performance time of the stop command that was handled.

Anyone listening for node stop messages will be notified; this lets applications running in offline (rendering) mode know when the node has actually completed its work.

If your node is a BBufferProducer, downstream consumers will be notified that your node stopped (automatically, no less) through the BBufferConsumer::ProducerDataStatus(B_PRODUCER_STOPPED) call. This lets offline rendering nodes know when each of their inputs have no more data to send for the current roll.

Note

This is especially important for nodes that can be run in B_OFFLINE mode.

This hook function may be called before your node receives a Start() message if the application using the node calls BMediaRoster::PrerollNode(). This gives the node a chance to prepare the media so that when the media is started, the response is as fast as possible.

Transmits the error code specified by whichError to anyone that's receiving notifications from this node (see BMediaRoster::StartWatching() and BMediaRoster::StopWatching() on ). If info isn't NULL, it's used as a model message for the error notification message.

This function is called whenever a request issued by the node is completed. The info structure describes the results of the request.

The change_tag field in the info structure identifies the request that has been completed; this is the same value passed into the function that initiated the request.

Return B_OK if you're happy, otherwise return an appropriate error code.

RunMode() returns the node's current run_mode setting.

The SetRunMode() hook function is called when someone requests that your node's run mode be changed.

This hook function is called when a node is asked to seek to the specified mediaTime by a call to the BMediaRoster.

The specified performanceTime, the time at which the node should begin the seek operation, may be in the future.

Note

Your node is required to queue at least one each of start, stop, and seek requests, so that applications can establish, for example, both the start and stop time without having to monitor your node's progress. The actual size of these three queues is up to you. When the specified time arrives, the request should be filled.

A mediaTime value of 0 indicates the beginning of the media data.

The SetTimeSource() hook function is called when someone has requested that the node be slaved to a new time source. Augment this function to make whatever adjustments you need to make to operate at the new time scale.

TimeSource() returns a pointer to the BTimeSource to which the node is currently slaved. If no time source has been explicitly requested, the system time source is in use, and that's what gets returned.

Warning

The BTimeSource object returned by TimeSource() is only valid until the next call to HandleMessage() on that object. Therefore, if your node runs more than one thread, you need to serialize calls to TimeSource() (as well as usage of the returned objects) with calls to HandleMessage() This isn't a problem if you follow the recommended policy of running a single thread that monitors the service port with read_port_etc() and calls HandleMessage() only when a message is actually received.

This hook function is called when a node is started by a call to the BMediaRoster.

The specified performanceTime, the time at which the node should start running, may be in the future.

Note

Your node is required to queue at least one each of start, stop, and seek requests, so that applications can establish, for example, both the start and stop time without having to monitor your node's progress. The actual size of these three queues is up to you. When the specified time arrives, the request should be filled.

This hook function is called when a node is stopped by a call to the BMediaRoster.

The specified performanceTime, the time at which the node should stop, may be in the future.

If immediate is true, your node should ignore the performanceTime value and synchronously stop performance. When Stop() returns, you're promising not to write into any BBuffers you may have received from your downstream consumers, and you promise not to send any more buffers until Start() is called again.

Note

Your node is required to queue at least one each of start, stop, and seek requests, so that applications can establish, for example, both the start and stop time without having to monitor your node's progress. The actual size of these three queues is up to you. When the specified time arrives, the request should be filled.

Nodes must recycle all buffers they may be holding onto when they're stopped.

This hook function is called when the time source to which the node is slaved is repositioned (via a seek operation) such that there will be a sudden jump in the performance time progression as seen by the node. The newPerformanceTime argument indicates the new performance time; the change should occur at the real time specified by the atRealTime argument.

The node should respond to this call by preparing for this change, so a serious stutter, failure, or acceleration in performance doesn't occur. Appropriate measures should be taken to minimize the impact on the performance quality; for example, a segment of the sound could be looped or skipped smoothly.

Your implementation of TimeWarp() should call through to BMediaNode::TimeWarp() as well as all other inherited forms of TimeWarp().

This function waits until either real time specified by waitUntil or a message is received on the control port.. The flags are currently unused and should be 0.

When a message is received, the appropriate HandleMessage() calls are made given the class derivation of the node:

• BMediaNode::HandleMessage() is always called first.

• If the node is derived from BBufferProducer, and the message hasn't been handled yet, BBufferProducer::HandleMessage() is called.

• If the node is derived from BBufferConsumer, and the message hasn't been handled yet, BBufferConsumer::HandleMessage() is called.

• If the node is derived from BFileInterface, and the message hasn't been handled yet, BFileInterface::HandleMessage() is called.

• If the node is derived from BControllable, and the message hasn't been handled yet, BControllable::HandleMessage() is called.

• If the node is derived from BTimeSource, and the message hasn't been handled yet, BTimeSource::HandleMessage() is called.

• If the message still hasn't been handled, the most-derived interface's HandleMessage() function is called.

• If the message hasn't been handled, HandleBadMessage() is called.

Once this has been done, WaitForMessage() returns. As you can see, this can be called from your control port to handle much of the work of processing received messages.

Declared in: media/MediaNode.h

The node_error type defines the errors a node can transmit to BMessengers that have registered to watch the node.

Declared in: media/MediaNode.h

The run_mode type indicates how a node should cope if its performance rate deviates from the desired rate.