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41 lines
1.9 KiB
Text
41 lines
1.9 KiB
Text
GstBus
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------
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The GstBus is an object responsible for delivering GstMessages in
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a first-in first-out way from the streaming threads to the application.
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Since the application typically only wants to deal with delivery of these
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messages from one thread, the GstBus will marshall the messages between
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different threads. This is important since the actual streaming of media
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is done in another threads (streaming threads) than the application. It is
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also important to not block the streaming threads while the application deals
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with the message.
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The GstBus provides support for GSource based notifications. This makes it
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possible to handle the delivery in the glib mainloop. Different GSources
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can be added to the same bin provided they listen to different message types.
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A message is posted on the bus with the gst_bus_post() method. With the
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gst_bus_peek() and _pop() methods one can look at or retrieve a previously
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posted message.
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The bus can be polled with the gst_bus_poll() method. This methods blocks
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up to the specified timeout value until one of the specified messages types
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is posted on the bus. The application can then _pop() the messages from the
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bus to handle them.
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It is also possible to get messages from the bus without any thread
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marshalling with the gst_bus_set_sync_handler() method. This makes it
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possible to react to a message in the same thread that posted the
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message on the bus. This should only be used if the application is able
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to deal with messages from different threads.
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If no messages are popped from the bus with either a GSource or gst_bus_pop(),
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they remain on the bus.
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When a pipeline or bin goes from READY into NULL state, it will set its bus
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to flushing, ie. the bus will drop all existing and new messages on the bus,
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This is necessary because bus messages hold references to the bin/pipeline
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or its elements, so there are circular references that need to be broken if
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one ever wants to be able to destroy a bin or pipeline properly.
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