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149 lines
4.6 KiB
Text
149 lines
4.6 KiB
Text
Messages
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--------
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Messages are refcounted lightweight objects to signal the application
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of pipeline events.
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Messages are implemented as a subclass of GstMiniObject with a generic
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GstStructure as the content. This allows for writing custom messages without
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requiring an API change while allowing a wide range of different types
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of messages.
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Messages are posted by objects in the pipeline and are passed to the
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application using the GstBus (See also part-gstbus.txt and part-gstpipeline.txt).
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Message types
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~~~~~~~~~~~~~
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GST_MESSAGE_EOS:
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Posted by sink elements. This message is posted to the application when
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all the sinks in a pipeline posted an EOS message. When performing a seek,
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the EOS state of the pipeline and sinks is undone.
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GST_MESSAGE_ERROR:
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An element in the pipeline got into an error state. The message carries
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a GError and a debug string describing the error. This usually means that
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part of the pipeline is not streaming anymore.
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GST_MESSAGE_WARNING:
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An element in the pipeline encountered a condition that made it produce a
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warning. This could be a recoverable decoding error or some other non fatal
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event. The pipeline continues streaming after a warning.
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GST_MESSAGE_INFO:
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An element produced an informational message.
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GST_MESSAGE_TAG:
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An element decoded metadata about the stream. The message carries a GstTagList
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with the tag information.
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GST_MESSAGE_BUFFERING:
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An element is buffering data and that could potentially take some time. This
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message is typically emited by elements that perform some sort of network
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buffering. While the pipeline is buffering it should remain in the PAUSED
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state. When the buffering is finished, it can resume PLAYING.
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GST_MESSAGE_STATE_CHANGED:
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An element changed state in the pipeline. The message carries the old, new
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and pending state of the element.
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GST_MESSAGE_STATE_DIRTY:
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An internal message used to instruct a pipeline hierarchy that a state
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recalculation must be performed because of an ASYNC state change completed.
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This message is not used anymore.
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GST_MESSAGE_STEP_DONE:
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An element stepping frames has finished. This is currently not used.
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GST_MESSAGE_CLOCK_PROVIDE:
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An element notifies it capability of providing a clock for the pipeline.
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GST_MESSAGE_CLOCK_LOST:
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The current clock as selected by the pipeline became unusable. The pipeline
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will select a new clock on the next PLAYING state change.
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GST_MESSAGE_NEW_CLOCK:
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A new clock was selected for the pipeline.
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GST_MESSAGE_STRUCTURE_CHANGE:
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The pipeline changed of structure, This means elements were added or removed or
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pads were linked or unlinked. This messages is not yet used.
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GST_MESSAGE_STREAM_STATUS:
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Posted by an element when it start/stop/pauses a streaming task. It
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contains information about the reason why the stream state changed along
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with the thread id. The application can use this information to detect
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failures in streaming threads. It can also be used to adjust streaming
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thread priorities by the application.
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GST_MESSAGE_APPLICATION:
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The application posted a message. This message must be used when the
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application posts a message on the bus.
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GST_MESSAGE_ELEMENT:
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Element-specific message, see the specific element's documentation
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GST_MESSAGE_SEGMENT_START:
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An element started playback of a new segment. This message is not forwarded
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the application but is used internally to schedule SEGMENT_DONE messages.
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GST_MESSAGE_SEGMENT_DONE:
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An element or bin completed playback of a segment. This message is only posted
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on the bus if a SEGMENT seek is performed on a pipeline.
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GST_MESSAGE_DURATION_CHANGED:
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An element posts this message when it has detected or updated the stream duration.
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GST_MESSAGE_ASYNC_START:
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Posted by sinks when they start an asynchronous state change.
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GST_MESSAGE_ASYNC_DONE:
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Posted by sinks when they receive the first data buffer and complete the
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asynchronous state change.
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GST_MESSAGE_LATENCY:
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Posted by elements when the latency in a pipeline changed and a new global
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latency should be calculated by the pipeline or application.
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GST_MESSAGE_REQUEST_STATE:
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Posted by elements when they want to change the state of the pipeline they
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are in. A typical use case would be an audio sink that requests the pipeline
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to pause in order to play a higher priority stream.
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GST_MESSAGE_STEP_START:
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A Stepping operation has started.
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GST_MESSAGE_QOS:
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A buffer was dropped or an element changed its processing strategy for
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Quality of Service reasons.
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GST_MESSAGE_PROGRESS:
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A progress message was posted. Progress messages inform the application about
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the state of asynchronous operations.
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