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