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109 lines
4.2 KiB
Text
109 lines
4.2 KiB
Text
Stream Status
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-------------
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This document describes the design and use cases for the stream status
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messages.
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STREAM_STATUS messages are posted on the bus when the state of a streaming
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thread changes. The purpose of this message is to allow the application to
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interact with the streaming thread properties, such as the thread priority or
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the threadpool to use.
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We accommodate for the following requirements:
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- Application is informed when a streaming thread is about to be created. It
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should be possible for the application to suggest a custom GstTask.
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- Application is informed when the status of a streaming thread is changed.
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This can be interesting for GUI application that want to visualize the status
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of the streaming threads (playing/paused/stopped)
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- Application is informed when a streaming thread is destroyed.
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We allow for the following scenarios:
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- Elements require a specific (internal) streaming thread to operate or the
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application can create/specify a thread for the element.
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- Elements allow the application to configure a priority on the threads.
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Use cases
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~~~~~~~~~
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* boost the priority of the udp receiver streaming thread
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.--------. .-------. .------. .-------.
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| udpsrc | | depay | | adec | | asink |
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| src->sink src->sink src->sink |
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'--------' '-------' '------' '-------'
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- when going from READY to PAUSED state, udpsrc will require a streaming
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thread for pushing data into the depayloader. It will post a STREAM_STATUS
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message indicating its requirement for a streaming thread.
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- The application will usually react to the STREAM_STATUS messages with a sync
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bus handler.
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- The application can create and configure a custom GstTask to manage the
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streaming thread or it can ignore the message which will make the element
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use its default GstTask.
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- The application can react to the ENTER/LEAVE stream status message to
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configure the thread right before it is started/stopped. This can be used to
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configure the thread priority.
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- Before the GstTask is changed state (start/pause/stop) a STREAM_STATUS
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message is posted that can be used by the application to keep track of
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the running streaming threads.
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Messages
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~~~~~~~~
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The existing STREAM_STATUS message will be further defined and implemented in
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(selected) elements. The following fields will be contained in the message:
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- "type", GST_TYPE_STREAM_STATUS_TYPE
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- a set of types to control the lifecycle of the thread:
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GST_STREAM_STATUS_TYPE_CREATE: a new streaming thread is going to be
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created. The application has the chance to configure a custom thread.
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GST_STREAM_STATUS_TYPE_ENTER: the streaming thread is about to enter its
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loop function for the first time.
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GST_STREAM_STATUS_TYPE_LEAVE: the streaming thread is about to leave its
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loop.
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GST_STREAM_STATUS_TYPE_DESTROY: a streaming thread is destroyed
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- A set of types to control the state of the threads:
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GST_STREAM_STATUS_TYPE_START: a streaming thread is started
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GST_STREAM_STATUS_TYPE_PAUSE: a streaming thread is paused
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GST_STREAM_STATUS_TYPE_STOP: a streaming thread is stopped
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- "owner", GST_TYPE_ELEMENT
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The owner element of the thread. The message source will contain the pad
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(or one of the pads) that will produce data by this thread. If this thread
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does not produce data on a pad, the message source will contain the owner
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as well. The idea is that the application should be able to see from the
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element/pad what function this thread has in the context of the
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application and configure the thread appropriatly.
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- "object", G_TYPE, GstTask/GThread
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A GstTask/GThread controlling this streaming thread. This can be NULL when
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the object controlling the streaming thread is not yet created.
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- "flow-return", GstFlowReturn
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A status code for why the thread state changed. when threads are created
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and started, this is usually GST_FLOW_OK but when they are stopping it
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contains the reason code why it stopped.
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- "reason", G_TYPE_STRING
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A string describing the reason why the thread started/stopped/paused.
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Can be NULL if no reason is given.
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Events
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~~~~~~
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