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107 lines
4.1 KiB
Markdown
107 lines
4.1 KiB
Markdown
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# Stream Status
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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
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streaming thread changes. The purpose of this message is to allow the
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application to interact with the streaming thread properties, such as
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the thread priority or 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
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created. It should be possible for the application to suggest a
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custom GstTaskPool.
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- Application is informed when the status of a streaming thread is
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changed. This can be interesting for GUI application that want to
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visualize the status of the streaming threads
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(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
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or the application can create/specify a thread for the element.
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- Elements allow the application to configure a priority on the
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threads.
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## Use cases
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- boost the priority of the udp receiver streaming thread
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```
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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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```
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- when going from READY to PAUSED state, udpsrc will require a
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streaming thread for pushing data into the depayloader. It will
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post a STREAM_STATUS message indicating its requirement for a
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streaming thread.
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- The application will usually react to the STREAM_STATUS
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messages with a sync bus handler.
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- The application can configure the GstTask with a custom
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GstTaskPool to manage the streaming thread or it can ignore the
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message which will make the element use its default GstTaskPool.
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- The application can react to the ENTER/LEAVE stream status
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message to configure the thread right before it is
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started/stopped. This can be used to configure the thread
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priority.
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- Before the GstTask is changed state (start/pause/stop) a
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STREAM_STATUS message is posted that can be used by the
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application to keep track of the running streaming threads.
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## Messages
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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
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to be created. The application has the chance to configure a custom
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thread. GST_STREAM_STATUS_TYPE_ENTER: the streaming thread is
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about to enter its loop function for the first time.
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GST_STREAM_STATUS_TYPE_LEAVE: the streaming thread is about to
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leave its loop. GST_STREAM_STATUS_TYPE_DESTROY: a streaming
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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: The owner element of the thread. The
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message source will contain the pad (or one of the pads) that will
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produce data by this thread. If this thread does not produce data on
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a pad, the message source will contain the owner as well. The idea
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is that the application should be able to see from the element/pad
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what function this thread has in the context of the application and
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configure the thread appropriatly.
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- **`object`**: G_TYPE, GstTask/GThread: A GstTask/GThread controlling
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this streaming thread.
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- **`flow-return`**: GstFlowReturn: A status code for why the thread state
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changed. when threads are created and started, this is usually
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GST_FLOW_OK but when they are stopping it contains the reason code
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why it stopped.
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- **`reason`**: G_TYPE_STRING: A string describing the reason why the
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thread started/stopped/paused. Can be NULL if no reason is given.
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## Events
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FIXME
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