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108 lines
4.2 KiB
Markdown
108 lines
4.2 KiB
Markdown
# 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 messages 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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## Requirements and scenarios
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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 appropriately.
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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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