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design: gstbin: add missing markup
Also fix some minor grammar issues.
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1 changed files with 16 additions and 16 deletions
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# GstBin
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GstBin is a container element for other GstElements. This makes it
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`GstBin` is a container element for other `GstElements`. This makes it
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possible to group elements together so that they can be treated as one
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single GstElement. A GstBin provides a GstBus for the children and
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single `GstElement`. A `GstBin` provides a `GstBus` for the children and
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collates messages from them.
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## Add/removing elements
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## Retrieving elements
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GstBin provides a number of functions to retrieve one or more children
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`GstBin` provides a number of functions to retrieve one or more children
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from itself. A few examples of the provided functions:
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* `gst_bin_get_by_name()` retrieves an element by name.
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## element management
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The most important function of the GstBin is to distribute all
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GstElement operations on itself to all of its children. This includes:
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The most important function of the `GstBin` is to distribute all
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`GstElement` operations on itself to all of its children. This includes:
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- state changes
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## GstBus
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The GstBin creates a GstBus for its children and distributes it when
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The `GstBin` creates a `GstBus` for its children and distributes it when
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child elements are added to the bin. The bin attaches a sync handler to
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receive messages from children. The bus for receiving messages from
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children is distinct from the bin’s own externally-visible GstBus.
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children is distinct from the bin’s own externally-visible `GstBus`.
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Messages received from children are forwarded intact onto the bin’s
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external message bus, except for EOS and SEGMENT_START/DONE which are
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external message bus, except for EOS and `SEGMENT_START`/`DONE` which are
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handled specially.
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ASYNC_START/ASYNC_STOP messages received from the children are used to
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`ASYNC_START`/`ASYNC_STOP` messages received from the children are used to
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trigger a recalculation of the current state of the bin, as described in
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[states](design/states.md).
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The application can retrieve the external GstBus and integrate it in the
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The application can retrieve the external `GstBus` and integrate it in the
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mainloop or it can just `pop()` messages off in its own thread.
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When a bin goes to READY it will clear all cached messages.
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A bin collects `SEGMENT_START` messages but does not post them to the
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application. It counts the number of `SEGMENT_START` messages and posts a
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`SEGMENT_STOP` message to the application when an equal number of
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`SEGMENT_STOP` messages where received.
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`SEGMENT_STOP` messages were received.
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The cached SEGMENT_START/STOP messages are cleared when going to READY.
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The cached `SEGMENT_START`/`STOP` messages are cleared when going to READY.
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## DURATION
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When a DURATION query is performed on a bin, it will forward the query
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to all its sink elements. The bin will calculate the total duration as
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the MAX of all returned durations and will then cache the result so that
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any further query can use the cached version. The reason for caching the
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any further queries can use the cached version. The reason for caching the
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result is because the duration of a stream typically does not change
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that often.
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## Subclassing
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Subclasses of GstBin are free to implement their own add/remove
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implementations. It is a good idea to update the GList of children so
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Subclasses of `GstBin` are free to implement their own add/remove
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functions. It is a good idea to update the `GList` of children so
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that the `_iterate()` functions can still be used if the custom bin
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allows access to its children.
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Any bin subclass can also implement a custom message handler by
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overriding the default message handler.
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overriding the default one.
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