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Original commit message from CVS: * docs/design/draft-push-pull.txt: * docs/design/part-MT-refcounting.txt: * docs/design/part-TODO.txt: * docs/design/part-caps.txt: * docs/design/part-events.txt: * docs/design/part-gstbus.txt: * docs/design/part-gstpipeline.txt: * docs/design/part-messages.txt: * docs/design/part-push-pull.txt: * docs/design/part-query.txt: Some more docs.
70 lines
2 KiB
Plaintext
70 lines
2 KiB
Plaintext
Query
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-----
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Queries are used to get information about the state of the stream.
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Various queries exist such as get the total length and the position
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A query can be performed on a pad or on an element. Both the element
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and the pad query have default behaviour unless a custom query handler
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is installed.
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The default pad query handler will forward the query to an internally
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linked pad. This internally linked pad is either obtained by calling
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the internal_links function of the pad or by using the default
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function (which selects the pads with oposite directions from the parent
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element).
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The default element query function will select a random source pad to
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send the event to.
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The pad query function has the following prototype:
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gboolean (*GstPadQueryFunction) (GstPad *pad, GstQueryType type,
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GstFormat *format, gint64 *value);
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The query function can return a single value in one of the defined
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formats.
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The function returns TRUE if the query could be performed. The returned
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values are undefined when this function returns FALSE.
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Query types
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-----------
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GST_QUERY_TOTAL:
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get the total length of the stream in the given format.
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GST_QUERY_POSITION:
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get the current position in the stream in the given format.
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GST_QUERY_LATENCY:
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get the latency introduced in the stream in the given format.
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This query can be used to retrieve how much data is queued in a
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queue or in a hardware device such as an audio sink.
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GST_QUERY_JITTER:
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Get the jitter, this is the difference between the expected and real
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time a buffer is captured or played.
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GST_QUERY_START:
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Query the position in the stream where the last start position was
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configured. When a seek was performed to play a stream from A to B,
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this query will return A.
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GST_QUERY_SEGMENT_END:
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Query the position in the stream where the last end position was
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configured. When a seek was performed to play a stream from A to B,
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this query will return B.
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GST_QUERY_RATE:
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Query the current playback rate of the stream.
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