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Original commit message from CVS: * docs/design/draft-latency.txt: * docs/design/draft-push-pull.txt: * docs/design/draft-tagreading.txt: * docs/design/part-MT-refcounting.txt: * docs/design/part-activation.txt: * docs/design/part-block.txt: * docs/design/part-element-source.txt: * docs/design/part-events.txt: * docs/design/part-gstbin.txt: * docs/design/part-gstelement.txt: * docs/design/part-gstobject.txt: * docs/design/part-gstpipeline.txt: * docs/design/part-messages.txt: * docs/design/part-preroll.txt: * docs/design/part-push-pull.txt: * docs/design/part-qos.txt: * docs/design/part-query.txt: * docs/design/part-scheduling.txt: * docs/design/part-seeking.txt: * docs/design/part-segments.txt: * docs/design/part-states.txt: Documentation updates and typo fixes.
90 lines
2.7 KiB
Plaintext
90 lines
2.7 KiB
Plaintext
DRAFT Query
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-----------
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Purpose
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Queries are used to get information about the stream.
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A query is started on a specific pad and travels up or downstream.
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Types of queries
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- get length of stream
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- get position in stream
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- get seeking capabilities
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- get latency
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- convert one value to another
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- query supported formats
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- query internal links.
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Current implementation
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The current implementation of query requires pads to implement the
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following functions:
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gboolean (*GstPadConvertFunction) (GstPad *pad,
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GstFormat src_format, gint64 src_value,
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GstFormat *dest_format, gint64 *dest_value);
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gboolean (*GstPadQueryFunction) (GstPad *pad, GstQueryType type,
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GstFormat *format, gint64 *value);
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GList* (*GstPadIntLinkFunction) (GstPad *pad);
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const GstFormat* (*GstPadFormatsFunction) (GstPad *pad);
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const GstEventMask* (*GstPadEventMaskFunction) (GstPad *pad);
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const GstQueryType* (*GstPadQueryTypeFunction) (GstPad *pad);
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Most of these functions are not very extensible in particular,
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the queryfunction can only return one value.
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Requirements
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- multiple return values, grouped together when they make sense.
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- one pad function to perform the query
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- extensible queries.
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Proposition
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- define GstQuery extending GstMiniObject and containing a GstStructure (see GstMessage)
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- define standard query types (see proposed types)
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- define methods to create a parse the results in the GstQuery.
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- define pad method:
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gboolean (*GstPadQueryFunction) (GstPad *pad, GstQuery *query);
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pad returns result in query structure and TRUE as result or FALSE when
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query is not supported.
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Proposed types
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- GST_QUERY_SEEKING:
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get info on how seeking can be done
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- getrange, with/without offset/size
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- ranges where seeking is efficient (for caching network sources)
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- flags describing seeking behaviour (forward, backward, segments,
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play backwards, ...)
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- GST_QUERY_POSITION:
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get info on current position of the stream in stream_time.
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- GST_QUERY_DURATION:
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get info on the total duration of the stream.
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- GST_QUERY_LATENCY:
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get amount of latency introduced in the pipeline.
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- GST_QUERY_SEGMENT:
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get info about the currently configured playback segment.
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- GST_QUERY_CONVERT:
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convert format/value to another format/value pair.
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- GST_QUERY_FORMATS:
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return list of supported formats that can be used for GST_QUERY_CONVERT.
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