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Original commit message from CVS: 2005-05-06 Andy Wingo <wingo@pobox.com> * gst/gstquery.h * gst/gstquery.c (_gst_query_initialize): Extend GstQuery from GstData, init a memchunk. (standard_definitions): Add a few query types, deprecate a few. (gst_query_get_type): New proc. (_gst_query_copy, _gst_query_free, gst_query_new): GstData implementation. (gst_query_new_application, gst_query_get_structure): New public procs. * docs/design/draft-query.txt: Removed LINKS from the query types, because all the rest can be dispatched to other pads -- seemed ugly to have a query that couldn't be dispatched. internal_links is fine as a pad method. * gst/gstpad.h: Add query2 as a pad method, add the new functions in gstpad.c, but maintain binary compatibility for the moment. Will fix before 0.9 is out. * gst/gstqueryutils.c: * gst/gstqueryutils.h: New files, implement 3 methods for each query type: parse_query, parse_response, and set. Probably need an allocator as well. * gst/gst.h: Add gstquery.h and gstqueryutils.h to the list. * gst/elements/gstfilesink.c (gst_filesink_query2): * gst/base/gstbasesrc.c (gst_basesrc_query2): Replace old query, query_types, and formats methods. * gst/gstpad.c (gst_pad_query2, gst_pad_query2_default) (gst_pad_set_query2_function): New functions. (gst_real_pad_init): Set query2_default as the default query2 function. Basically just dispatches to internally linked pads. Needs review! * gst/gstdata_private.h (_GST_DATA_INIT): Set data->refcount to 1 without using the atomic operations. Only one thread can possibly be accessing the data at this point. Changed so as to avoid gst_atomic operations.
90 lines
2.6 KiB
Plaintext
90 lines
2.6 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 GstData 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
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- start position
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- current position
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- end position
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- length
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- GST_QUERY_LATENCY:
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- get amount of buffering
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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.
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Also????
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- GST_QUERY_CAPS:
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