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69 lines
1.7 KiB
Markdown
69 lines
1.7 KiB
Markdown
---
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title: The query function
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...
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# The query function
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Through the query function, your element will receive queries that it
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has to reply to. These are queries like position, duration but also
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about the supported formats and scheduling modes your element supports.
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Queries can travel both upstream and downstream, so you can receive them
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on sink pads as well as source pads.
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Below follows a very simple query function that we install on the source
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pad of our element.
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``` c
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static gboolean gst_my_filter_src_query (GstPad *pad,
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GstObject *parent,
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GstQuery *query);
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[..]
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static void
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gst_my_filter_init (GstMyFilter * filter)
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{
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[..]
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/* configure event function on the pad before adding
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* the pad to the element */
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gst_pad_set_query_function (filter->srcpad,
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gst_my_filter_src_query);
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[..]
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}
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static gboolean
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gst_my_filter_src_query (GstPad *pad,
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GstObject *parent,
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GstQuery *query)
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{
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gboolean ret;
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GstMyFilter *filter = GST_MY_FILTER (parent);
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switch (GST_QUERY_TYPE (query)) {
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case GST_QUERY_POSITION:
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/* we should report the current position */
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[...]
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break;
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case GST_QUERY_DURATION:
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/* we should report the duration here */
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[...]
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break;
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case GST_QUERY_CAPS:
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/* we should report the supported caps here */
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[...]
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break;
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default:
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/* just call the default handler */
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ret = gst_pad_query_default (pad, parent, query);
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break;
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}
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return ret;
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}
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```
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It is a good idea to call the default query handler
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`gst_pad_query_default ()` for unknown queries. Depending on the query
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type, the default handler will forward the query or simply unref it.
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