|  |  |  | GStreamer 0.10 Core Reference Manual |  | 
|---|---|---|---|---|
| GstQueryGstQuery — Dynamically register new query types. Provide functions to create queries, and to set and parse values in them. | 
#include <gst/gst.h>
                    GstQuery;
enum                GstQueryType;
#define             GST_QUERY_TYPE                      (query)
#define             GST_QUERY_TYPE_NAME                 (query)
                    GstQueryTypeDefinition;
const gchar*        gst_query_type_get_name             (GstQueryType query);
GQuark              gst_query_type_to_quark             (GstQueryType query);
GstQueryType        gst_query_type_register             (const gchar *nick,
                                                         const gchar *description);
GstQueryType        gst_query_type_get_by_nick          (const gchar *nick);
gboolean            gst_query_types_contains            (const GstQueryType *types,
                                                         GstQueryType type);
const GstQueryTypeDefinition* gst_query_type_get_details
                                                        (GstQueryType type);
GstIterator*        gst_query_type_iterate_definitions  (void);
#define             gst_query_ref                       (q)
#define             gst_query_unref                     (q)
#define             gst_query_copy                      (q)
#define             gst_query_make_writable             (q)
GstQuery*           gst_query_new_application           (GstQueryType type,
                                                         GstStructure *structure);
GstStructure*       gst_query_get_structure             (GstQuery *query);
GstQuery*           gst_query_new_convert               (GstFormat src_format,
                                                         gint64 value,
                                                         GstFormat dest_format);
void                gst_query_set_convert               (GstQuery *query,
                                                         GstFormat src_format,
                                                         gint64 src_value,
                                                         GstFormat dest_format,
                                                         gint64 dest_value);
void                gst_query_parse_convert             (GstQuery *query,
                                                         GstFormat *src_format,
                                                         gint64 *src_value,
                                                         GstFormat *dest_format,
                                                         gint64 *dest_value);
GstQuery*           gst_query_new_position              (GstFormat format);
void                gst_query_set_position              (GstQuery *query,
                                                         GstFormat format,
                                                         gint64 cur);
void                gst_query_parse_position            (GstQuery *query,
                                                         GstFormat *format,
                                                         gint64 *cur);
GstQuery*           gst_query_new_duration              (GstFormat format);
void                gst_query_set_duration              (GstQuery *query,
                                                         GstFormat format,
                                                         gint64 duration);
void                gst_query_parse_duration            (GstQuery *query,
                                                         GstFormat *format,
                                                         gint64 *duration);
GstQuery*           gst_query_new_latency               (void);
void                gst_query_parse_latency             (GstQuery *query,
                                                         gboolean *live,
                                                         GstClockTime *min_latency,
                                                         GstClockTime *max_latency);
void                gst_query_set_latency               (GstQuery *query,
                                                         gboolean live,
                                                         GstClockTime min_latency,
                                                         GstClockTime max_latency);
GstQuery*           gst_query_new_seeking               (GstFormat format);
void                gst_query_set_seeking               (GstQuery *query,
                                                         GstFormat format,
                                                         gboolean seekable,
                                                         gint64 segment_start,
                                                         gint64 segment_end);
void                gst_query_parse_seeking             (GstQuery *query,
                                                         GstFormat *format,
                                                         gboolean *seekable,
                                                         gint64 *segment_start,
                                                         gint64 *segment_end);
GstQuery*           gst_query_new_formats               (void);
void                gst_query_set_formats               (GstQuery *query,
                                                         gint n_formats,
                                                         ...);
void                gst_query_set_formatsv              (GstQuery *query,
                                                         gint n_formats,
                                                         GstFormat *formats);
void                gst_query_parse_formats_length      (GstQuery *query,
                                                         guint *n_formats);
void                gst_query_parse_formats_nth         (GstQuery *query,
                                                         guint nth,
                                                         GstFormat *format);
GstQuery*           gst_query_new_segment               (GstFormat format);
void                gst_query_set_segment               (GstQuery *query,
                                                         gdouble rate,
                                                         GstFormat format,
                                                         gint64 start_value,
                                                         gint64 stop_value);
void                gst_query_parse_segment             (GstQuery *query,
                                                         gdouble *rate,
                                                         GstFormat *format,
                                                         gint64 *start_value,
                                                         gint64 *stop_value);
enum                GstBufferingMode;
GstQuery*           gst_query_new_buffering             (GstFormat format);
void                gst_query_set_buffering_percent     (GstQuery *query,
                                                         gboolean busy,
                                                         gint percent);
void                gst_query_parse_buffering_percent   (GstQuery *query,
                                                         gboolean *busy,
                                                         gint *percent);
void                gst_query_set_buffering_stats       (GstQuery *query,
                                                         GstBufferingMode mode,
                                                         gint avg_in,
                                                         gint avg_out,
                                                         gint64 buffering_left);
void                gst_query_parse_buffering_stats     (GstQuery *query,
                                                         GstBufferingMode *mode,
                                                         gint *avg_in,
                                                         gint *avg_out,
                                                         gint64 *buffering_left);
void                gst_query_set_buffering_range       (GstQuery *query,
                                                         GstFormat format,
                                                         gint64 start,
                                                         gint64 stop,
                                                         gint64 estimated_total);
void                gst_query_parse_buffering_range     (GstQuery *query,
                                                         GstFormat *format,
                                                         gint64 *start,
                                                         gint64 *stop,
                                                         gint64 *estimated_total);
GstQuery functions are used to register a new query types to the gstreamer core. Query types can be used to perform queries on pads and elements.
Queries can be created using the gst_query_new_xxx() functions.  
Query values can be set using gst_query_set_xxx(), and parsed using 
gst_query_parse_xxx() helpers.
The following example shows how to query the duration of a pipeline:
Example 13. Query duration on a pipeline
 GstQuery *query;
 gboolean res;
 query = gst_query_new_duration (GST_FORMAT_TIME);
 res = gst_element_query (pipeline, query);
 if (res) {
   gint64 duration;
   gst_query_parse_duration (query, NULL, &duration);
   g_print ("duration = %"GST_TIME_FORMAT, GST_TIME_ARGS (duration));
 }
 else {
   g_print ("duration query failed...");
 }
 gst_query_unref (query);
 
Last reviewed on 2006-02-14 (0.10.4)
typedef struct {
  GstMiniObject mini_object;
  GstQueryType type;
  GstStructure *structure;
} GstQuery;
The GstQuery structure.
| GstMiniObject  | The parent GstMiniObject type | 
| GstQueryType  | the GstQueryType | 
| GstStructure * | the GstStructure containing the query details. | 
typedef enum {
  GST_QUERY_NONE = 0,
  GST_QUERY_POSITION,
  GST_QUERY_DURATION,
  GST_QUERY_LATENCY,
  GST_QUERY_JITTER, 	/* not in draft-query, necessary? */
  GST_QUERY_RATE,
  GST_QUERY_SEEKING,
  GST_QUERY_SEGMENT,
  GST_QUERY_CONVERT,
  GST_QUERY_FORMATS,
  GST_QUERY_BUFFERING
} GstQueryType;
Standard predefined Query types
| invalid query type | |
| current position in stream | |
| total duration of the stream | |
| latency of stream | |
| current jitter of stream | |
| current rate of the stream | |
| seeking capabilities | |
| segment start/stop positions | |
| convert values between formats | |
| query supported formats for convert | |
| query available media for efficient seeking. Since 0.10.20. | 
#define GST_QUERY_TYPE(query) (((GstQuery*)(query))->type)
Get the GstQueryType of the query.
| 
 | the query to query | 
#define GST_QUERY_TYPE_NAME(query) (gst_query_type_get_name(GST_QUERY_TYPE(query)))
Get a constant string representation of the GstQueryType of the query.
| 
 | the query to query | 
Since 0.10.4
typedef struct {
  GstQueryType   value;
  gchar  	*nick;
  gchar  	*description;
  GQuark         quark;
} GstQueryTypeDefinition;
A Query Type definition
| GstQueryType  | the unique id of the Query type | 
| gchar * | a short nick | 
| gchar * | a longer description of the query type | 
| GQuark  | the quark for the nick | 
const gchar* gst_query_type_get_name (GstQueryType query);
Get a printable name for the given query type. Do not modify or free.
| 
 | the query type | 
| Returns : | a reference to the static name of the query. | 
GQuark gst_query_type_to_quark (GstQueryType query);
Get the unique quark for the given query type.
| 
 | the query type | 
| Returns : | the quark associated with the query type | 
GstQueryType gst_query_type_register (const gchar *nick, const gchar *description);
Create a new GstQueryType based on the nick or return an already registered query with that nick
| 
 | The nick of the new query | 
| 
 | The description of the new query | 
| Returns : | A new GstQueryType or an already registered query with the same nick. | 
GstQueryType gst_query_type_get_by_nick (const gchar *nick);
Get the query type registered with nick.
| 
 | The nick of the query | 
| Returns : | The query registered with nickor GST_QUERY_NONE
if the query was not registered. | 
gboolean gst_query_types_contains (const GstQueryType *types, GstQueryType type);
See if the given GstQueryType is inside the types query types array.
| 
 | The query array to search | 
| 
 | the GstQueryType to find | 
| Returns : | TRUE if the type is found inside the array | 
const GstQueryTypeDefinition* gst_query_type_get_details (GstQueryType type);
Get details about the given GstQueryType.
| 
 | a GstQueryType | 
| Returns : | The GstQueryTypeDefinition for typeor NULL on failure. | 
GstIterator* gst_query_type_iterate_definitions (void);
Get a GstIterator of all the registered query types. The definitions iterated over are read only.
| Returns : | A GstIterator of GstQueryTypeDefinition. | 
#define gst_query_ref(q) GST_QUERY (gst_mini_object_ref (GST_MINI_OBJECT (q)))
Increases the refcount of the given query by one.
| 
 | a GstQuery to increase the refcount of. | 
#define gst_query_unref(q) gst_mini_object_unref (GST_MINI_OBJECT (q))
Decreases the refcount of the query. If the refcount reaches 0, the query will be freed.
| 
 | a GstQuery to decrease the refcount of. | 
#define gst_query_copy(q) GST_QUERY (gst_mini_object_copy (GST_MINI_OBJECT (q)))
Copies the given query using the copy function of the parent GstData structure.
| 
 | a GstQuery to copy. | 
#define gst_query_make_writable(q) GST_QUERY (gst_mini_object_make_writable (GST_MINI_OBJECT (q)))
Makes a writable query from the given query.
| 
 | a GstQuery to make writable | 
GstQuery* gst_query_new_application (GstQueryType type, GstStructure *structure);
Constructs a new custom application query object. Use gst_query_unref()
when done with it.
| 
 | the query type | 
| 
 | a structure for the query | 
| Returns : | a GstQuery | 
GstStructure* gst_query_get_structure (GstQuery *query);
Get the structure of a query.
| 
 | a GstQuery | 
| Returns : | The GstStructure of the query. The structure is still owned by the query and will therefore be freed when the query is unreffed. | 
GstQuery* gst_query_new_convert (GstFormat src_format, gint64 value, GstFormat dest_format);
Constructs a new convert query object. Use gst_query_unref()
when done with it. A convert query is used to ask for a conversion between
one format and another.
void gst_query_set_convert (GstQuery *query, GstFormat src_format, gint64 src_value, GstFormat dest_format, gint64 dest_value);
Answer a convert query by setting the requested values.
void gst_query_parse_convert (GstQuery *query, GstFormat *src_format, gint64 *src_value, GstFormat *dest_format, gint64 *dest_value);
Parse a convert query answer. Any of src_format, src_value, dest_format,
and dest_value may be NULL, in which case that value is omitted.
GstQuery* gst_query_new_position (GstFormat format);
Constructs a new query stream position query object. Use gst_query_unref()
when done with it. A position query is used to query the current position
of playback in the streams, in some format.
void gst_query_set_position (GstQuery *query, GstFormat format, gint64 cur);
Answer a position query by setting the requested value in the given format.
void gst_query_parse_position (GstQuery *query, GstFormat *format, gint64 *cur);
Parse a position query, writing the format into format, and the position
into cur, if the respective parameters are non-NULL.
GstQuery* gst_query_new_duration (GstFormat format);
Constructs a new stream duration query object to query in the given format. 
Use gst_query_unref() when done with it. A duration query will give the
total length of the stream.
void gst_query_set_duration (GstQuery *query, GstFormat format, gint64 duration);
Answer a duration query by setting the requested value in the given format.
void gst_query_parse_duration (GstQuery *query, GstFormat *format, gint64 *duration);
Parse a duration query answer. Write the format of the duration into format,
and the value into duration, if the respective variables are non-NULL.
GstQuery* gst_query_new_latency (void);
Constructs a new latency query object. 
Use gst_query_unref() when done with it. A latency query is usually performed
by sinks to compensate for additional latency introduced by elements in the
pipeline.
| Returns : | A GstQuery | 
Since 0.10.12
void gst_query_parse_latency (GstQuery *query, gboolean *live, GstClockTime *min_latency, GstClockTime *max_latency);
Parse a latency query answer.
| 
 | a GstQuery | 
| 
 | storage for live or NULL | 
| 
 | the storage for the min latency or NULL | 
| 
 | the storage for the max latency or NULL | 
Since 0.10.12
void gst_query_set_latency (GstQuery *query, gboolean live, GstClockTime min_latency, GstClockTime max_latency);
Answer a latency query by setting the requested values in the given format.
| 
 | a GstQuery | 
| 
 | if there is a live element upstream | 
| 
 | the minimal latency of the live element | 
| 
 | the maximal latency of the live element | 
Since 0.10.12
GstQuery* gst_query_new_seeking (GstFormat format);
Constructs a new query object for querying seeking properties of the stream.
void gst_query_set_seeking (GstQuery *query, GstFormat format, gboolean seekable, gint64 segment_start, gint64 segment_end);
Set the seeking query result fields in query.
| 
 | a GstQuery | 
| 
 | the format to set for the segment_startandsegment_endvalues | 
| 
 | the seekable flag to set | 
| 
 | the segment_start to set | 
| 
 | the segment_end to set | 
void gst_query_parse_seeking (GstQuery *query, GstFormat *format, gboolean *seekable, gint64 *segment_start, gint64 *segment_end);
Parse a seeking query, writing the format into format, and 
other results into the passed parameters, if the respective parameters
are non-NULL
| 
 | a GST_QUERY_SEEKING type query GstQuery | 
| 
 | the format to set for the segment_startandsegment_endvalues | 
| 
 | the seekable flag to set | 
| 
 | the segment_start to set | 
| 
 | the segment_end to set | 
GstQuery* gst_query_new_formats (void);
Constructs a new query object for querying formats of the stream.
| Returns : | A GstQuery | 
Since 0.10.4
void gst_query_set_formats (GstQuery *query, gint n_formats, ...);
Set the formats query result fields in query. The number of formats passed
must be equal to n_formats.
| 
 | a GstQuery | 
| 
 | the number of formats to set. | 
| 
 | A number of GstFormatsequal ton_formats. | 
void gst_query_set_formatsv (GstQuery *query, gint n_formats, GstFormat *formats);
Set the formats query result fields in query. The number of formats passed
in the formats array must be equal to n_formats.
| 
 | a GstQuery | 
| 
 | the number of formats to set. | 
| 
 | An array containing n_formatsGstFormatvalues. | 
Since 0.10.4
void gst_query_parse_formats_length (GstQuery *query, guint *n_formats);
Parse the number of formats in the formats query.
| 
 | a GstQuery | 
| 
 | the number of formats in this query. | 
Since 0.10.4
void gst_query_parse_formats_nth (GstQuery *query, guint nth, GstFormat *format);
Parse the format query and retrieve the nth format from it into 
format. If the list contains less elements than nth, format will be
set to GST_FORMAT_UNDEFINED.
| 
 | a GstQuery | 
| 
 | the nth format to retrieve. | 
| 
 | a pointer to store the nth format | 
Since 0.10.4
GstQuery* gst_query_new_segment (GstFormat format);
Constructs a new segment query object. Use gst_query_unref()
when done with it. A segment query is used to discover information about the
currently configured segment for playback.
void gst_query_set_segment (GstQuery *query, gdouble rate, GstFormat format, gint64 start_value, gint64 stop_value);
Answer a segment query by setting the requested values. The normal playback segment of a pipeline is 0 to duration at the default rate of 1.0. If a seek was performed on the pipeline to play a different segment, this query will return the range specified in the last seek.
start_value and stop_value will respectively contain the configured 
playback range start and stop values expressed in format. 
The values are always between 0 and the duration of the media and 
start_value <= stop_value. rate will contain the playback rate. For
negative rates, playback will actually happen from stop_value to
start_value.
void gst_query_parse_segment (GstQuery *query, gdouble *rate, GstFormat *format, gint64 *start_value, gint64 *stop_value);
Parse a segment query answer. Any of rate, format, start_value, and 
stop_value may be NULL, which will cause this value to be omitted.
See gst_query_set_segment() for an explanation of the function arguments.
typedef enum {
  GST_BUFFERING_STREAM,
  GST_BUFFERING_DOWNLOAD,
  GST_BUFFERING_TIMESHIFT,
  GST_BUFFERING_LIVE
} GstBufferingMode;
The different types of buffering methods.
GstQuery* gst_query_new_buffering (GstFormat format);
Constructs a new query object for querying the buffering status of a stream.
Since 0.10.20
void gst_query_set_buffering_percent (GstQuery *query, gboolean busy, gint percent);
Set the percentage of buffered data. This is a value between 0 and 100.
The busy indicator is TRUE when the buffering is in progress.
| 
 | A valid GstQuery of type GST_QUERY_BUFFERING. | 
| 
 | if buffering is busy | 
| 
 | a buffering percent | 
Since 0.10.20
void gst_query_parse_buffering_percent (GstQuery *query, gboolean *busy, gint *percent);
Get the percentage of buffered data. This is a value between 0 and 100.
The busy indicator is TRUE when the buffering is in progress.
| 
 | A valid GstQuery of type GST_QUERY_BUFFERING. | 
| 
 | if buffering is busy | 
| 
 | a buffering percent | 
Since 0.10.20
void gst_query_set_buffering_stats (GstQuery *query, GstBufferingMode mode, gint avg_in, gint avg_out, gint64 buffering_left);
Configures the buffering stats values in query.
| 
 | A valid GstQuery of type GST_QUERY_BUFFERING. | 
| 
 | a buffering mode | 
| 
 | the average input rate | 
| 
 | the average output rate | 
| 
 | amount of buffering time left | 
Since 0.10.20
void gst_query_parse_buffering_stats (GstQuery *query, GstBufferingMode *mode, gint *avg_in, gint *avg_out, gint64 *buffering_left);
Extracts the buffering stats values from query.
| 
 | A valid GstQuery of type GST_QUERY_BUFFERING. | 
| 
 | a buffering mode | 
| 
 | the average input rate | 
| 
 | the average output rate | 
| 
 | amount of buffering time left | 
Since 0.10.20
void gst_query_set_buffering_range (GstQuery *query, GstFormat format, gint64 start, gint64 stop, gint64 estimated_total);
Set the available query result fields in query.
| 
 | a GstQuery | 
| 
 | the format to set for the startandstopvalues | 
| 
 | the start to set | 
| 
 | the stop to set | 
| 
 | estimated total amount of download time | 
Since 0.10.20
void gst_query_parse_buffering_range (GstQuery *query, GstFormat *format, gint64 *start, gint64 *stop, gint64 *estimated_total);
Parse an available query, writing the format into format, and 
other results into the passed parameters, if the respective parameters
are non-NULL
| 
 | a GST_QUERY_SEEKING type query GstQuery | 
| 
 | the format to set for the segment_startandsegment_endvalues | 
| 
 | the start to set | 
| 
 | the stop to set | 
| 
 | estimated total amount of download time | 
Since 0.10.20