Searching the SDP Session Structure

The functions in this section search the SDP session structure for specific values and return pointers to those values.

Finding an Attribute in an SDP Session Structure

sdp_attr_t *sdp_find_attribute(sdp_attr_t *attr, const char *name);

The sdp_find_attribute() function searches the attribute list that is specified by the attr parameter for the attribute name that is specified by the name parameter.

Return Values: The sdp_find_attribute() function returns a pointer to the attribute (sdp_attr_t *) that is specified by the name parameter when the function completes successfully. In all other cases, the sdp_find_attribute() function returns a value of NULL.

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Example 3–2 Using the sdp_find_attribute() Function

The incomplete SDP description in this example has an audio section.

m=audio 49170 RTP/AVP 0 8
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=sendonly
a=ptime:10000
a=maxptime:20000

/*
* Assuming that above description is parsed using sdp_parse and that
* the parsed structure is in "session" sdp_session_t structure.
*/

sdp_attr_t *ptime;
sdp_attr_t *max_ptime;
sdp_media_t *media = session->s_media;

if ((ptime = sdp_find_attribute(media->m_attr, "ptime")) == NULL)
/* ptime attribute not present */
else if((max_ptime = sdp_find_attribute(media->m_attr,
 "maxptime")) == NULL)
/* max_ptime attribute not present */

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Finding Media in an SDP Session Structure

sdp_media_t *sdp_find_media(sdp_media_t *media, const char *name);

The sdp_find_media() function searches the media list that is specified by the media parameter for the media entry that is specified by the name parameter.

Return Values: The sdp_find_media() function returns a pointer to the media list entry (sdp_media_t *) that is specified by the name parameter when the function completes successfully. In all other cases, the sdp_find_media() function returns a value of NULL.

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Example 3–3 Using the sdp_find_media() Function

The incomplete SDP description in this example has two sections, an audio section and a video section.

m=audio 49170 RTP/AVP 0 8
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
m=video 51372 RTP/AVP 31 32
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000

/*
* Assuming that above description is parsed using sdp_parse() and that
* the parsed structure is in "session" sdp_session_t structure.
*/

sdp_media_t     *my_media;
my_media = sdp_find_media(session->s_media, "video");

/*
* my_media now points to the structure containg video media section
* information
*/

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Finding a Media Format in an SDP Session Structure

sdp_attr_t *sdp_find_media_rtpmap(sdp_media_t *media, const char *format);

The sdp_find_media_rtpmap() function searches the attribute list of the media structure that is specified by the media parameter for the format entry that is specified by the format parameter.

Return Values: The sdp_find_media_rtpmap() function returns a pointer to the format entry (sdp_attr_t *) that is specified by the name parameter when the function completes successfully. In all other cases, the sdp_find_media() function returns a value of NULL.

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Example 3–4 Using the sdp_find_media_rtpmap() Function

The incomplete SDP description in this example has two sections, an audio section and a video section.

m=audio 49170 RTP/AVP 0 8
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
m=video 51372 RTP/AVP 31 32
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000

/*
* Assuming that above description is parsed using sdp_parse() and that
* the parsed structure is in "session" sdp_session_t structure.
*/

sdp_media_t     *video;
sdp_attr_t      *mpv;

video = sdp_find_media(session->s_media, "video);
mpv = sdp_find_media_rtpmap(video, "32");

/*
* Now the attribute structure sdp_attr_t, mpv will be having
* values from the attribute field "a=rtpmap:32 MPV/90000"
*/

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