Class MediaDescription

Class for processing the Media Description "m=" type for the SDP contents. See Section 5.14 of RFC 8866.

Inheritance

object

MediaDescription

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

Namespace: SipLib.Sdp

Assembly: SipLib.dll

Syntax

public class MediaDescription

Constructors

MediaDescription()

Constructs an empty MediaDescription object. Use this constructor to create a new Media Description for a new SDP message block to send.

Declaration

public MediaDescription()

MediaDescription(string, int, List<int>)

Constructs a new MediaDescription object from parameters provided by the caller.

Declaration

public MediaDescription(string strMediaType, int iPort, List<int> payloadTypes)

Parameters

Type	Name	Description
string	strMediaType	Media type. Ex: "audio" or "video"
int	iPort	Port number that the session will occur on.
List<int>	payloadTypes	Media payload types.

Properties

Attributes

Contains the attributes for this type of media except the rtpmap attributes, which are stored in the RtpMapAttributes field.

Declaration

public List<SdpAttribute> Attributes { get; set; }

Property Value

Type	Description
List<SdpAttribute>

Bandwidth

Specifies the bandwidth limit for the media in kilo-bits per second. This is comes from or generates a b=AS:Bandwidth line in the media description. An empty or null value indicates that there is no b= line in the media description.

Declaration

public string Bandwidth { get; set; }

Property Value

Type	Description
string

ConnectionData

Contains the connection data (c=) for this media. If null, then use the ConnectionData of the SDP session.

Declaration

public ConnectionData? ConnectionData { get; set; }

Property Value

Type	Description
ConnectionData

Label

Gets or sets the label attribute of a media description block. RFC 4574 specifies the characteristics of the label attribute.

The getter returns an empty string if the media description does not have a label attribute. The setter removes any existing label attributes and then adds one with the value to ensure that each MediaDescription has a single label attribute.

Declaration

public string? Label { get; set; }

Property Value

Type	Description
string

MediaDirection

Gets or Sets the media direction attribute for this media description. If there is no media direction attribute, then the getter returns sendrecv.

Declaration

public MediaDirectionEnum MediaDirection { get; set; }

Property Value

Type	Description
MediaDirectionEnum

MediaType

Specifies the media type. Example: "audio", "video", "text" or "message".

Declaration

public string MediaType { get; set; }

Property Value

Type	Description
string

PayloadTypes

Contains a list of payload types for the m= line.

Declaration

public List<int> PayloadTypes { get; set; }

Property Value

Type	Description
List<int>

Port

Specifies the TCP/UDP port number;

Declaration

public int Port { get; set; }

Property Value

Type	Description
int

RtpMapAttributes

Contains a list of RtpMap objects. Each object corresponds to a a=rtpmap .... line in the media description.

Declaration

public List<RtpMapAttribute> RtpMapAttributes { get; set; }

Property Value

Type	Description
List<RtpMapAttribute>

Transport

Specifies the transport mechanism: "TCP", "UDP", "RTP/AVP", etc.

Declaration

public string Transport { get; set; }

Property Value

Type	Description
string

UsingEncryption

Returns true if this MediaDescription object calls for DTLS-SRTP or SDES-SRTP encryption or false if it does not.

Declaration

public bool UsingEncryption { get; }

Property Value

Type	Description
bool

Methods

AddSetupAttribute(SetupType)

Adds a a=setup:xxx attribute.

Declaration

public void AddSetupAttribute(SetupType SetType)

Parameters

Type	Name	Description
SetupType	SetType	Specifies the role (active, passive, etc.)

AreEqual(Sdp, MediaDescription, Sdp, MediaDescription)

Compares two MediaDescription objects to determine if they are equal.

Declaration

public static bool AreEqual(Sdp sdp1, MediaDescription md1, Sdp sdp2, MediaDescription md2)

Parameters

Type	Name	Description
Sdp	sdp1	The Sdp object that contains the first MediaDescription object (md1).
MediaDescription	md1	The first MediaDescription object. Must be contained in sdp1.
Sdp	sdp2	The Sdp object that contains the second MediaDescription object (md2).
MediaDescription	md2	The second MediaDescription object. Must be contained in sdp2.

Returns

Type	Description
bool	Returns true if the two MediaDescription objects are equal.

Remarks

This method uses the two Sdp objects because the connection information (c=) may be in the session level (i.e., in the Sdp object) or media description level (i.e., in the MediaDescription object).

The two MediaDescription objects must be for the same type of media.

BuildH264AnswerSmd(int)

Builds an MediaDescription that contains only the offerred H264 codec attributes.

Declaration

public MediaDescription? BuildH264AnswerSmd(int Port)

Parameters

Type	Name	Description
int	Port	RTP port number to use.

Returns

Type	Description
MediaDescription	Returns a new MediaDescription object or null if the video media block does not contain an offer of H264 media.

CreateCopy()

Creates a deep copy of this object.

Declaration

public MediaDescription CreateCopy()

Returns

Type	Description
MediaDescription	Returns a new object with a copy of each member variable in this object.

GetAttributeValue(string)

Gets the attribute value for the specified attribute name.

Declaration

public string? GetAttributeValue(string strAttributeName)

Parameters

Type	Name	Description
string	strAttributeName	Name of the attribute to search for.

Returns

Type	Description
string	A string containing the attribute value. Returns an empty string if the attribute name was not found or if the attribute was found but does not have a value (not all attributes have values).

GetCryptoAttributes()

Gets a list of the CryptoAttributes in this MediaDescription.

Declaration

public List<CryptoAttribute> GetCryptoAttributes()

Returns

Type	Description
List<CryptoAttribute>	Returns a list of the crypto attributes for SDES-SRTP in this MediaDescription. The return value will not be null but it may be empty.

GetFmtpForFormatNumber(string)

Finds the fmtp attribute for the specified media format number.

Declaration

public SdpAttribute? GetFmtpForFormatNumber(string strFormatNumber)

Parameters

Type	Name	Description
string	strFormatNumber	String representation of the media format number to look for.

Returns

Type	Description
SdpAttribute	Returns the SdpAttribute object or null if its not found.

GetNamedAttribute(string)

Returns the SdpAttribute object for a named attribute.

Declaration

public SdpAttribute? GetNamedAttribute(string strAttr)

Parameters

Type	Name	Description
string	strAttr	Name of the attribute to search for.

Returns

Type	Description
SdpAttribute	Returns a SdpAttribute for the named attribute if it is found or null if the named attribute is not present.

GetNamedAttributes(string)

Gets a list of SdpAttributes for an attribute name.

Declaration

public List<SdpAttribute> GetNamedAttributes(string strAttr)

Parameters

Type	Name	Description
string	strAttr	Attribute name.

Returns

Type	Description
List<SdpAttribute>	Returns a list of SdpAttribute object. The return value will never be null but will be empty if there are no attributes with a name that matches the strAttr parameter.

GetRtpMapForCodecType(string)

Finds the RtpMapAttribute object for the specified codec name (encoding name)

Declaration

public RtpMapAttribute? GetRtpMapForCodecType(string strCodecName)

Parameters

Type	Name	Description
string	strCodecName	Codec or encoding name

Returns

Type	Description
RtpMapAttribute	Returns the RtpMapAttribute object if found or null if not found

GetRtpMapForPayloadType(int)

Gets the RtpMapAttribute object for the specified payload type

Declaration

public RtpMapAttribute? GetRtpMapForPayloadType(int payloadType)

Parameters

Type	Name	Description
int	payloadType	Specifies the payload type to look for

Returns

Type	Description
RtpMapAttribute	Returns the RtpMapAttribute object if successful or null if it is not present

GetSetupTypeAttributeValue()

Gets the value of the setup attribute.

Declaration

public SetupType GetSetupTypeAttributeValue()

Returns

Type	Description
SetupType

GetTelephoneEventPayloadType(out int)

Retrieves the payload type for DTMF telephone events.

Declaration

public bool GetTelephoneEventPayloadType(out int PayloadType)

Parameters

Type	Name	Description
int	PayloadType	Output is set to the value for the first rtpmap attribute for a telephone-event if the return value is true. This output parameter will be set to 0 if the return value of this function is false.

Returns

Type	Description
bool	True if the rtpmap attribute for a telephone-event is found. A return value of false indicates that the telephone-event rtpmap attrubute could not be found.

HasMediaStateAttribute()

Determines if the media description has an attribute that specifies the media state. The media state attributes are inactive, sendrecv, recvonly and sendonly.

Declaration

public bool HasMediaStateAttribute()

Returns

Type	Description
bool	Returns true if there is a media state attribute, else returns false.

ParseMediaDescriptionLine(string)

Parses a string containing the parameter fields of a SDP m= line

Declaration

public static MediaDescription ParseMediaDescriptionLine(string strMd)

Parameters

Type	Name	Description
string	strMd	Contains the parameter fields of a m= line. The m= field must not be included.

Returns

Type	Description
MediaDescription	Returns a new MediaDescription object.

ParseMediaDescriptionString(string)

Parses a string containing a full media description block into a MediaDescription object.

Declaration

public static MediaDescription? ParseMediaDescriptionString(string strMd)

Parameters

Type	Name	Description
string	strMd	Input string containing the lines of an SDP media description block. The first line must contain an m= line

Returns

Type	Description
MediaDescription	Returns a new MediaDescription object of successful or null if an error is detected.

RemoveNamedAttributes(string)

Removes all instances of a named SDP attribute.

Declaration

public void RemoveNamedAttributes(string Attr)

Parameters

Type	Name	Description
string	Attr	Name of the SDP attribute to remove.

ToString()

Converts the MediaDescription object to a string.

Declaration

public override string ToString()

Returns

Type	Description
string	The string format is: "m=MediaType Port Transport MediaFormat(s)"

Overrides

object.ToString()

UsingDtlsSrtp(out SetupType)

Determines if its necessary to use DTLS-SRTP to negotiate encryption keys and algorithms.

Declaration

public bool UsingDtlsSrtp(out SetupType SetType)

Parameters

Type	Name	Description
SetupType	SetType	SetupType to use in the answer to the offered SetupType.

Returns

Type	Description
bool	Returns true if DTLS-SRTP is required.

UsingSdesSrtp()

Returns true if this MediaDescription object is for SDES-SRTP media encryption.

Declaration

public bool UsingSdesSrtp()

Returns

Type	Description
bool