path: root/spec/Channel_Type_Streamed_Media.xml

<?xml version="1.0" ?>
<node name="/Channel_Type_Streamed_Media" xmlns:tp="http://telepathy.freedesktop.org/wiki/DbusSpec#extensions-v0">
  <tp:copyright> Copyright © 2005-2009 Collabora Limited </tp:copyright>
  <tp:copyright> Copyright © 2005-2009 Nokia Corporation </tp:copyright>
  <tp:copyright> Copyright © 2006 INdT </tp:copyright>
  <tp:license xmlns="http://www.w3.org/1999/xhtml">
    <p>This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.</p>

<p>This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.</p>

<p>You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.</p>
  </tp:license>
  <interface name="org.freedesktop.Telepathy.Channel.Type.StreamedMedia">
    <tp:requires interface="org.freedesktop.Telepathy.Channel"/>
    <tp:requires interface="org.freedesktop.Telepathy.Channel.Interface.Group"/>

    <tp:enum name="Media_Stream_Type" type="u"
      array-name="Media_Stream_Type_List">
      <tp:enumvalue suffix="Audio" value="0">
        <tp:docstring>An audio stream</tp:docstring>
      </tp:enumvalue>
      <tp:enumvalue suffix="Video" value="1">
        <tp:docstring>A video stream</tp:docstring>
      </tp:enumvalue>
    </tp:enum>

    <tp:enum name="Media_Stream_State" type="u">
      <tp:enumvalue suffix="Disconnected" value="0">
        <tp:docstring>The stream is disconnected.</tp:docstring>
      </tp:enumvalue>
      <tp:enumvalue suffix="Connecting" value="1">
        <tp:docstring>The stream is trying to connect.</tp:docstring>
      </tp:enumvalue>
      <tp:enumvalue suffix="Connected" value="2">
        <tp:docstring>The stream is connected.</tp:docstring>
      </tp:enumvalue>
    </tp:enum>

    <tp:enum name="Media_Stream_Direction" type="u">
      <tp:enumvalue suffix="None" value="0">
        <tp:docstring>Media are not being sent or received</tp:docstring>
      </tp:enumvalue>
      <tp:enumvalue suffix="Send" value="1">
        <tp:docstring>Media are being sent, but not received</tp:docstring>
      </tp:enumvalue>
      <tp:enumvalue suffix="Receive" value="2">
        <tp:docstring>Media are being received, but not sent</tp:docstring>
      </tp:enumvalue>
      <tp:enumvalue suffix="Bidirectional" value="3">
        <tp:docstring>Media are being sent and received</tp:docstring>
      </tp:enumvalue>
    </tp:enum>

    <tp:flags name="Media_Stream_Pending_Send" value-prefix="Media_Stream_Pending" type="u">
      <tp:flag suffix="Local_Send" value="1">
        <tp:docstring>
            The local user has been asked to send media by the remote user.
            Call <tp:member-ref>RequestStreamDirection</tp:member-ref> to
            indicate whether or not this is acceptable.
        </tp:docstring>
      </tp:flag>
      <tp:flag suffix="Remote_Send" value="2">
        <tp:docstring>
            The remote user has been asked to send media by the local user.
            The <tp:member-ref>StreamDirectionChanged</tp:member-ref> signal
            will be emitted when the remote user accepts or rejects this
            change.
        </tp:docstring>
      </tp:flag>
    </tp:flags>

    <tp:struct name="Media_Stream_Info" array-name="Media_Stream_Info_List">
      <tp:member type="u" tp:type="Stream_ID" name="Identifier"/>
      <tp:member type="u" tp:type="Contact_Handle" name="Contact"/>
      <tp:member type="u" tp:type="Media_Stream_Type" name="Type"/>
      <tp:member type="u" tp:type="Media_Stream_State" name="State"/>
      <tp:member type="u" tp:type="Media_Stream_Direction" name="Direction"/>
      <tp:member type="u" tp:type="Media_Stream_Pending_Send"
        name="Pending_Send_Flags"/>
    </tp:struct>

    <tp:simple-type name="Stream_ID" type="u"
      array-name="Stream_ID_List">
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>An unsigned integer identifying a stream within a channel.</p>
      </tp:docstring>
    </tp:simple-type>

    <method name="ListStreams" tp:name-for-bindings="List_Streams">
      <arg direction="out" type="a(uuuuuu)" tp:type="Media_Stream_Info[]"
        name="Streams">
        <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
          An array of structs containing:
          <ul>
          <li>the stream identifier</li>
          <li>the contact handle who the stream is with (or 0 if the stream
            represents more than a single member)</li>
          <li>the type of the stream</li>
          <li>the current stream state</li>
          <li>the current direction of the stream</li>
          <li>the current pending send flags</li>
          </ul>
        </tp:docstring>
      </arg>
      <tp:docstring>
        Returns an array of structs representing the streams currently active
        within this channel. Each stream is identified by an unsigned integer
        which is unique for each stream within the channel.
      </tp:docstring>
    </method>

    <method name="RemoveStreams" tp:name-for-bindings="Remove_Streams">
      <arg direction="in" name="Streams" type="au" tp:type="Stream_ID[]">
        <tp:docstring>
          An array of stream identifiers (as defined in
          <tp:member-ref>ListStreams</tp:member-ref>)
        </tp:docstring>
      </arg>

      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>Request that the given streams are removed. If all streams are
          removed, the channel MAY close.</p>

        <p>Clients SHOULD NOT attempt to terminate calls by removing all the
          streams; instead, clients SHOULD terminate calls by removing the
          <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel.Interface">Group.SelfHandle</tp:dbus-ref>
          from the channel, using either
          <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel.Interface.Group">RemoveMembers</tp:dbus-ref>
          or
          <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel.Interface.Group">RemoveMembersWithReason</tp:dbus-ref>.
          </p>
      </tp:docstring>

      <tp:possible-errors>
        <tp:error name="org.freedesktop.Telepathy.Error.InvalidArgument">
          <tp:docstring>
            A stream identifier is unknown
          </tp:docstring>
        </tp:error>
      </tp:possible-errors>
    </method>

    <method name="RequestStreamDirection"
      tp:name-for-bindings="Request_Stream_Direction">
      <arg direction="in" name="Stream_ID" type="u">
        <tp:docstring>
          The stream identifier (as defined in
          <tp:member-ref>ListStreams</tp:member-ref>)
        </tp:docstring>
      </arg>
      <arg direction="in" name="Stream_Direction" type="u" tp:type="Media_Stream_Direction">
        <tp:docstring>
          The desired stream direction (a value of MediaStreamDirection)
        </tp:docstring>
      </arg>
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>Request a change in the direction of an existing stream. In particular,
        this might be useful to stop sending media of a particular type,
        or inform the peer that you are no longer using media that is being
        sent to you.</p>

        <p>Depending on the protocol, streams which are no longer sending in
        either direction should be removed and a
        <tp:member-ref>StreamRemoved</tp:member-ref> signal emitted.
        Some direction changes can be enforced locally (for example,
        BIDIRECTIONAL -&gt; RECEIVE can be achieved by merely stopping sending),
        others may not be possible on some protocols, and some need agreement
        from the remote end. In this case, the MEDIA_STREAM_PENDING_REMOTE_SEND
        flag will be set in the
        <tp:member-ref>StreamDirectionChanged</tp:member-ref> signal, and the
        signal
        emitted again without the flag to indicate the resulting direction when
        the remote end has accepted or rejected the change.</p>
      </tp:docstring>
      <tp:possible-errors>
        <tp:error name="org.freedesktop.Telepathy.Error.InvalidArgument">
          <tp:docstring>
            A stream identifier is unknown
          </tp:docstring>
        </tp:error>
        <tp:error name="org.freedesktop.Telepathy.Error.NotAvailable">
          <tp:docstring>
            The requested direction is not available on this stream
          </tp:docstring>
        </tp:error>
      </tp:possible-errors>
    </method>

    <method name="RequestStreams" tp:name-for-bindings="Request_Streams">
      <arg direction="in" name="Contact_Handle" type="u" tp:type="Contact_Handle">
        <tp:docstring>
          A contact handle with whom to establish the streams
        </tp:docstring>
      </arg>
      <arg direction="in" name="Types" type="au" tp:type="Media_Stream_Type[]">
        <tp:docstring>
          An array of stream types (values of MediaStreamType)
        </tp:docstring>
      </arg>
      <arg direction="out" type="a(uuuuuu)" tp:type="Media_Stream_Info[]"
        name="Streams">
        <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
          An array of structs (in the same order as the given stream types)
          containing:
          <ul>
            <li>the stream identifier</li>
            <li>the contact handle who the stream is with (or 0 if the stream
              represents more than a single member)</li>
            <li>the type of the stream</li>
            <li>the current stream state</li>
            <li>the current direction of the stream</li>
            <li>the current pending send flags</li>
          </ul>
        </tp:docstring>
      </arg>
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>Request that streams be established to exchange the given types of
        media with the given member. In general this will try and establish a
        bidirectional stream, but on some protocols it may not be possible to
        indicate to the peer that you would like to receive media, so a
        send-only stream will be created initially. In the cases where the
        stream requires remote agreement (eg you wish to receive media from
        them), the <tp:member-ref>StreamDirectionChanged</tp:member-ref> signal
        will be emitted with the
        MEDIA_STREAM_PENDING_REMOTE_SEND flag set, and the signal emitted again
        with the flag cleared when the remote end has replied.</p>

        <p>If streams of the requested types already exist, calling this
          method results in the creation of additional streams. Accordingly,
          clients wishing to have exactly one audio stream or exactly one
          video stream SHOULD check for the current streams using
          <tp:member-ref>ListStreams</tp:member-ref> before calling this
          method.</p>
      </tp:docstring>
      <tp:changed version="0.17.2">
        <p>It is valid to use a handle which is neither
          a current nor pending member in this channel's <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Interface">Group</tp:dbus-ref>
          interface. If
          so, that handle will be added to the remote-pending set only when
          an attempt has actually been made to contact them. For further
          call-state notification, use the <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Interface">CallState</tp:dbus-ref>
          interface, if
          supported. This usage was not allowed in spec versions below
          0.17.2.</p>
      </tp:changed>
      <tp:possible-errors>
        <tp:error name="org.freedesktop.Telepathy.Error.InvalidHandle"/>
        <tp:error name="org.freedesktop.Telepathy.Error.InvalidArgument">
          <tp:docstring>
            A stream type given is invalid.
          </tp:docstring>
        </tp:error>
        <tp:error name="org.freedesktop.Telepathy.Error.NotImplemented">
          <tp:docstring>
            A stream type given is not implemented by the connection manager.
            Since 0.17.23, connection managers SHOULD raise this error
            in preference to InvalidArgument.
            <tp:rationale>
              Connection managers can't know whether an unknown number
              is a valid stream type that was introduced in a later spec
              version.
            </tp:rationale>
          </tp:docstring>
        </tp:error>
        <tp:error name="org.freedesktop.Telepathy.Error.NotAvailable">
          <tp:docstring>
            That contact's client does not implement one of the given stream
            types. For this method, clients SHOULD consider this error and
            NotCapable to be equivalent.
          </tp:docstring>
        </tp:error>
        <tp:error name="org.freedesktop.Telepathy.Error.NotCapable">
          <tp:docstring>
            That contact's client does not implement one of the given stream
            types. Since 0.17.23, connection managers SHOULD raise
            this in preference to NotAvailable.
          </tp:docstring>
        </tp:error>
      </tp:possible-errors>
    </method>

    <signal name="StreamAdded" tp:name-for-bindings="Stream_Added">
      <arg name="Stream_ID" type="u">
        <tp:docstring>
          The stream identifier (as defined in
          <tp:member-ref>ListStreams</tp:member-ref>)
        </tp:docstring>
      </arg>
      <arg name="Contact_Handle" type="u" tp:type="Contact_Handle">
        <tp:docstring>
          The contact handle who the stream is with (or 0 if it
          represents more than a single member)
        </tp:docstring>
      </arg>
      <arg name="Stream_Type" type="u" tp:type="Media_Stream_Type">
        <tp:docstring>
          The stream type (a value from MediaStreamType)
        </tp:docstring>
      </arg>
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>Emitted when a new stream has been added to this channel.
          Clients SHOULD assume that the stream's
          <tp:type>Media_Stream_State</tp:type> is initially Disconnected.</p>

        <p>If a connection manager needs to represent the addition of a stream
          whose state is already Connecting or Connected, it MUST do this
          by emitting StreamAdded, closely followed by
          <tp:member-ref>StreamStateChanged</tp:member-ref> indicating a
          change to the appropriate state.</p>

        <tp:rationale>
          <p>Historically, it was not clear from the StreamAdded signal what
            the state of the stream was. telepathy-spec 0.17.22
            clarified this.</p>
        </tp:rationale>

        <p>Similarly, clients SHOULD assume that the initial
          <tp:type>Media_Stream_Direction</tp:type> of a newly added stream
          is Receive, and that the initial
          <tp:type>Media_Stream_Pending_Send</tp:type> is
          Pending_Local_Send.</p>

        <p>If a connection manager needs to represent the addition of a stream
          whose direction or pending-send differs from those initial values,
          it MUST do so by emitting StreamAdded, closely followed by
          <tp:member-ref>StreamDirectionChanged</tp:member-ref> indicating a
          change to the appropriate direction and pending-send state.</p>

        <tp:rationale>
          <p>StreamAdded doesn't itself indicate the stream's direction; this
            is unfortunate, but is preserved for compatibility.</p>

          <p>This is the appropriate direction for streams added by a remote
            contact on existing connection managers, and does not violate
            user privacy by automatically sending audio or video (audio streams
            start off muted, video streams start off not sending). For
            streams added by the local user using the client receiving the
            signal, the true direction can also be determined from the return
            value of the <tp:member-ref>RequestStreams</tp:member-ref>
            method.</p>

          <p>Existing clients typically operate by maintaining a separate
            idea of the directions that they would like the streams to have,
            and enforcing these intended directions by calling
            <tp:member-ref>RequestStreamDirection</tp:member-ref> whenever
            needed.</p>
        </tp:rationale>
      </tp:docstring>
    </signal>

    <signal name="StreamDirectionChanged"
      tp:name-for-bindings="Stream_Direction_Changed">
      <arg name="Stream_ID" type="u">
        <tp:docstring>
        The stream identifier (as defined in <tp:member-ref>ListStreams</tp:member-ref>)
        </tp:docstring>
      </arg>
      <arg name="Stream_Direction" type="u" tp:type="Media_Stream_Direction">
        <tp:docstring>
        The new stream direction (as defined in ListStreams)
        </tp:docstring>
      </arg>
      <arg name="Pending_Flags" type="u" tp:type="Media_Stream_Pending_Send">
        <tp:docstring>
        The new pending send flags (as defined in ListStreams)
        </tp:docstring>
      </arg>
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>Emitted when the direction or pending flags of a stream are
          changed.</p>

        <p>If the MEDIA_STREAM_PENDING_LOCAL_SEND flag is set, the remote user
          has requested that we begin sending on this stream.
          <tp:member-ref>RequestStreamDirection</tp:member-ref>
          should be called to indicate whether or not this change is
          acceptable.</p>

        <tp:rationale>
          <p>This allows for a MSN-style user interface, "Fred has asked you
            to enable your webcam. (Accept | Reject)", if desired.</p>
        </tp:rationale>
      </tp:docstring>
    </signal>

    <signal name="StreamError" tp:name-for-bindings="Stream_Error">
      <arg name="Stream_ID" type="u">
        <tp:docstring>
        The stream identifier (as defined in
        <tp:member-ref>ListStreams</tp:member-ref>)
        </tp:docstring>
      </arg>
      <arg name="Error_Code" type="u" tp:type="Media_Stream_Error">
        <tp:docstring>
          A stream error number, one of the values of MediaStreamError
        </tp:docstring>
      </arg>
      <arg name="Message" type="s">
        <tp:docstring>
          A string describing the error (for debugging purposes only)
        </tp:docstring>
      </arg>
      <tp:docstring>
        Emitted when a stream encounters an error.
      </tp:docstring>
    </signal>

    <signal name="StreamRemoved" tp:name-for-bindings="Stream_Removed">
      <arg name="Stream_ID" type="u">
        <tp:docstring>
        stream_id - the stream identifier (as defined in
        <tp:member-ref>ListStreams</tp:member-ref>)
        </tp:docstring>
      </arg>
      <tp:docstring>
        Emitted when a stream has been removed from this channel.
      </tp:docstring>
    </signal>

    <signal name="StreamStateChanged"
      tp:name-for-bindings="Stream_State_Changed">
      <arg name="Stream_ID" type="u">
        <tp:docstring>
          The stream identifier (as defined in
          <tp:member-ref>ListStreams</tp:member-ref>)
        </tp:docstring>
      </arg>
      <arg name="Stream_State" type="u" tp:type="Media_Stream_State">
        <tp:docstring>
          The new stream state (as defined in ListStreams)
        </tp:docstring>
      </arg>
      <tp:docstring>
        Emitted when a member's stream's state changes.
      </tp:docstring>
    </signal>

    <property name="InitialAudio" tp:name-for-bindings="Initial_Audio"
      type="b" access="read">
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>If set to true in a channel request that will create a new channel,
          the connection manager should immediately attempt to establish an
          audio stream to the remote contact, making it unnecessary for the
          client to call <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel.Type.StreamedMedia">RequestStreams</tp:dbus-ref>.</p>

        <p>If this property, or InitialVideo, is passed to EnsureChannel
          (as opposed to CreateChannel), the connection manager SHOULD ignore
          these properties when checking whether it can return an existing
          channel as suitable; these properties only become significant when
          the connection manager has decided to create a new channel.</p>

        <p>If true on a requested channel, this indicates that the audio
          stream has already been requested and the client does not need to
          call RequestStreams, although it MAY still do so.</p>

        <p>If true on an unrequested (incoming) channel, this indicates that
          the remote contact initially requested an audio stream; this does
          not imply that that audio stream is still active (as indicated by
          <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel.Type.StreamedMedia">ListStreams</tp:dbus-ref>).</p>

        <p>This property is immutable (cannot change), and therefore SHOULD
          appear wherever immutable properties are reported, e.g. <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Connection.Interface.Requests">NewChannels</tp:dbus-ref>
          signals.</p>

        <tp:rationale><p>This reduces D-Bus round trips.</p></tp:rationale>

        <p>Connection managers capable of signalling audio calls to contacts
          SHOULD include a channel class in <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Connection.Interface.Requests">RequestableChannelClasses</tp:dbus-ref>
          with <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel">ChannelType</tp:dbus-ref>
          = <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel.Type">StreamedMedia</tp:dbus-ref>
          and <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel">TargetHandleType</tp:dbus-ref>
          = Contact in the fixed properties dictionary, and InitialAudio
          (and also InitialVideo, if applicable) in the allowed properties
          list. Clients wishing to discover whether a connection manager
          can signal audio and/or video calls SHOULD use this information.</p>

        <tp:rationale>
          <p>Not all protocols support signalling video calls, and it would be
            possible (although unlikely) to have a protocol where only video,
            and not audio, could be signalled.</p>
        </tp:rationale>

        <p>Connection managers that support the <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Connection.Interface">ContactCapabilities</tp:dbus-ref>
          interface SHOULD represent the capabilities of receiving audio
          and/or video calls by including a channel class in
          a contact's capabilities with ChannelType = StreamedMedia
          in the fixed properties dictionary, and InitialAudio and/or
          InitialVideo in the allowed properties list. Clients wishing to
          discover whether a particular contact is likely to be able to
          receive audio and/or video calls SHOULD use this information.</p>

        <tp:rationale>
          <p>Not all clients support video calls, and it would also be
            possible (although unlikely) to have a client which could only
            stream video, not audio.</p>
        </tp:rationale>

        <p>Clients that are willing to receive audio and/or video calls
          SHOULD include the following among their channel classes if
          calling <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Connection.Interface.ContactCapabilities">UpdateCapabilities</tp:dbus-ref>
          (clients of a <tp:dbus-ref
            namespace="org.freedesktop.Telepathy">ChannelDispatcher</tp:dbus-ref>
          SHOULD instead arrange for the ChannelDispatcher to do this,
          by including the filters in their <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Client.Handler">HandlerChannelFilter</tp:dbus-ref>
          properties):</p>

        <ul>
          <li>{ ChannelType = StreamedMedia }</li>
          <li>{ ChannelType = StreamedMedia, InitialAudio = true }
            if receiving calls with audio is supported</li>
          <li>{ ChannelType = StreamedMedia, InitialVideo = true }
            if receiving calls with video is supported</li>
        </ul>

        <tp:rationale>
          <p>Connection managers for protocols with capability discovery,
            like XMPP, need this information to advertise the appropriate
            capabilities for their protocol.</p>
        </tp:rationale>
      </tp:docstring>
    </property>

    <property name="InitialVideo" tp:name-for-bindings="Initial_Video"
      type="b" access="read">
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>The same as <tp:member-ref>InitialAudio</tp:member-ref>, but for
          a video stream. This property is immutable (cannot change).</p>

        <p>In particular, note that if this property is false, this does not
          imply that an active video stream has not been added, only that no
          video stream was active at the time the channel appeared.</p>

        <p>This property is the correct way to discover whether connection
          managers, contacts etc. support video calls; it appears in
          capabilities structures in the same way as InitialAudio.</p>
      </tp:docstring>
    </property>

    <property name="ImmutableStreams" tp:name-for-bindings="Immutable_Streams"
      type="b" access="read">
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>If <tt>True</tt>, once streams have been requested for this channel
          (either by setting <tp:member-ref>InitialAudio</tp:member-ref> or
          <tp:member-ref>InitialVideo</tp:member-ref> when the channel is
          requested, or by calling
          <tp:member-ref>RequestStreams</tp:member-ref> on a channel with no
          streams), a stream of a different content type cannot be added;
          subsequent calls to <tp:member-ref>RequestStreams</tp:member-ref>
          that attempt to do so will fail.</p>

        <p>If this property is missing, clients SHOULD assume that it is false,
          and thus that the channel's streams can be changed once the call has
          started.</p>

        <p>If this property is present in the "allowed" set in all of the
          StreamedMedia entries in a contact's capabilities, then user
          interfaces MAY choose to show a separate "call" option for each
          class of call.</p>

          <tp:rationale>
            <p>For example, once an audio-only Google Talk call has started,
              it is not possible to add a video stream; both audio and video
              must be requested at the start of the call if video is desired.
              User interfaces may use this pseudo-capability as a hint to
              display separate "Audio call" and "Video call" buttons, rather
              than a single "Call" button with the option to add and remove
              video once the call has started for contacts without this flag.
            </p>
          </tp:rationale>

        <p>This property is immutable, and therefore SHOULD be announced
          in <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Connection.Interface.Requests">NewChannels</tp:dbus-ref>,
          etc.</p>
      </tp:docstring>
    </property>

    <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
      <p>A channel that can send and receive streamed media such as audio or
        video.  Provides a number of methods for listing and requesting new
        streams, and signals to indicate when streams have been added, removed
        and changed status. The state of the call (ringing remotely, ringing
        locally, answered, missed, etc.) are represented using the properties
        and signals of the Group interface.</p>

      <p>In general this should be used in conjunction with the <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Interface">MediaSignalling</tp:dbus-ref>
        interface to exchange connection candidates and codec choices with
        whichever component is responsible for the streams. However, in certain
        applications where no candidate exchange is necessary (eg the streams
        are handled by specialised hardware which is controlled directly by the
        connection manager), the signalling interface can be omitted and this
        channel type used simply to control the streams.</p>

      <h4>Outgoing calls</h4>

      <p>To make an audio-only call to a contact <tt>foo@example.com</tt>,
        clients should call:</p>

      <blockquote>
        <pre>
<tp:dbus-ref
    namespace="org.freedesktop.Telepathy.Connection.Interface.Requests">CreateChannel</tp:dbus-ref>({
  <tp:dbus-ref
    namespace="org.freedesktop.Telepathy.Channel">ChannelType</tp:dbus-ref>: <tp:dbus-ref
    namespace="org.freedesktop.Telepathy.Channel.Type">StreamedMedia</tp:dbus-ref>,
  <tp:dbus-ref
    namespace="org.freedesktop.Telepathy.Channel">TargetHandleType</tp:dbus-ref>: Contact,
  <tp:dbus-ref
    namespace="org.freedesktop.Telepathy.Channel">TargetID</tp:dbus-ref>: 'foo@example.com',
  <tp:member-ref>InitialAudio</tp:member-ref>: True,
)</pre></blockquote>

      <p>As always, <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel">TargetHandle</tp:dbus-ref>
        may be used in place of TargetID if the contact's handle is already
        known. To make an audio-and-video call, the client should also specify
        <tp:member-ref>InitialVideo</tp:member-ref>.  The connection manager
        SHOULD return a channel whose immutable properties contain the local
        user as the <tp:dbus-ref namespace='ofdT.Channel'>InitiatorHandle</tp:dbus-ref>,
        the remote contact as the <tp:dbus-ref namespace='ofdT.Channel'>TargetHandle</tp:dbus-ref>,
        <tp:dbus-ref namespace='ofdT.Channel'>Requested</tp:dbus-ref> = <code>True</code>
        (indicating that the call is outgoing); the <tp:dbus-ref
          namespace='ofdT.Channel.Interface'>Group</tp:dbus-ref> interface should
        initially have the local user in <tp:dbus-ref
          namespace='ofdT.Channel.Interface.Group'>Members</tp:dbus-ref> and the remote
        contact in <tp:dbus-ref
          namespace='ofdT.Channel.Interface.Group'>RemotePendingMembers</tp:dbus-ref>, to
        indicate that we are awaiting their response.</p>

      <p>The contact answering the call is represented by the CM signalling
        <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Interface.Group">MembersChanged</tp:dbus-ref>,
        moving the remote contact to Members, with the remote contact as the
        <var>Actor</var> and <var>Reason</var> <code>None</code>. The contact
        rejecting the call is represented by both contacts being removed from
        the group, with the remote contact as the <var>Actor</var> and
        <var>Reason</var> set appropriately. The local user may hang up at any
        time by calling
        <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Interface.Group">RemoveMembersWithReason</tp:dbus-ref>
        to remove themself, with an appropriate reason; the CM SHOULD relay the
        reason to the remote contact, and emit MembersChanged removing both
        contacts from the group with the self handle as the <var>Actor</var>.</p>

      <p>(In the past, several other patterns have been used to place outgoing
        calls; see
        <a href="http://telepathy.freedesktop.org/wiki/Requesting%20StreamedMedia%20channels">'Requesting StreamedMedia Channels' on the Telepathy wiki</a>
        for the details.)</p>

      <h4>Incoming calls</h4>

      <p>Incoming calls' immutable properties should contain <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel">TargetHandleType</tp:dbus-ref>
        = Contact, both <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel">TargetHandle</tp:dbus-ref> and
        <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel">InitiatorHandle</tp:dbus-ref>
        set to the remote contact, <tp:dbus-ref
        namespace='ofdT.Channel'>Requested</tp:dbus-ref> = <code>False</code>
        (indicating that this is an incoming call), and appropriate values of
        <tp:member-ref>InitialAudio</tp:member-ref> and
        <tp:member-ref>InitialVideo</tp:member-ref>; the Group interface should
        initially have the local user in <tp:dbus-ref
        namespace="ofdT.Channel.Interface.Group">LocalPendingMembers</tp:dbus-ref>
        and the remote contact in <tp:dbus-ref
        namespace="ofdT.Channel.Interface.Group">Members</tp:dbus-ref>,
        indicating that the contact is awaiting our response.</p>

      <p>To accept the call, use <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Interface.Group">AddMembers</tp:dbus-ref>
        to move the local user to the group's members. To reject the call, use
        <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Interface.Group">RemoveMembersWithReason</tp:dbus-ref>
        to remove the local member from the group, with an appropriate reason.
        If the remote user ends the call before it is answered, this is
        represented by <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Interface.Group">MembersChanged</tp:dbus-ref>
        removing both parties from the group with the remote contact as the
        <var>Actor</var>, and <var>Reason</var> set appropriately.</p>

      <p>Note that the call may end with the self handle as the
        <var>Actor</var> without the user having chosen to reject the call, as
        indicated by the nature of the <var>Reason</var>. Specifically, some
        local component may time out the call (indicating this with reason
        <code>No_Answer</code>; for example, the CM may have forwarded the call
        to another number, as configured using <tp:dbus-ref
        namespace='ofdT.Connection.Interface'>Forwarding.DRAFT</tp:dbus-ref>),
        or something may have gone wrong with the call
        (indicated by reason <code>Error</code>). Such calls SHOULD be
        considered missed, just as if the remote contact had hung up before the
        local user answered the call.</p>

      <tp:rationale>
        <p>This is a bit awkward, but these are the best ways we can represent
          these situations. It's important to document which calls should be
          considered missed, to ensure that the user can be notified.</p>
      </tp:rationale>

      <p>When the local user accepts an incoming call, the connection manager
        SHOULD change the direction of any streams with pending local send
        to be sending, without altering whether those streams are
        receiving.</p>

      <tp:rationale>
        <p>This matches existing practice, and means that a client
          can answer incoming calls and get an unmuted microphone/activated
          webcam without having to take additional action to accept the
          stream directions.</p>

        <p>It does, however, introduce a race condition: a client believing
          that it is accepting an audio-only call by calling AddMembers
          can inadvertantly accept an audio + video call (and hence activate
          sending from a webcam without the user's permission) if a video
          stream is added just before AddMembers is processed. This race
          should be removed when this specification is revised.</p>
      </tp:rationale>

    <h4>During a call</h4>

    <p>If <tp:member-ref>ImmutableStreams</tp:member-ref> is
      <code>False</code>, new streams may be requested using
      <tp:member-ref>RequestStreams</tp:member-ref> (to add video to an
      audio-only call, for instance), and existing streams may be removed using
      <tp:member-ref>RemoveStreams</tp:member-ref> (for example, to downgrade
      an audio-video call to audio-only). The call may be ended by calling
      <tp:dbus-ref
        namespace="org.freedesktop.Telepathy.Channel.Interface.Group">RemoveMembers</tp:dbus-ref>
      or <tp:dbus-ref
        namespace="org.freedesktop.Telepathy.Channel.Interface.Group">RemoveMembersWithReason</tp:dbus-ref>; the call ending is signalled by the CM emitting <tp:dbus-ref
        namespace="org.freedesktop.Telepathy.Channel.Interface.Group">MembersChanged</tp:dbus-ref>,
      removing both parties from the group.</p>

    <h4>Handler filters</h4>

    <p>For historical reasons, handlers must specify more than one filter if
      they want to correctly advertise support for audio and/or video calls. If
      they can handle channels using the <tp:dbus-ref
        namespace="org.freedesktop.Telepathy.Channel.Interface">MediaSignalling</tp:dbus-ref>
      interface, they should also advertise various
      <tp:type>Handler_Capability_Token</tp:type>s to indicate which codecs and
      transports they support. See <tp:member-ref>InitialAudio</tp:member-ref>
      and <tp:dbus-ref
        namespace="org.freedesktop.Telepathy.Channel.Interface">MediaSignalling/video/h264</tp:dbus-ref>
      for the gory details. In summary:</p>

    <dl>
      <dt>To advertise support for streamed media in general, include the
        following filter in <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Client.Handler">HandlerChannelFilter</tp:dbus-ref>:</dt>
      <dd><pre>
{ '...Channel.ChannelType': '...Channel.Type.StreamedMedia' ,
  '...Channel.TargetHandleType': Contact,
}</pre></dd>

      <dt>To advertise support for audio calls, also include the following
        filter:</dt>
      <dd><pre>
{ '...Channel.ChannelType': '...Channel.Type.StreamedMedia' ,
  '...Channel.TargetHandleType': Contact,
  '...Channel.Type.StreamedMedia.InitialAudio': True,
}</pre></dd>

      <dt>To advertise support for video calls, also include the following
        filter:</dt>
      <dd><pre>
{ '...Channel.ChannelType': '...Channel.Type.StreamedMedia' ,
  '...Channel.TargetHandleType': Contact,
  '...Channel.Type.StreamedMedia.InitialVideo': True,
}</pre></dd>

      <dt>If you use telepathy-farsight, and have H.264 support, you probably
        want these <tp:dbus-ref
        namespace="org.freedesktop.Telepathy.Client.Handler">Capabilities</tp:dbus-ref>:</dt>
      <dd><pre>
[ "org.freedesktop.Telepathy.Channel.Interface.MediaSignalling/ice-udp",
  "org.freedesktop.Telepathy.Channel.Interface.MediaSignalling/gtalk-p2p",
  "org.freedesktop.Telepathy.Channel.Interface.MediaSignalling/video/h264",
]</pre></dd>
    </dl>
    </tp:docstring>

    <tp:flags name="Channel_Media_Capabilities" value-prefix="Channel_Media_Capability" type="u">
      <tp:docstring>
        The channel-type-specific capability flags used for
        Channel.Type.StreamedMedia in the <tp:dbus-ref
          namespace="org.freedesktop.Telepathy">Connection.Interface.Capabilities</tp:dbus-ref>
        interface. See the <tp:member-ref>InitialAudio</tp:member-ref>
        property for details of the mechanisms that will replace this.
      </tp:docstring>
      <tp:flag suffix="Audio" value="1">
        <tp:docstring>
          The handle is capable of using audio streams within a media channel.
        </tp:docstring>
      </tp:flag>
      <tp:flag suffix="Video" value="2">
        <tp:docstring>
          The handle is capable of using video streams within a media channel.
        </tp:docstring>
      </tp:flag>
      <tp:flag suffix="NAT_Traversal_STUN" value="4">
        <tp:docstring>
          The handle is capable of performing STUN to traverse NATs.
        </tp:docstring>
      </tp:flag>
      <tp:flag suffix="NAT_Traversal_GTalk_P2P" value="8">
        <tp:docstring>
          The handle is capable of establishing Google Talk peer-to-peer
          connections (as implemented in libjingle 0.3) to traverse NATs.
        </tp:docstring>
      </tp:flag>
      <tp:flag suffix="NAT_Traversal_ICE_UDP" value="16">
        <tp:docstring>
          The handle is capable of establishing ICE UDP peer-to-peer
          connections (as defined by the IETF MMUSIC working group) to traverse
          NATs.
        </tp:docstring>
      </tp:flag>

      <tp:flag suffix="Immutable_Streams" value="32">
        <tp:docstring>
          Channels whose target handle is this contact will have
          <tp:member-ref>ImmutableStreams</tp:member-ref> = <tt>True</tt>.
        </tp:docstring>
      </tp:flag>

    </tp:flags>

  </interface>
</node>
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