Datasets:
kkboy1
/
LeAudio

Dataset card Data Studio Files
xet
 Community
1
text
stringlengths
1
112
figure discovery of broadcast sink capabi lities and state by a broadcast assistant
once thats done and there is at least one active broadcast assistant scanning on behalf of the
scan delegator we move into baps broadcast assistant procedures starting with remote
broadcast scanning bap
remote broadcast scanning
a broadcast assistant that has informed the scan delegator that it is scanning will start
searching for broadcast transmitters as it finds each advertising set it will work its way
through the extended and periodic advertisement s auxadvind and
auxsyncind examining th e contents and parsing the structures to determine whether
the broadcast audio streams match the capabilities of the acceptor in most cases it will
build up a list of relevant available broadcast audio streams and present them to the user if
the comm ander has a suitable user interface such as an app on a smartphone this will
probably be presented in the form of a sorted list from which the user can select a broadcast
audio stream to connect to
section receiving broadcast audio streams with a commander
figure remote broadcast scanning
figure follows on from figure where broadcast assistant is scanning on behalf of
the two broadcast sink s shown here as a single entity it has discovered broadcast source
b and broadcast source c the user makes a decision on the commander to listen to
broadcast source c and selects i t at which point broadcast assistant writes the
information about broadcast source c to the bass instances in the scan delegators of the
two broadcast sink s
figure also shows how a collocated broadcast assistant can behave in this case broadcast
assistant is collocated with broadcast source a broadcast assistant has never written
to the broadcast scan control point to say it is scanning on behalf of the scan delegator as
its only purpose is to provide the scan delegator with information about its collocated
broadcast source as soon as it connect s to the scan delegator it can write that information
to a broadcast receive state a col located broadcast assistant can also perform scanning in
which case it would have told the scan delegator that it is scanning on its behalf but that is
an implementation choice
a practical point t o bear in mind is that t he receivers in broadcast assist ants may have better
sensitivity than the receivers in earbuds as they are likely to have larger antennas this means
that they will probably detect broadcast source s which would be out of range of their
broadcast sink s implementations may want to determine the rssi of signals fr om broadcast
source s and use that information to arrange the order of presentation of broadcast source s
to the user
chapter setting up and using broadcast audio streams
receiving a broadcast stream
we are now at the point where the user has decided what they want to listen to which takes
us back to the operation of adding a broadcast source which we described in section
in most cases when the user selects a broadcast source on their commander the broadcast
assistant will not just write the details of that source to the broadcast audio scan control
point characteristic but will also set the pasync a nd bissync parameters to instruct each
acceptor to start receiving the relevant streams
as the two acceptors are acting independently they may take different amounts of time to
obtain the pa train before they can synchronise with the appropriate bises particularly if they
have to scan rather than using past that could result in a noticeable delay between the time
that audio starts being rendered in the two earbuds the bluetooth specifications dont
contain any details on how to address this but o ne method is for the commander to do this
in two stages starting by setting the pasync bits waiting for notification that both acceptors
are synchronised and only at that point sending a modify source operation instructing them
to synchronise their bis es and receive and render audio
broadcastcodes revisited
in chapter we will see just how important broadcastcodes are for new audio applications
if we look back at figure and assume that the broadcast audio streams from both
broadcast source a and broadcast source c are encrypted theres likely to be a slightly
different way in which the two broadcastcodes would be obtained
broadcast source as broadcast assistant knows the broadcastcode for the streams thats
why its collocated so as soon as the user selects broadcast source a the broadcastcode
will be sent over in the add source command
in the case of broadcast source c the broadcast assistant may not know the code particularly
if it has not been paired with broadcast source c in this case one of the scan delegators
can ask all of its broadcast assistant s if they know the broadcastcode by notifying the
appropriate receive state characteristic with the bigencryption field set to x indicating
that it requires the broadcastcode if the broadcast sink already has a broadcastcode for
this stream wh ich no longer works normally because it was obtained in an earlier session it
should set the bigencryption field to x to indicate an incorrect broadcastcode and
include that value in the badcode field so that a broadcast a ssistant with the same bad code
doesnt waste time resending it any broadcast assistant can respond to this notification if
it knows the code by writing the broadcastcode value to the scan delegators broadcast
audio scan control point using the set b roadcast code operation x bass along
with the sourceid
section handovers between broadcast and unicast
as well see in chapter there is a range of out ofband methods by which a broadcast
assistant may obtain a broadcastcode opening up some interesting new use cases some of
these may directly trigger the broadcast audio stream acquisition process
ending reception of a broadcast audio stream
reception of a broadcast audio stream may be performed autonomously by an acceptor in
which case it will notify this change in its broad cast receive state characteristic if a
commander receives this notification and is aware that the acceptor is a member of a
coordinated set it may decide to terminate the reception on the other acceptors by writing
the appropriate value in their broad cast audio scan control points however this is
implementation specific
alternatively a user can use a commander to st op reception by writing to the broadcast audio
scan control points of each acceptor with the bissync value set to zero for all bises in all
subgroups and the pasync value set to x once the acceptor indicates that it is no longer
synchronised to either a bis or a pa by notifying its broadcast receive state characteristic
with both pasyncstate and bissyncstatei set to zero t he broadcast assistant should
perform the remove source operation x bass to remove the associated
broadcast receive state note that there is no state machine for the broadcast sink it uses
its broadcast rece ive state characteristic to synchronise or release broadcast audio streams
handovers between broadcast and unicast
two handover procedures are defined in cap to cover the use cases where an initiator wants
to move between a unicast and a broadcast stream or vice versa to transport the same audio
content this not the same as the general case of changing from a unicast use case to broadcast
use case but is specific to an application like sharing personal audio with friends where a user
wants to convert from a single personal stream to a broadcast one or vice versa the