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LeAudio

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streams very difficult to implement private broadcasts bring a whole new dimension to
bluetooth le audio whether thats for personal tv and music access to a tv in a hotel
room shared audio in a conference room or the new bluetooth audio sharing experience it
section commanders
relies on a simple way for users to connect to the correct broadcast source and get access to
the broadcastcode to decrypt the audio all of this is managed by two new roles which are
defined in bap they are the scan delegator and the broadcast assistant they work with
the broadcast audio scanning service bass to distribute the information gathering and
control that provide the richness in broadcast applications
broadcast assistant s
broadcast assistant s allow other devices to perform the scanning job that we described in
section the broadcast assistant role is normally the main role of a stand alone
commander scanning on behalf of a broadcast sink there are two important reasons to
offload this task the first is that scanning is a fairly power hungry operation which is
something that you dont want a hearing aid or earbud to do or at least not very often
particularly without knowing exactly what its looking for its a job which is far better
performed on a d evice like a phone or a dedicated remote control neither of which are being
powered by tiny zinc air batteries the second reason is the user experience broadcasts
should always contain readable metadata in their base structures allowing a device wit h a
display to show what each is displaying that information is something which is easy to
implement on a phone or remote control but largely impossible on an earbud so moving
the scanning and selection task somewhere else not only saves battery life it vastly improves
the user experience
broadcast assistant s have an acl link with an acceptor if the acceptors a re running a cap
based profile th ey may be a member of coordinated set in which case each commander that
includes the broadcast assistant has to run the cap preamble procedure to ensure that it
operates on all of the set members multiple commanders can be involved so a user could
have a commander application in a smartwa tch as well as their smartphone and also a
dedicated remote control as an additional commander
scan delegators
commanders work on behalf of a device with a scan delegator role the role is defined in
bap and is normally implemented in a broadcast sink its job is to find ot her devices taking
the broadcast assistant role which can take over the job of scanning for broadcasters a
scan delegator can also be implemented in a commander as m ultiple commanders can be
chained together effectively relaying information from one to another well see the benefit
of that in a later chapter
the scan delegator role within a broadcast sink always contains an instance of bass scan
delegators solicit for broadcast assistant s which can scan on their behalf by sending
solicitation requests using extended advertising pdus which include a service data ad type
containing the bass uuid
chapter setting up and using broadcast audio streams
any broadcast assistant within range can connect and let the scan delegator know that it has
started scanning on its behalf interacting through the bass instance on the broadcast sink
where it writes to the broadcast audio scan control point characteristic bass to
confir m that it is actively scanning opcode x or has stopped scanning opcode x
it is up to the bass instance to record this status for multiple client s to determine whether
any are actively scanning this process of scanning on behalf of a scan delegator is called
remote broadcast scanning once it knows that a broadcast assistant is scanning on its
behalf a broadcast sink may decide to terminate its own scanning process to conserve power
the broadcast assistant can read the pac records of t he broadcast sink to discover its
capabilities and use that information to filter the broadcast source s it finds so that it only
presents the scan delegator with options which are valid for its broadcast sink most
commonly that would take into account the broadcast sink s audio location supported and
available context type s and the codec configurations it supports
once the broadcast assistant has detected a suitable broadcast source it can inform the scan
delegator by writing to one of its broadcast receive state characteristics to start the process
of the broadcast sink acquiring the broadcast audio stream this could be an automatic
action or it could be user initiated a user might want to automatically connect to a known
broadcast source such as when they walk into a place of worship or their office alternatively
they may ask their phone to scan and let them know whats available using a scanning
application before select ing their preferred broadcast source that choice is implementation
specific
adding a broadcast source to bass
once that choice has been made on a commander the broadcast assistant write s it to the
first empty broadcast receive state characteristic on the broadcast sink adding the selected
broadcast source information bap before it does this it should have read the current
status of the broadcast receive state characteristics if the user has chosen a broadcast source
which already exists in one of them then it should modify the appropriate broadcast source
value using the modify broadcast source procedure bap it should also check that the
broadcast sink is capable of decoding any propose d audio source
the parameters that it writes into the characteristic using the add source operation opcode
of x bass fall into three broad categories as shown in table
section commanders
parameter size
octets description
source information
advertiseraddresstype public x random x
advertiseraddress advertising address of the broadcast
source
advertisingsid id of the advertising set
broadcastid broadcast id of the broadcast source
action
pasync x dont synchronise
x synchronise using past
x synchronise without using past
painterval the syncinfo field interval
numsubgroups number of subgroups in the big
bissynci bisindex values to connect to
x dont synchronise to
bisindexik
x synchronise to bisindexik
configuration
metadata lengthi metadata length for the ith subgroup in
the big
metadata i varies metadata for the ith subgroup in the
big
table format of the add source operation
the first set of parameters the source information informs the broadcast sink of the