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LeAudio

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khz rfu
table supported sampling frequencies x
the supportedframedurations ltv
the second codec capabilities ltv structure is the supportedframedurations type
x of table which provides information on the two frame durations supported by the
lc codec ms and ms when set to bits and indicate support for the two opti ons
of ms and ms frames for lc if both ms and ms are supported bits and can
section pacs the published audio capabilities service
be used to indicate whether one of them is preferred only one of bits and can be set
this ltv is also mandatory
bit all other bits
frame
duration rfu ms
preferred ms
preferred rfu rfu ms
supported ms
supported
table supported frame durations x
the supportedaudiochannelcounts ltv
the third ltv structure is the supportedaudiochannelcounts type x shown in
table this is another bitfield which indicates the number of audio channels which can
be included in a cis or bis channel count is the number of multiplexed audio channels
which can be carried in the same direction on a n isochronous stream which we covered in
section bits to indicate the number of channel counts that are supported with a value
of representing a supported option at least one bit must be set otherwise it indicates that
no audio channel can be set up if multiplexing is not supported then the channel count is
and this ltv structure can be omitted
bit
channel count rfu
table supported audio channel counts x
the supportedoctetspercodecframe ltv
the fourth ltv structure is the supportedoctetspercodecframe type x shown
in table this structure consists of two pairs of two octets with the lower pair octets
and specifying the minimum number of octets per codec frame and the upper pair the
maximum number of octets per codec frame both can be set to the same value where on ly a
specific number of octets is supported it defines the range of bitrates supported for the
selected sampling rate see table this ltv is also mandatory
octet
value rfu maximum number of octets per
codec frame minimum number of octets per
codec frame
table supported octets per codec frame x
the supportedmaxcodecframespersdu ltv
the fifth and final ltv structure in the supportedcodecspecificcapabilities is the
supportedmaxcodecframespersdu type x which is a single octet stating the
maximum number of codec frames which can be packed into a single sdu it can be omi tted
the bitrate is eight times the number of octets
chapter setting up unicast audio streams
if there is only one frame per sdu
the preferredaudiocontexts ltv
the codec specific capabilities can be followed by metadata which is formatted in an ltv
structure and described in the codec specific capabilities ltv structures section of the
generic audio assigned numbers document currently the only defined metadata that is
relevant for the pac record is the preferredaudiocontexts ltv this is a octet bitfield
of context type values using the standard val ues for context type s from the generic audio
assigned numbers document if a bit is set to b it signifies that this context type is a
preferred use case for the codec configuration in that pac record it would normally only be
present if the acceptor preferred specific pac records to be used for specific use cases
providing more granularity than the supportedaudiocontexts characteristic qv
minimum pacs capabilities for an audio sink
the mandatory bap lc requirements mean tha t an acceptor which is acting as a unicast
audio sink ie receiving an audio stream has to support reception of a minimum of one
audio channel at and khz sampling frequencies with a ms frame duration similarly
every acceptor which is acting a s a unicast audio source ie transmitting an audio stream
has to support encoding a minimum of one audio channel at a khz sampling frequency
with a ms frame duration
the mandatory khz sampling rate for both audio sink and source requires supp ort for
octets per sdu whilst the khz sampling rate for the audio sink requires octets for
the following example which illustrates pac records well just look at the sink pac
characteristic the same principles apply to the source pac charac teristic
the sink pac characteristic would normally expose these two mandatory codec settings in a
single pac record alternatively they could be separated into two pac records each
specifying a single set of capabilities bap only requires support fo r one audio channel audio
configuration in table of bap but to illustrate how pac records are built lets look at
an example of an acceptor which can support two audio channels corresponding to audio
configuration if it exposed these as fou r separate pac records they would look like table
section pacs the published audio capabilities service
pac record
codecid lc xd xd xd xd
supportedcodecspecificcapabilitieslength xb xb xb xb
supportedcodecspecificcapabilities
supportedsamplingfrequencies example khz x khz x
length x x x x
code x x x x
value x x x x
supportedframedurations example ms only
length x x x x
code x x x x
value x x x x
supported audio channel counts example x x
length x x x x
code x x x x
value x x x x
supported octets per codec frame example or x or xcc
length x x x x