<s>
Fraunhofer	B-Operating_System
FDK	I-Operating_System
AAC	I-Operating_System
is	O
an	O
open-source	B-Application
library	B-Library
for	O
encoding	B-General_Concept
and	I-General_Concept
decoding	I-General_Concept
digital	O
audio	O
in	O
the	O
Advanced	B-Application
Audio	I-Application
Coding	I-Application
(	O
AAC	O
)	O
format	O
.	O
</s>
<s>
Fraunhofer	O
IIS	O
,	O
developed	O
this	O
library	B-Library
for	O
Android	B-Application
4.1	I-Application
.	O
</s>
<s>
It	O
supports	O
several	O
Audio	O
Object	O
Types	O
including	O
MPEG-2	B-Algorithm
and	O
MPEG-4	B-Application
AAC	I-Application
LC	O
,	O
HE-AAC	O
(	O
AAC	O
LC	O
+	O
SBR	B-Algorithm
)	O
,	O
HE-AACv2	O
(	O
LC	O
+	O
SBR	B-Algorithm
+	O
PS	O
)	O
as	O
well	O
AAC-LD	B-Algorithm
(	O
low	O
delay	O
)	O
and	O
AAC-ELD	B-Algorithm
(	O
enhanced	O
low	O
delay	O
)	O
for	O
real-time	O
communication	O
.	O
</s>
<s>
The	O
encoding	O
library	B-Library
supports	O
sample	O
rates	O
up	O
to	O
96kHz	O
and	O
up	O
to	O
eight	O
channels	O
(	O
7.1	O
surround	O
)	O
.	O
</s>
<s>
The	O
Android-targeted	O
implementation	O
of	O
the	O
Fraunhofer	O
AAC	O
encoder	O
uses	O
fixed-point	O
math	O
and	O
is	O
optimized	O
for	O
encoding	O
on	O
embedded	O
devices/mobile	O
phones	O
.	O
</s>
<s>
The	O
library	B-Library
is	O
currently	O
limited	O
to	O
16-bit	O
PCM	B-Algorithm
input	O
.	O
</s>
<s>
Other	O
versions	O
of	O
the	O
Fraunhofer	O
encoder	O
,	O
like	O
the	O
one	O
included	O
in	O
Winamp	B-Application
,	O
are	O
optimized	O
for	O
encoding	O
music	O
on	O
desktop-class	O
processors	O
.	O
</s>
<s>
Those	O
versions	O
of	O
the	O
encoder	O
,	O
however	O
,	O
are	O
not	O
open-source	B-Application
and	O
require	O
a	O
commercial	O
license	O
.	O
</s>
<s>
Version	O
2	O
of	O
the	O
library	B-Library
,	O
introduced	O
with	O
Android	B-Application
P	O
,	O
also	O
includes	O
support	O
for	O
xHE-AAC	O
and	O
AAC-ELD	B-Algorithm
v2	O
.	O
</s>
<s>
xHE-AAC	O
extends	O
the	O
operating	O
range	O
of	O
the	O
codec	B-General_Concept
from	O
12	O
to	O
300	O
kb/s	O
for	O
stereo	O
signals	O
and	O
allows	O
seamless	O
switching	O
between	O
bitrates	O
over	O
this	O
range	O
for	O
adaptive	O
bitrate	O
delivery	O
(	O
using	O
standards	O
such	O
as	O
MPEG-DASH	B-Protocol
or	O
HLS	B-Protocol
for	O
example	O
)	O
.	O
</s>
<s>
The	O
FDK	B-Operating_System
AAC	I-Operating_System
encoder	O
employs	O
a	O
more	O
aggressive	O
default	O
low-pass	B-Algorithm
filter	I-Algorithm
than	O
is	O
used	O
in	O
other	O
codecs	B-General_Concept
.	O
</s>
<s>
The	O
library	B-Library
allows	O
overriding	O
the	O
low-pass	B-Algorithm
filter	I-Algorithm
setting	O
,	O
and	O
in	O
the	O
highest	O
VBR	B-General_Concept
mode	O
effectively	O
applies	O
no	O
filter	O
at	O
all	O
.	O
</s>
<s>
The	O
code	O
compiles	O
into	O
a	O
shared	O
library	B-Library
,	O
libfdk-aac	O
.	O
</s>
<s>
The	O
media	O
frameworks	O
FFmpeg	B-Library
and	O
Libav	B-Language
support	O
audio	O
encoding	O
through	O
libfdk-aac	O
.	O
</s>
<s>
The	O
license	O
included	O
by	O
Fraunhofer	O
in	O
the	O
FDK	O
library	B-Library
source	O
code	O
allows	O
redistribution	O
in	O
source	O
or	O
binary	O
forms	O
,	O
but	O
does	O
not	O
license	O
patented	O
technologies	O
described	O
by	O
the	O
code	O
.	O
</s>
<s>
The	O
license	O
states	O
that	O
the	O
library	B-Library
may	O
only	O
be	O
used	O
for	O
purposes	O
as	O
authorized	O
by	O
patent	O
licenses	O
.	O
</s>
<s>
Due	O
to	O
this	O
restriction	O
,	O
along	O
with	O
a	O
limitation	O
on	O
charging	O
for	O
the	O
library	B-Library
,	O
Debian	O
considers	O
it	O
non-free	O
.	O
</s>
<s>
Via	O
Licensing	O
administers	O
a	O
patent	O
pool	O
that	O
includes	O
patent	O
licenses	O
for	O
the	O
AAC	O
codecs	B-General_Concept
,	O
including	O
xHE-AAC	O
and	O
MPEG-D	O
DRC	O
.	O
</s>
<s>
The	O
FDK	O
license	O
also	O
states	O
that	O
"	O
most	O
manufacturers	O
of	O
Android	B-Application
devices	O
already	O
license	O
these	O
patent	O
claims	O
through	O
Via	O
Licensing	O
or	O
directly	O
from	O
the	O
patent	O
owners	O
,	O
and	O
therefore	O
FDK	B-Operating_System
AAC	I-Operating_System
Codec	B-General_Concept
software	O
may	O
already	O
be	O
covered	O
under	O
those	O
patent	O
licenses	O
when	O
it	O
is	O
used	O
for	O
those	O
licensed	O
purposes	O
only.	O
"	O
</s>
