<s>
Advanced	B-Application
Audio	I-Application
Coding	I-Application
(	O
AAC	O
)	O
is	O
an	O
audio	O
coding	O
standard	O
for	O
lossy	B-Algorithm
digital	O
audio	O
compression	O
.	O
</s>
<s>
Designed	O
to	O
be	O
the	O
successor	O
of	O
the	O
MP3	B-Application
format	O
,	O
AAC	O
generally	O
achieves	O
higher	O
sound	O
quality	O
than	O
MP3	B-Application
encoders	I-Application
at	O
the	O
same	O
bit	O
rate	O
.	O
</s>
<s>
AAC	O
has	O
been	O
standardized	O
by	O
ISO	O
and	O
IEC	O
as	O
part	O
of	O
the	O
MPEG-2	B-Algorithm
and	O
MPEG-4	B-Algorithm
specifications	O
.	O
</s>
<s>
Part	O
of	O
AAC	O
,	O
HE-AAC	O
(	O
"	O
AAC+	O
"	O
)	O
,	O
is	O
part	O
of	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
and	O
is	O
adopted	O
into	O
digital	O
radio	O
standards	O
DAB+	O
and	O
Digital	O
Radio	O
Mondiale	O
,	O
and	O
mobile	B-Application
television	I-Application
standards	O
DVB-H	B-Protocol
and	O
ATSC-M/H	B-Device
.	O
</s>
<s>
The	O
quality	O
for	O
stereo	O
is	O
satisfactory	O
to	O
modest	O
requirements	O
at	O
96kbit/s	O
in	O
joint	O
stereo	O
mode	O
;	O
however	O
,	O
hi-fi	B-Algorithm
transparency	I-Algorithm
demands	O
data	O
rates	O
of	O
at	O
least	O
128kbit/s	O
(	O
VBR	B-General_Concept
)	O
.	O
</s>
<s>
Tests	O
of	O
MPEG-4	B-Algorithm
audio	I-Algorithm
have	O
shown	O
that	O
AAC	O
meets	O
the	O
requirements	O
referred	O
to	O
as	O
"	O
transparent	O
"	O
for	O
the	O
ITU	O
at	O
128kbit/s	O
for	O
stereo	O
,	O
and	O
320kbit/s	O
for	O
5.1	O
audio	O
.	O
</s>
<s>
AAC	O
uses	O
only	O
a	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
algorithm	O
,	O
giving	O
it	O
higher	O
compression	O
efficiency	O
than	O
MP3	B-Application
,	O
which	O
uses	O
a	O
hybrid	O
coding	O
algorithm	O
that	O
is	O
part	O
MDCT	O
and	O
part	O
FFT	O
.	O
</s>
<s>
AAC	O
is	O
the	O
default	O
or	O
standard	O
audio	O
format	O
for	O
iPhone	B-Device
,	O
iPod	B-Device
,	O
iPad	B-Device
,	O
Nintendo	B-Device
DSi	I-Device
,	O
Nintendo	B-Operating_System
3DS	I-Operating_System
,	O
YouTube	B-Application
Music	I-Application
,	O
Apple	B-Operating_System
Music	I-Operating_System
,	O
iTunes	B-Operating_System
,	O
DivX	O
Plus	O
Web	O
Player	O
,	O
PlayStation	B-Operating_System
4	I-Operating_System
and	O
various	O
Nokia	B-Operating_System
Series	I-Operating_System
40	I-Operating_System
phones	O
.	O
</s>
<s>
It	O
is	O
supported	O
on	O
a	O
wide	O
range	O
of	O
devices	O
and	O
software	O
such	O
as	O
PlayStation	B-Device
Vita	I-Device
,	O
Wii	B-Operating_System
,	O
digital	O
audio	O
players	O
like	O
Sony	O
Walkman	O
or	O
SanDisk	O
Clip	O
,	O
Android	B-Application
and	O
BlackBerry	B-Application
devices	O
,	O
various	O
in-dash	O
car	O
audio	O
systems	O
,	O
and	O
is	O
also	O
one	O
of	O
the	O
audio	O
formats	O
used	O
on	O
the	O
Spotify	B-Application
web	O
player	O
.	O
</s>
<s>
The	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
,	O
a	O
type	O
of	O
transform	B-Algorithm
coding	I-Algorithm
for	O
lossy	B-Algorithm
compression	I-Algorithm
,	O
was	O
proposed	O
by	O
Nasir	O
Ahmed	O
in	O
1972	O
,	O
and	O
developed	O
by	O
Ahmed	O
with	O
T	O
.	O
Natarajan	O
and	O
K	O
.	O
R	O
.	O
Rao	O
in	O
1973	O
,	O
publishing	O
their	O
results	O
in	O
1974	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
development	O
of	O
the	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
,	O
proposed	O
by	O
J	O
.	O
P	O
.	O
Princen	O
,	O
A	O
.	O
W	O
.	O
Johnson	O
and	O
A	O
.	O
</s>
<s>
The	O
MP3	B-Application
audio	I-Application
coding	O
standard	O
introduced	O
in	O
1994	O
used	O
a	O
hybrid	O
coding	O
algorithm	O
that	O
is	O
part	O
MDCT	O
and	O
part	O
FFT	O
.	O
</s>
<s>
AAC	O
uses	O
a	O
purely	O
MDCT	O
algorithm	O
,	O
giving	O
it	O
higher	O
compression	O
efficiency	O
than	O
MP3	B-Application
.	O
</s>
<s>
It	O
is	O
specified	O
both	O
as	O
Part	O
7	O
of	O
the	O
MPEG-2	B-Algorithm
standard	O
,	O
and	O
Subpart	O
4	O
in	O
Part	O
3	O
of	O
the	O
MPEG-4	B-Algorithm
standard	O
.	O
</s>
<s>
In	O
1997	O
,	O
AAC	O
was	O
first	O
introduced	O
as	O
MPEG-2	B-Application
Part	I-Application
7	I-Application
,	O
formally	O
known	O
as	O
ISO/IEC	O
13818-7:1997	O
.	O
</s>
<s>
This	O
part	O
of	O
MPEG-2	B-Algorithm
was	O
a	O
new	O
part	O
,	O
since	O
MPEG-2	B-Algorithm
already	O
included	O
MPEG-2	B-Algorithm
Part	O
3	O
,	O
formally	O
known	O
as	O
ISO/IEC	B-Algorithm
13818-3	I-Algorithm
:	O
MPEG-2	B-Algorithm
BC	O
(	O
Backwards	B-General_Concept
Compatible	I-General_Concept
)	O
.	O
</s>
<s>
Therefore	O
,	O
MPEG-2	B-Application
Part	I-Application
7	I-Application
is	O
also	O
known	O
as	O
MPEG-2	B-Application
NBC	I-Application
(	O
Non-Backward	O
Compatible	O
)	O
,	O
because	O
it	O
is	O
not	O
compatible	O
with	O
the	O
MPEG-1	B-Algorithm
audio	O
formats	O
(	O
MP1	O
,	O
MP2	O
and	O
MP3	B-Application
)	O
.	O
</s>
<s>
MPEG-2	B-Application
Part	I-Application
7	I-Application
defined	O
three	O
profiles	O
:	O
Low-Complexity	O
profile	O
(	O
AAC-LC	B-Application
/	O
LC-AAC	B-Application
)	O
,	O
Main	O
profile	O
(	O
AAC	O
Main	O
)	O
and	O
Scalable	O
Sampling	O
Rate	O
profile	O
(	O
AAC-SSR	O
)	O
.	O
</s>
<s>
AAC-LC	B-Application
profile	O
consists	O
of	O
a	O
base	O
format	O
very	O
much	O
like	O
T	O
's	O
Perceptual	O
Audio	O
Coding	O
(	O
PAC	O
)	O
coding	O
format	O
,	O
with	O
the	O
addition	O
of	O
temporal	O
noise	O
shaping	O
(	O
TNS	O
)	O
,	O
the	O
Kaiser	O
window	O
(	O
described	O
below	O
)	O
,	O
a	O
nonuniform	O
quantizer	B-Algorithm
,	O
and	O
a	O
reworking	O
of	O
the	O
bitstream	O
format	O
to	O
handle	O
up	O
to	O
16	O
stereo	O
channels	O
,	O
16	O
mono	O
channels	O
,	O
16	O
low-frequency	O
effect	O
(	O
LFE	O
)	O
channels	O
and	O
16	O
commentary	O
channels	O
in	O
one	O
bitstream	O
.	O
</s>
<s>
In	O
1999	O
,	O
MPEG-2	B-Application
Part	I-Application
7	I-Application
was	O
updated	O
and	O
included	O
in	O
the	O
MPEG-4	B-Algorithm
family	O
of	O
standards	O
and	O
became	O
known	O
as	O
MPEG-4	B-Algorithm
Part	I-Algorithm
3	I-Algorithm
,	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
or	O
ISO/IEC	O
14496-3:1999	O
.	O
</s>
<s>
One	O
of	O
these	O
improvements	O
was	O
the	O
addition	O
of	O
Audio	O
Object	O
Types	O
which	O
are	O
used	O
to	O
allow	O
interoperability	O
with	O
a	O
diverse	O
range	O
of	O
other	O
audio	O
formats	O
such	O
as	O
TwinVQ	B-Algorithm
,	O
CELP	B-Algorithm
,	O
HVXC	B-Algorithm
,	O
Text-To-Speech	B-Application
Interface	O
and	O
MPEG-4	B-Application
Structured	I-Application
Audio	I-Application
.	O
</s>
<s>
In	O
that	O
regard	O
,	O
the	O
AAC	O
profiles	O
(	O
AAC-LC	B-Application
,	O
AAC	O
Main	O
and	O
AAC-SSR	O
profiles	O
)	O
are	O
combined	O
with	O
perceptual	O
noise	O
substitution	O
and	O
are	O
defined	O
in	O
the	O
MPEG-4	B-Algorithm
audio	I-Algorithm
standard	O
as	O
Audio	O
Object	O
Types	O
.	O
</s>
<s>
MPEG-4	B-Algorithm
Audio	I-Algorithm
Object	O
Types	O
are	O
combined	O
in	O
four	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
profiles	O
:	O
Main	O
(	O
which	O
includes	O
most	O
of	O
the	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
Object	O
Types	O
)	O
,	O
Scalable	O
(	O
AAC	O
LC	O
,	O
AAC	O
LTP	O
,	O
CELP	B-Algorithm
,	O
HVXC	B-Algorithm
,	O
TwinVQ	B-Algorithm
,	O
Wavetable	O
Synthesis	O
,	O
TTSI	O
)	O
,	O
Speech	O
(	O
CELP	B-Algorithm
,	O
HVXC	B-Algorithm
,	O
TTSI	O
)	O
and	O
Low	O
Rate	O
Synthesis	O
(	O
Wavetable	O
Synthesis	O
,	O
TTSI	O
)	O
.	O
</s>
<s>
The	O
reference	O
software	O
for	O
MPEG-4	B-Algorithm
Part	I-Algorithm
3	I-Algorithm
is	O
specified	O
in	O
MPEG-4	B-Algorithm
Part	I-Algorithm
5	I-Algorithm
and	O
the	O
conformance	O
bit-streams	O
are	O
specified	O
in	O
MPEG-4	B-Algorithm
Part	I-Algorithm
4	I-Algorithm
.	O
</s>
<s>
MPEG-4	B-Algorithm
Audio	I-Algorithm
remains	O
backward-compatible	B-General_Concept
with	O
MPEG-2	B-Application
Part	I-Application
7	I-Application
.	O
</s>
<s>
The	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
Version	O
2	O
(	O
ISO/IEC	O
14496-3:1999/Amd	O
1:2000	O
)	O
defined	O
new	O
audio	O
object	O
types	O
:	O
the	O
low	O
delay	O
AAC	O
(	O
AAC-LD	B-Algorithm
)	O
object	O
type	O
,	O
bit-sliced	O
arithmetic	O
coding	O
(	O
BSAC	O
)	O
object	O
type	O
,	O
parametric	O
audio	O
coding	O
using	O
harmonic	B-Algorithm
and	I-Algorithm
individual	I-Algorithm
line	I-Algorithm
plus	I-Algorithm
noise	I-Algorithm
and	O
error	O
resilient	O
(	O
ER	O
)	O
versions	O
of	O
object	O
types	O
.	O
</s>
<s>
The	O
HE-AAC	O
Profile	O
(	O
AAC	O
LC	O
with	O
SBR	B-Algorithm
)	O
and	O
AAC	O
Profile	O
(	O
AAC	O
LC	O
)	O
were	O
first	O
standardized	O
in	O
ISO/IEC	O
14496-3:2001/Amd	O
1:2003	O
.	O
</s>
<s>
The	O
HE-AAC	O
v2	O
Profile	O
(	O
AAC	O
LC	O
with	O
SBR	B-Algorithm
and	O
Parametric	O
Stereo	O
)	O
was	O
first	O
specified	O
in	O
ISO/IEC	O
14496-3:2005/Amd	O
2:2006	O
.	O
</s>
<s>
The	O
MPEG-4	B-Algorithm
Part	I-Algorithm
3	I-Algorithm
standard	O
also	O
contains	O
other	O
ways	O
of	O
compressing	O
sound	O
.	O
</s>
<s>
Advanced	B-Application
Audio	I-Application
Coding	I-Application
is	O
designed	O
to	O
be	O
the	O
successor	O
of	O
the	O
MPEG-1	B-Application
Audio	I-Application
Layer	I-Application
3	I-Application
,	O
known	O
as	O
MP3	B-Application
format	O
,	O
which	O
was	O
specified	O
by	O
ISO/IEC	O
in	O
11172-3	O
(	O
MPEG-1	B-Algorithm
Audio	O
)	O
and	O
13818-3	O
(	O
MPEG-2	B-Algorithm
Audio	O
)	O
.	O
</s>
<s>
Blind	O
tests	O
in	O
the	O
late	O
1990s	O
showed	O
that	O
AAC	O
demonstrated	O
greater	O
sound	O
quality	O
and	O
transparency	B-Algorithm
than	O
MP3	B-Application
for	O
files	O
coded	O
at	O
the	O
same	O
bit	O
rate	O
.	O
</s>
<s>
more	O
sample	O
rates	O
(	O
from	O
8	O
to	O
96	O
kHz	O
)	O
than	O
MP3	B-Application
(	O
16	O
to	O
48kHz	O
)	O
;	O
</s>
<s>
up	O
to	O
48	O
channels	O
(	O
MP3	B-Application
supports	O
up	O
to	O
two	O
channels	O
in	O
MPEG-1	B-Algorithm
mode	O
and	O
up	O
to	O
5.1	O
channels	O
in	O
MPEG-2	B-Algorithm
mode	O
)	O
;	O
</s>
<s>
AAC	O
uses	O
a	O
pure	O
MDCT	O
(	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
)	O
,	O
rather	O
than	O
MP3	B-Application
's	O
hybrid	O
coding	O
(	O
which	O
was	O
part	O
MDCT	O
and	O
part	O
FFT	O
)	O
;	O
</s>
<s>
higher	O
coding	O
efficiency	O
for	O
stationary	B-Algorithm
signals	I-Algorithm
(	O
AAC	O
uses	O
a	O
blocksize	O
of	O
1024	O
or	O
960	O
samples	O
,	O
allowing	O
more	O
efficient	O
coding	O
than	O
MP3	B-Application
's	O
576	O
sample	O
blocks	O
)	O
;	O
</s>
<s>
higher	O
coding	O
accuracy	O
for	O
transient	O
signals	O
(	O
AAC	O
uses	O
a	O
blocksize	O
of	O
128	O
or	O
120	O
samples	O
,	O
allowing	O
more	O
accurate	O
coding	O
than	O
MP3	B-Application
's	O
192	O
sample	O
blocks	O
)	O
;	O
</s>
<s>
Overall	O
,	O
the	O
AAC	B-Application
format	I-Application
allows	O
developers	O
more	O
flexibility	O
to	O
design	O
codecs	B-General_Concept
than	O
MP3	B-Application
does	O
,	O
and	O
corrects	O
many	O
of	O
the	O
design	O
choices	O
made	O
in	O
the	O
original	O
MPEG-1	B-Algorithm
audio	O
specification	O
.	O
</s>
<s>
This	O
is	O
especially	O
true	O
at	O
very	O
low	O
bit	O
rates	O
where	O
the	O
superior	O
stereo	O
coding	O
,	O
pure	O
MDCT	O
,	O
and	O
better	O
transform	O
window	O
sizes	O
leave	O
MP3	B-Application
unable	O
to	O
compete	O
.	O
</s>
<s>
While	O
the	O
MP3	B-Application
format	O
has	O
near-universal	O
hardware	O
and	O
software	O
support	O
,	O
primarily	O
because	O
MP3	B-Application
was	O
the	O
format	O
of	O
choice	O
during	O
the	O
crucial	O
first	O
few	O
years	O
of	O
widespread	O
music	O
file-sharing/distribution	O
over	O
the	O
internet	O
,	O
AAC	O
is	O
a	O
strong	O
contender	O
due	O
to	O
some	O
unwavering	O
industry	O
support	O
.	O
</s>
<s>
AAC	O
is	O
a	O
wideband	B-Algorithm
audio	I-Algorithm
coding	O
algorithm	O
that	O
exploits	O
two	O
primary	O
coding	O
strategies	O
to	O
dramatically	O
reduce	O
the	O
amount	O
of	O
data	O
needed	O
to	O
represent	O
high-quality	O
digital	O
audio	O
:	O
</s>
<s>
The	O
signal	O
is	O
converted	O
from	O
time-domain	O
to	O
frequency-domain	O
using	O
forward	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
.	O
</s>
<s>
In	O
order	O
to	O
prevent	O
corrupt	O
samples	O
,	O
a	O
modern	O
implementation	O
of	O
the	O
Luhn	B-Algorithm
mod	I-Algorithm
N	I-Algorithm
algorithm	I-Algorithm
is	O
applied	O
to	O
each	O
frame	O
.	O
</s>
<s>
The	O
MPEG-4	B-Algorithm
audio	I-Algorithm
standard	O
does	O
not	O
define	O
a	O
single	O
or	O
small	O
set	O
of	O
highly	O
efficient	O
compression	O
schemes	O
but	O
rather	O
a	O
complex	O
toolbox	O
to	O
perform	O
a	O
wide	O
range	O
of	O
operations	O
from	O
low	O
bit	O
rate	O
speech	O
coding	O
to	O
high-quality	O
audio	O
coding	O
and	O
music	O
synthesis	O
.	O
</s>
<s>
The	O
MPEG-4	B-Algorithm
audio	I-Algorithm
coding	O
algorithm	O
family	O
spans	O
the	O
range	O
from	O
low	O
bit	O
rate	O
speech	O
encoding	O
(	O
down	O
to	O
2kbit/s	O
)	O
to	O
high-quality	O
audio	O
coding	O
(	O
at	O
64kbit/s	O
per	O
channel	O
and	O
higher	O
)	O
.	O
</s>
<s>
In	O
contrast	O
to	O
MP3	B-Application
's	O
hybrid	O
filter	O
bank	O
,	O
AAC	O
uses	O
the	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
together	O
with	O
the	O
increased	O
window	O
lengths	O
of	O
1024	O
or	O
960	O
points	O
.	O
</s>
<s>
If	O
a	O
signal	O
change	O
or	O
a	O
transient	O
occurs	O
,	O
8	O
shorter	O
windows	B-Application
of	O
128/120	O
points	O
each	O
are	O
chosen	O
for	O
their	O
better	O
temporal	O
resolution	O
.	O
</s>
<s>
The	O
MPEG-2	B-Application
Part	I-Application
7	I-Application
standard	O
(	O
Advanced	B-Application
Audio	I-Application
Coding	I-Application
)	O
was	O
first	O
published	O
in	O
1997	O
and	O
offers	O
three	O
default	O
profiles	O
:	O
</s>
<s>
The	O
MPEG-4	B-Algorithm
Part	I-Algorithm
3	I-Algorithm
standard	O
(	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
)	O
defined	O
various	O
new	O
compression	O
tools	O
(	O
a.k.a.	O
</s>
<s>
AAC	O
is	O
not	O
used	O
in	O
some	O
of	O
the	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
profiles	O
.	O
</s>
<s>
The	O
MPEG-2	B-Application
Part	I-Application
7	I-Application
AAC	O
LC	O
profile	O
,	O
AAC	O
Main	O
profile	O
and	O
AAC	O
SSR	O
profile	O
are	O
combined	O
with	O
Perceptual	O
Noise	O
Substitution	O
and	O
defined	O
in	O
the	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
standard	O
as	O
Audio	O
Object	O
Types	O
(	O
under	O
the	O
name	O
AAC	O
LC	O
,	O
AAC	O
Main	O
and	O
AAC	O
SSR	O
)	O
.	O
</s>
<s>
These	O
are	O
combined	O
with	O
other	O
Object	O
Types	O
in	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
profiles	O
.	O
</s>
<s>
Here	O
is	O
a	O
list	O
of	O
some	O
audio	O
profiles	O
defined	O
in	O
the	O
MPEG-4	B-Algorithm
standard	O
:	O
</s>
<s>
One	O
of	O
many	O
improvements	O
in	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
is	O
an	O
Object	O
Type	O
called	O
Long	O
Term	O
Prediction	O
(	O
LTP	O
)	O
,	O
which	O
is	O
an	O
improvement	O
of	O
the	O
Main	O
profile	O
using	O
a	O
forward	O
predictor	O
with	O
lower	O
computational	O
complexity	O
.	O
</s>
<s>
Independent	O
error	O
correcting	O
codes	O
can	O
be	O
applied	O
to	O
any	O
of	O
these	O
parts	O
using	O
the	O
Error	O
Protection	O
(	O
EP	O
)	O
tool	O
defined	O
in	O
MPEG-4	B-Algorithm
Audio	I-Algorithm
standard	O
.	O
</s>
<s>
The	O
audio	O
coding	O
standards	O
MPEG-4	B-Algorithm
Low	O
Delay	O
(	O
AAC-LD	B-Algorithm
)	O
,	O
Enhanced	O
Low	O
Delay	O
(	O
AAC-ELD	O
)	O
,	O
and	O
Enhanced	O
Low	O
Delay	O
v2	O
(	O
AAC-ELDv2	O
)	O
as	O
defined	O
in	O
ISO/IEC	O
14496-3:2009	O
and	O
ISO/IEC	O
14496-3:2009/Amd	O
3	O
are	O
designed	O
to	O
combine	O
the	O
advantages	O
of	O
perceptual	O
audio	O
coding	O
with	O
the	O
low	O
delay	O
necessary	O
for	O
two-way	O
communication	O
.	O
</s>
<s>
They	O
are	O
closely	O
derived	O
from	O
the	O
MPEG-2	B-Algorithm
Advanced	B-Application
Audio	I-Application
Coding	I-Application
(	O
AAC	O
)	O
format	O
.	O
</s>
<s>
AAC-ELD	O
is	O
recommended	O
by	O
GSMA	O
as	O
super-wideband	O
voice	O
codec	B-General_Concept
in	O
the	O
IMS	O
Profile	O
for	O
High	O
Definition	O
Video	O
Conference	O
(	O
HDVC	O
)	O
Service	O
.	O
</s>
<s>
No	O
licenses	O
or	O
payments	O
are	O
required	O
for	O
a	O
user	O
to	O
stream	O
or	O
distribute	O
content	O
in	O
AAC	B-Application
format	I-Application
.	O
</s>
<s>
This	O
reason	O
alone	O
might	O
have	O
made	O
AAC	O
a	O
more	O
attractive	O
format	O
to	O
distribute	O
content	O
than	O
its	O
predecessor	O
MP3	B-Application
,	O
particularly	O
for	O
streaming	O
content	O
(	O
such	O
as	O
Internet	O
radio	O
)	O
depending	O
on	O
the	O
use	O
case	O
.	O
</s>
<s>
However	O
,	O
a	O
patent	O
license	O
is	O
required	O
for	O
all	O
manufacturers	O
or	O
developers	O
of	O
AAC	O
"	O
end-user	O
"	O
codecs	B-General_Concept
.	O
</s>
<s>
It	O
used	O
to	O
be	O
common	O
for	O
free	B-Application
and	I-Application
open	I-Application
source	I-Application
software	I-Application
implementations	O
such	O
as	O
FFmpeg	B-Library
and	O
FAAC	B-Operating_System
to	O
only	O
distribute	O
in	O
source	O
code	O
form	O
so	O
as	O
to	O
not	O
"	O
otherwise	O
supply	O
"	O
an	O
AAC	O
codec	B-General_Concept
.	O
</s>
<s>
However	O
,	O
FFmpeg	B-Library
has	O
since	O
become	O
more	O
lenient	O
on	O
patent	O
matters	O
:	O
the	O
"	O
gyan.dev	O
"	O
builds	O
recommended	O
by	O
the	O
official	O
site	O
now	O
contains	O
its	O
AAC	O
codec	B-General_Concept
,	O
with	O
the	O
FFmpeg	B-Library
legal	O
page	O
stating	O
that	O
patent	O
law	O
conformance	O
is	O
the	O
user	O
's	O
responsibility	O
.	O
</s>
<s>
Some	O
extensions	O
have	O
been	O
added	O
to	O
the	O
first	O
AAC	O
standard	O
(	O
defined	O
in	O
MPEG-2	B-Application
Part	I-Application
7	I-Application
in	O
1997	O
)	O
:	O
</s>
<s>
Perceptual	O
Noise	O
Substitution	O
(	O
PNS	O
)	O
,	O
added	O
in	O
MPEG-4	B-Algorithm
in	O
1999	O
.	O
</s>
<s>
It	O
allows	O
the	O
coding	O
of	O
noise	O
as	O
pseudorandom	B-Error_Name
data	I-Error_Name
.	O
</s>
<s>
Long	O
Term	O
Predictor	O
(	O
LTP	O
)	O
,	O
added	O
in	O
MPEG-4	B-Algorithm
in	O
1999	O
.	O
</s>
<s>
aacPlus	O
v1	O
or	O
AAC+	O
,	O
the	O
combination	O
of	O
SBR	B-Algorithm
(	O
Spectral	B-Algorithm
Band	I-Algorithm
Replication	I-Algorithm
)	O
and	O
AAC	O
LC	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
MP4	O
,	O
3GP	O
and	O
other	O
container	O
formats	O
based	O
on	O
ISO	O
base	O
media	O
file	O
format	O
for	O
file	O
storage	O
,	O
AAC	O
audio	O
data	O
was	O
first	O
packaged	O
in	O
a	O
file	O
for	O
the	O
MPEG-2	B-Algorithm
standard	O
using	O
Audio	O
Data	O
Interchange	O
Format	O
(	O
ADIF	O
)	O
,	O
consisting	O
of	O
a	O
single	O
header	O
followed	O
by	O
the	O
raw	O
AAC	O
audio	O
data	O
blocks	O
.	O
</s>
<s>
However	O
,	O
if	O
the	O
data	O
is	O
to	O
be	O
streamed	O
within	O
an	O
MPEG-2	B-Algorithm
transport	O
stream	O
,	O
a	O
self-synchronizing	O
format	O
called	O
an	O
Audio	O
Data	O
Transport	O
Stream	O
(	O
ADTS	O
)	O
is	O
used	O
,	O
consisting	O
of	O
a	O
series	O
of	O
frames	O
,	O
each	O
frame	O
having	O
a	O
header	O
followed	O
by	O
the	O
AAC	O
audio	O
data	O
.	O
</s>
<s>
This	O
file	O
and	O
streaming-based	O
format	O
are	O
defined	O
in	O
MPEG-2	B-Application
Part	I-Application
7	I-Application
,	O
but	O
are	O
only	O
considered	O
informative	O
by	O
MPEG-4	B-Algorithm
,	O
so	O
an	O
MPEG-4	B-Algorithm
decoder	O
does	O
not	O
need	O
to	O
support	O
either	O
format	O
.	O
</s>
<s>
These	O
containers	O
,	O
as	O
well	O
as	O
a	O
raw	O
AAC	O
stream	O
,	O
may	O
bear	O
the	O
.aac	B-Application
file	O
extension	O
.	O
</s>
<s>
MPEG-4	B-Algorithm
Part	I-Algorithm
3	I-Algorithm
also	O
defines	O
its	O
own	O
self-synchronizing	O
format	O
called	O
a	O
Low	O
Overhead	O
Audio	O
Stream	O
(	O
LOAS	O
)	O
that	O
encapsulates	O
not	O
only	O
AAC	O
,	O
but	O
any	O
MPEG-4	B-Algorithm
audio	I-Algorithm
compression	O
scheme	O
such	O
as	O
TwinVQ	B-Algorithm
and	O
ALS	B-Algorithm
.	O
</s>
<s>
This	O
format	O
is	O
what	O
was	O
defined	O
for	O
use	O
in	O
DVB	B-Application
transport	O
streams	O
when	O
encoders	O
use	O
either	O
SBR	B-Algorithm
or	O
parametric	O
stereo	O
AAC	O
extensions	O
.	O
</s>
<s>
In	O
December	O
2003	O
,	O
Japan	O
started	O
broadcasting	O
terrestrial	O
DTV	O
ISDB-T	O
standard	O
that	O
implements	O
MPEG-2	B-Algorithm
video	O
and	O
MPEG-2	B-Application
AAC	I-Application
audio	O
.	O
</s>
<s>
In	O
April	O
2006	O
Japan	O
started	O
broadcasting	O
the	O
ISDB-T	O
mobile	O
sub-program	O
,	O
called	O
1seg	O
,	O
that	O
was	O
the	O
first	O
implementation	O
of	O
video	O
H.264/AVC	B-Application
with	O
audio	O
HE-AAC	O
in	O
Terrestrial	O
HDTV	O
broadcasting	O
service	O
on	O
the	O
planet	O
.	O
</s>
<s>
In	O
December	O
2007	O
,	O
Brazil	O
started	O
broadcasting	O
terrestrial	O
DTV	O
standard	O
called	O
International	O
ISDB-Tb	B-Application
that	O
implements	O
video	O
coding	O
H.264/AVC	B-Application
with	O
audio	O
AAC-LC	B-Application
on	O
main	O
program	O
(	O
single	O
or	O
multi	O
)	O
and	O
video	O
H.264/AVC	B-Application
with	O
audio	O
HE-AACv2	O
in	O
the	O
1seg	O
mobile	O
sub-program	O
.	O
</s>
<s>
The	O
ETSI	O
,	O
the	O
standards	O
governing	O
body	O
for	O
the	O
DVB	B-Application
suite	I-Application
,	O
supports	O
AAC	O
,	O
HE-AAC	O
and	O
HE-AAC	O
v2	O
audio	O
coding	O
in	O
DVB	B-Application
applications	O
since	O
at	O
least	O
2004	O
.	O
</s>
<s>
DVB	B-Application
broadcasts	O
which	O
use	O
the	O
H.264	B-Application
compression	O
for	O
video	O
normally	O
use	O
HE-AAC	O
for	O
audio	O
.	O
</s>
<s>
In	O
April	O
2003	O
,	O
Apple	O
brought	O
mainstream	O
attention	O
to	O
AAC	O
by	O
announcing	O
that	O
its	O
iTunes	B-Operating_System
and	O
iPod	B-Device
products	O
would	O
support	O
songs	O
in	O
MPEG-4	B-Application
AAC	I-Application
format	O
(	O
via	O
a	O
firmware	B-Application
update	O
for	O
older	O
iPods	B-Device
)	O
.	O
</s>
<s>
Customers	O
could	O
download	O
music	O
in	O
a	O
closed-source	O
Digital	O
Rights	O
Management	O
(	O
DRM	O
)	O
-restricted	O
form	O
of	O
128	O
kbit/s	O
AAC	O
(	O
see	O
FairPlay	B-Operating_System
)	O
via	O
the	O
iTunes	B-Operating_System
Store	O
or	O
create	O
files	O
without	O
DRM	O
from	O
their	O
own	O
CDs	O
using	O
iTunes	B-Operating_System
.	O
</s>
<s>
On	O
May	O
29	O
,	O
2007	O
,	O
Apple	O
began	O
selling	O
songs	O
and	O
music	O
videos	O
from	O
participating	O
record	O
labels	O
at	O
higher	O
bitrate	O
(	O
256	O
kbit/s	O
cVBR	O
)	O
and	O
free	O
of	O
DRM	O
,	O
a	O
format	O
dubbed	O
"	O
iTunes	B-Operating_System
Plus	O
"	O
.	O
</s>
<s>
These	O
files	O
mostly	O
adhere	O
to	O
the	O
AAC	O
standard	O
and	O
are	O
playable	O
on	O
many	O
non-Apple	O
products	O
but	O
they	O
do	O
include	O
custom	O
iTunes	B-Operating_System
information	O
such	O
as	O
album	O
artwork	O
and	O
a	O
purchase	O
receipt	O
,	O
so	O
as	O
to	O
identify	O
the	O
customer	O
in	O
case	O
the	O
file	O
is	O
leaked	O
out	O
onto	O
peer-to-peer	O
networks	O
.	O
</s>
<s>
As	O
of	O
January	O
6	O
,	O
2009	O
,	O
nearly	O
all	O
music	O
on	O
the	O
USA	O
regioned	O
iTunes	B-Operating_System
Store	O
became	O
DRM-free	O
,	O
with	O
the	O
remainder	O
becoming	O
DRM-free	O
by	O
the	O
end	O
of	O
March	O
2009	O
.	O
</s>
<s>
iTunes	B-Operating_System
offers	O
a	O
"	O
Variable	B-General_Concept
Bit	I-General_Concept
Rate	I-General_Concept
"	O
encoding	O
option	O
which	O
encodes	O
AAC	O
tracks	O
in	O
the	O
Constrained	B-General_Concept
Variable	I-General_Concept
Bitrate	I-General_Concept
scheme	O
(	O
a	O
less	O
strict	O
variant	O
of	O
ABR	O
encoding	O
)	O
;	O
the	O
underlying	O
QuickTime	B-Application
API	O
does	O
offer	O
a	O
true	O
VBR	B-General_Concept
encoding	O
profile	O
however	O
.	O
</s>
<s>
As	O
of	O
September	O
2009	O
,	O
Apple	O
has	O
added	O
support	O
for	O
HE-AAC	O
(	O
which	O
is	O
fully	O
part	O
of	O
the	O
MP4	O
standard	O
)	O
only	O
for	O
radio	O
streams	O
,	O
not	O
file	O
playback	O
,	O
and	O
iTunes	B-Operating_System
still	O
lacks	O
support	O
for	O
true	O
VBR	B-General_Concept
encoding	O
.	O
</s>
<s>
For	O
a	O
number	O
of	O
years	O
,	O
many	O
mobile	O
phones	O
from	O
manufacturers	O
such	O
as	O
Nokia	O
,	O
Motorola	O
,	O
Samsung	B-Application
,	O
Sony	O
Ericsson	O
,	O
BenQ-Siemens	O
and	O
Philips	O
have	O
supported	O
AAC	O
playback	O
.	O
</s>
<s>
The	O
first	O
such	O
phone	O
was	O
the	O
Nokia	O
5510	O
released	O
in	O
2002	O
which	O
also	O
plays	O
MP3s	B-Application
.	O
</s>
<s>
However	O
,	O
this	O
phone	O
was	O
a	O
commercial	O
failure	O
and	O
such	O
phones	O
with	O
integrated	O
music	O
players	O
did	O
not	O
gain	O
mainstream	O
popularity	O
until	O
2005	O
when	O
the	O
trend	O
of	O
having	O
AAC	O
as	O
well	O
as	O
MP3	B-Application
support	O
continued	O
.	O
</s>
<s>
Sony	O
Ericsson	O
phones	O
support	O
various	O
AAC	B-Application
formats	I-Application
in	O
MP4	O
container	O
.	O
</s>
<s>
AAC-LC	B-Application
is	O
supported	O
in	O
all	O
phones	O
beginning	O
with	O
K700	O
,	O
phones	O
beginning	O
with	O
W550	O
have	O
support	O
of	O
HE-AAC	O
.	O
</s>
<s>
The	O
latest	O
devices	O
such	O
as	O
the	O
P990	B-Operating_System
,	O
K610	B-Device
,	O
W890i	B-Device
and	O
later	O
support	O
HE-AAC	O
v2	O
.	O
</s>
<s>
Nokia	O
XpressMusic	O
and	O
other	O
new	O
generation	O
Nokia	O
multimedia	O
phones	O
like	O
N	O
-	O
and	O
E-Series	O
also	O
support	O
AAC	B-Application
format	I-Application
in	O
LC	O
,	O
HE	O
,	O
M4A	O
and	O
HEv2	O
profiles	O
.	O
</s>
<s>
BlackBerry	B-Operating_System
phones	I-Operating_System
running	O
the	O
BlackBerry	B-Application
10	I-Application
operating	O
system	O
support	O
AAC	O
playback	O
natively	O
.	O
</s>
<s>
Select	O
previous	O
generation	O
BlackBerry	B-Application
OS	I-Application
devices	O
also	O
support	O
AAC	O
.	O
</s>
<s>
Apple	O
's	O
iPhone	B-Device
supports	O
AAC	O
and	O
FairPlay	B-Operating_System
protected	B-Application
AAC	I-Application
files	O
formerly	O
used	O
as	O
the	O
default	O
encoding	O
format	O
in	O
the	O
iTunes	B-Operating_System
Store	O
until	O
the	O
removal	O
of	O
DRM	O
restrictions	O
in	O
March	O
2009	O
.	O
</s>
<s>
Android	B-Application
2.3	O
and	O
later	O
supports	O
AAC-LC	B-Application
,	O
HE-AAC	O
and	O
HE-AAC	O
v2	O
in	O
MP4	O
or	O
M4A	O
containers	O
along	O
with	O
several	O
other	O
audio	O
formats	O
.	O
</s>
<s>
Android	B-Application
3.1	O
and	O
later	O
supports	O
raw	O
ADTS	O
files	O
.	O
</s>
<s>
Android	B-Application
4.1	O
can	O
encode	O
AAC	O
.	O
</s>
<s>
WebOS	B-Operating_System
by	O
HP/Palm	O
supports	O
AAC	O
,	O
AAC+	O
,	O
eAAC+	O
,	O
and	O
.m4a	O
containers	O
in	O
its	O
native	O
music	O
player	O
as	O
well	O
as	O
several	O
third-party	O
players	O
.	O
</s>
<s>
However	O
,	O
it	O
does	O
not	O
support	O
Apple	O
's	O
FairPlay	B-Operating_System
DRM	I-Operating_System
files	O
downloaded	O
from	O
iTunes	B-Operating_System
.	O
</s>
<s>
Windows	B-Protocol
Phone	I-Protocol
's	O
Silverlight	B-Application
runtime	O
supports	O
AAC-LC	B-Application
,	O
HE-AAC	O
and	O
HE-AAC	O
v2	O
decoding	O
.	O
</s>
<s>
Palm	B-Operating_System
OS	I-Operating_System
PDAs	B-Application
:	O
Many	O
Palm	B-Operating_System
OS	I-Operating_System
based	O
PDAs	B-Application
and	O
smartphones	O
can	O
play	O
AAC	O
and	O
HE-AAC	O
with	O
the	O
3rd	O
party	O
software	O
Pocket	O
Tunes	O
.	O
</s>
<s>
The	O
AAC	O
codec	B-General_Concept
for	O
TCPMP	B-Language
,	O
a	O
popular	O
video	O
player	O
,	O
was	O
withdrawn	O
after	O
version	O
0.66	O
due	O
to	O
patent	O
issues	O
,	O
but	O
can	O
still	O
be	O
downloaded	O
from	O
sites	O
other	O
than	O
corecodec.org	O
.	O
</s>
<s>
CorePlayer	B-Language
,	O
the	O
commercial	O
follow-on	O
to	O
TCPMP	B-Language
,	O
includes	O
AAC	O
support	O
.	O
</s>
<s>
Other	O
Palm	B-Operating_System
OS	I-Operating_System
programs	O
supporting	O
AAC	O
include	O
Kinoma	O
Player	O
and	O
AeroPlayer	O
.	O
</s>
<s>
Sony	B-Application
Reader	I-Application
:	O
plays	O
M4A	O
files	O
containing	O
AAC	O
,	O
and	O
displays	O
metadata	O
created	O
by	O
iTunes	B-Operating_System
.	O
</s>
<s>
Other	O
Sony	O
products	O
,	O
including	O
the	O
A	O
and	O
E	O
series	O
Network	O
Walkmans	O
,	O
support	O
AAC	O
with	O
firmware	B-Application
updates	O
(	O
released	O
May	O
2006	O
)	O
while	O
the	O
S	O
series	O
supports	O
it	O
out	O
of	O
the	O
box	O
.	O
</s>
<s>
Wii	B-Operating_System
:	O
supports	O
AAC	B-Application
files	I-Application
through	O
version	O
1.1	O
of	O
the	O
Photo	O
Channel	O
as	O
of	O
December	O
11	O
,	O
2007	O
.	O
</s>
<s>
This	O
update	O
removed	O
MP3	B-Application
compatibility	O
,	O
but	O
users	O
who	O
have	O
installed	O
this	O
may	O
freely	O
downgrade	O
to	O
the	O
old	O
version	O
if	O
they	O
wish	O
.	O
</s>
<s>
Livescribe	O
Pulse	O
and	O
Echo	O
Smartpens	O
:	O
record	O
and	O
store	O
audio	O
in	O
AAC	B-Application
format	I-Application
.	O
</s>
<s>
The	O
AAC	B-Application
files	I-Application
are	O
stored	O
in	O
the	O
user	O
's	O
"	O
My	O
Documents	O
"	O
folder	O
of	O
the	O
Windows	B-Application
OS	I-Application
and	O
can	O
be	O
distributed	O
and	O
played	O
without	O
specialized	O
hardware	O
or	O
software	O
from	O
Livescribe	O
.	O
</s>
<s>
Almost	O
all	O
current	O
computer	O
media	B-Device
players	I-Device
include	O
built-in	O
decoders	O
for	O
AAC	O
,	O
or	O
can	O
utilize	O
a	O
library	B-Library
to	O
decode	O
it	O
.	O
</s>
<s>
On	O
Microsoft	B-Application
Windows	I-Application
,	O
DirectShow	B-Library
can	O
be	O
used	O
this	O
way	O
with	O
the	O
corresponding	O
filters	O
to	O
enable	O
AAC	O
playback	O
in	O
any	O
DirectShow	B-Library
based	O
player	O
.	O
</s>
<s>
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
supports	O
AAC	O
via	O
the	O
QuickTime	B-Application
libraries	O
.	O
</s>
<s>
Adobe	B-Operating_System
Flash	I-Operating_System
Player	I-Operating_System
,	O
since	O
version	O
9	O
update	O
3	O
,	O
can	O
also	O
play	O
back	O
AAC	O
streams	O
.	O
</s>
<s>
Since	O
Flash	B-Operating_System
Player	I-Operating_System
is	O
also	O
a	O
browser	O
plugin	O
,	O
it	O
can	O
play	O
AAC	B-Application
files	I-Application
through	O
a	O
browser	O
as	O
well	O
.	O
</s>
<s>
The	O
Rockbox	B-Application
open	B-Application
source	I-Application
firmware	B-Application
(	O
available	O
for	O
multiple	O
portable	O
players	O
)	O
also	O
offers	O
support	O
for	O
AAC	O
to	O
varying	O
degrees	O
,	O
depending	O
on	O
the	O
model	O
of	O
player	O
and	O
the	O
AAC	O
profile	O
.	O
</s>
<s>
Optional	O
iPod	B-Device
support	O
(	O
playback	O
of	O
unprotected	O
AAC	B-Application
files	I-Application
)	O
for	O
the	B-Operating_System
Xbox	I-Operating_System
360	I-Operating_System
is	O
available	O
as	O
a	O
free	O
download	O
from	O
Xbox	B-Application
Live	I-Application
.	O
</s>
<s>
XBMC	B-Application
:	O
supports	O
AAC	O
(	O
both	O
LC	O
and	O
HE	O
)	O
.	O
</s>
<s>
Some	O
of	O
these	O
players	O
(	O
e.g.	O
,	O
foobar2000	B-Application
,	O
Winamp	B-Application
,	O
and	O
VLC	O
)	O
also	O
support	O
the	O
decoding	O
of	O
ADTS	O
(	O
Audio	O
Data	O
Transport	O
Stream	O
)	O
using	O
the	O
SHOUTcast	B-Application
protocol	O
.	O
</s>
<s>
Plug-ins	O
for	O
Winamp	B-Application
and	O
foobar2000	B-Application
enable	O
the	O
creation	O
of	O
such	O
streams	O
.	O
</s>
<s>
In	O
May	O
2006	O
,	O
Nero	O
AG	O
released	O
an	O
AAC	O
encoding	O
tool	O
free	O
of	O
charge	O
,	O
Nero	O
Digital	O
Audio	O
(	O
the	O
AAC	O
codec	B-General_Concept
portion	O
has	O
become	O
Nero	B-Operating_System
AAC	I-Operating_System
Codec	I-Operating_System
)	O
,	O
which	O
is	O
capable	O
of	O
encoding	O
LC-AAC	B-Application
,	O
HE-AAC	O
and	O
HE-AAC	O
v2	O
streams	O
.	O
</s>
<s>
The	O
tool	O
is	O
a	O
Command	B-Application
Line	I-Application
Interface	I-Application
tool	O
only	O
.	O
</s>
<s>
Various	O
tools	O
including	O
the	O
foobar2000	B-Application
audio	O
player	O
and	O
MediaCoder	B-Algorithm
can	O
provide	O
a	O
GUI	B-Application
for	O
this	O
encoder	O
.	O
</s>
<s>
FAAC	B-Operating_System
and	O
FAAD2	B-Operating_System
stand	O
for	O
Freeware	B-Operating_System
Advanced	I-Operating_System
Audio	I-Operating_System
Coder	I-Operating_System
and	O
Decoder	O
2	O
respectively	O
.	O
</s>
<s>
FAAC	B-Operating_System
supports	O
audio	O
object	O
types	O
LC	O
,	O
Main	O
and	O
LTP	O
.	O
</s>
<s>
FAAD2	B-Operating_System
supports	O
audio	O
object	O
types	O
LC	O
,	O
Main	O
,	O
LTP	O
,	O
SBR	B-Algorithm
and	O
PS	O
.	O
</s>
<s>
Although	O
FAAD2	B-Operating_System
is	O
free	B-Application
software	I-Application
,	O
FAAC	B-Operating_System
is	O
not	O
free	B-Application
software	I-Application
.	O
</s>
<s>
A	O
Fraunhofer-authored	O
open-source	B-Application
encoder/decoder	B-General_Concept
included	O
in	O
Android	B-Application
has	O
been	O
ported	O
to	O
other	O
platforms	O
.	O
</s>
<s>
FFmpeg	B-Library
’s	O
native	O
AAC	O
encoder	O
does	O
not	O
support	O
HE-AAC	O
and	O
HE-AACv2	O
,	O
but	O
GPL	O
2.0	O
+	O
of	O
ffmpeg	B-Library
is	O
not	O
compatible	O
with	O
FDK	B-Operating_System
AAC	I-Operating_System
,	O
hence	O
ffmpeg	B-Library
with	O
libfdk-aac	O
is	O
not	O
redistributable	O
.	O
</s>
<s>
The	O
native	O
AAC	O
encoder	O
created	O
in	O
FFmpeg	B-Library
's	O
libavcodec	B-Language
,	O
and	O
forked	O
with	O
Libav	B-Language
,	O
was	O
considered	O
experimental	O
and	O
poor	O
.	O
</s>
<s>
A	O
significant	O
amount	O
of	O
work	O
was	O
done	O
for	O
the	O
3.0	O
release	O
of	O
FFmpeg	B-Library
(	O
February	O
2016	O
)	O
to	O
make	O
its	O
version	O
usable	O
and	O
competitive	O
with	O
the	O
rest	O
of	O
the	O
AAC	O
encoders	O
.	O
</s>
<s>
Libav	B-Language
has	O
not	O
merged	O
this	O
work	O
and	O
continues	O
to	O
use	O
the	O
older	O
version	O
of	O
the	O
AAC	O
encoder	O
.	O
</s>
<s>
These	O
encoders	O
are	O
LGPL-licensed	O
open-source	B-Application
and	O
can	O
be	O
built	O
for	O
any	O
platform	O
that	O
the	O
FFmpeg	B-Library
or	O
Libav	B-Language
frameworks	O
can	O
be	O
built	O
.	O
</s>
<s>
Both	O
FFmpeg	B-Library
and	O
Libav	B-Language
can	O
use	O
the	O
Fraunhofer	B-Operating_System
FDK	I-Operating_System
AAC	I-Operating_System
library	B-Library
via	O
libfdk-aac	O
,	O
and	O
while	O
the	O
FFmpeg	B-Library
native	O
encoder	O
has	O
become	O
stable	O
and	O
good	O
enough	O
for	O
common	O
use	O
,	O
FDK	O
is	O
still	O
considered	O
the	O
highest	O
quality	O
encoder	O
available	O
for	O
use	O
with	O
FFmpeg	B-Library
.	O
</s>
<s>
Libav	B-Language
also	O
recommends	O
using	O
FDK	B-Operating_System
AAC	I-Operating_System
if	O
it	O
is	O
available	O
.	O
</s>
<s>
FFmpeg	B-Library
4.4	O
and	O
above	O
can	O
also	O
use	O
the	O
Apple	O
audiotoolbox	O
encoder	O
.	O
</s>
<s>
Although	O
the	O
native	O
AAC	O
encoder	O
only	O
produces	O
AAC-LC	B-Application
,	O
ffmpeg	B-Library
's	O
native	O
decoder	O
is	O
able	O
to	O
deal	O
with	O
a	O
wide	O
range	O
of	O
input	O
formats	O
.	O
</s>
