<s>
SILK	O
is	O
an	O
audio	O
compression	O
format	O
and	O
audio	B-Algorithm
codec	I-Algorithm
developed	O
by	O
Skype	B-Application
Limited	O
,	O
now	O
a	O
Microsoft	O
subsidiary	O
.	O
</s>
<s>
It	O
was	O
developed	O
for	O
use	O
in	O
Skype	B-Application
,	O
as	O
a	O
replacement	O
for	O
the	O
SVOPC	B-Protocol
codec	O
.	O
</s>
<s>
It	O
has	O
been	O
extended	O
to	O
the	O
Internet	O
standard	O
Opus	B-Algorithm
codec	I-Algorithm
.	O
</s>
<s>
Skype	B-Application
Limited	O
announced	O
that	O
SILK	O
can	O
use	O
a	O
sampling	B-Algorithm
frequency	I-Algorithm
of	O
8	O
,	O
12	O
,	O
16	O
or	O
24kHz	O
and	O
a	O
bit	O
rate	O
from	O
6	O
to	O
40	O
kbit/s	O
.	O
</s>
<s>
The	O
reference	O
implementation	O
is	O
written	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
The	O
codec	O
technology	O
is	O
based	O
on	O
linear	B-Algorithm
predictive	I-Algorithm
coding	I-Algorithm
(	O
LPC	O
)	O
.	O
</s>
<s>
The	O
SILK	O
binary	B-Application
SDK	B-Application
is	O
available	O
.	O
</s>
<s>
The	O
SILK	O
codec	O
is	O
patented	O
and	O
licensed	O
separately	O
from	O
the	O
SILK	O
SDK	B-Application
.	O
</s>
<s>
The	O
codec	O
is	O
open-source	B-License
,	O
freeware	B-License
,	O
available	O
royalty	O
free	O
with	O
restrictions	O
on	O
use	O
and	O
distribution	O
.	O
</s>
<s>
The	O
SDK	B-Application
was	O
initially	O
available	O
only	O
by	O
application	O
by	O
giving	O
details	O
of	O
name	O
,	O
address	O
,	O
phone	O
,	O
and	O
description	O
of	O
how	O
SILK	O
will	O
be	O
used	O
.	O
</s>
<s>
(	O
version	O
1.0.9	O
)	O
the	O
SDK	B-Application
can	O
by	O
downloaded	O
without	O
application	O
,	O
but	O
the	O
licence	O
restricts	O
the	O
use	O
to	O
internal	O
evaluation	O
and	O
testing	O
purposes	O
only	O
,	O
excluding	O
software	O
distribution	O
or	O
use	O
in	O
any	O
commercial	O
product	O
or	O
service	O
.	O
</s>
<s>
SILK	O
replaces	O
the	O
previously	O
used	O
SVOPC	B-Protocol
in	O
Skype	B-Application
,	O
which	O
was	O
a	O
in-house	O
solution	O
to	O
replace	O
the	O
iSAC	B-Algorithm
and	O
iLBC	B-Algorithm
,	O
which	O
again	O
were	O
licensed	O
from	O
Global	B-Application
IP	I-Application
Solutions	I-Application
.	O
</s>
<s>
The	O
SILK	O
codec	O
was	O
a	O
separate	O
development	O
branch	O
from	O
SVOPC	B-Protocol
and	O
it	O
has	O
been	O
under	O
development	O
for	O
over	O
3	O
years	O
.	O
</s>
<s>
It	O
was	O
announced	O
in	O
January	O
2009	O
on	O
the	O
Consumer	O
Electronics	O
Show	O
and	O
was	O
integrated	O
in	O
Skype	B-Application
for	O
the	O
first	O
time	O
in	O
version	O
4.0	O
beta	O
3	O
from	O
January	O
7	O
,	O
2009	O
,	O
with	O
the	O
final	O
version	O
being	O
released	O
on	O
February	O
3	O
.	O
</s>
<s>
On	O
March	O
3	O
,	O
2009	O
Skype	B-Application
Limited	O
announced	O
that	O
the	O
SILK	O
codec	O
will	O
be	O
available	O
soon	O
under	O
a	O
royalty	O
free	O
license	O
to	O
third-party	O
software	O
and	O
hardware	O
developers	O
.	O
</s>
<s>
The	O
first	O
draft	O
of	O
the	O
SILK	O
Speech	O
Codec	O
description	O
was	O
submitted	O
to	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
as	O
a	O
candidate	O
for	O
the	O
standardisation	O
of	O
a	O
new	O
Internet	O
wideband	O
audio	B-Algorithm
codec	I-Algorithm
on	O
July	O
6	O
,	O
2009	O
,	O
thereby	O
openly	O
publishing	O
the	O
format	O
along	O
with	O
the	O
source	O
code	O
of	O
the	O
reference	O
implementation	O
.	O
</s>
<s>
There	O
is	O
also	O
a	O
first	O
draft	O
of	O
the	O
RTP	B-Protocol
Payload	O
Format	O
and	O
File	O
Storage	O
Format	O
for	O
SILK	O
Speech	O
and	O
Audio	B-Algorithm
Codec	I-Algorithm
.	O
</s>
<s>
SILK	O
is	O
a	O
foundation	O
(	O
with	O
CELT	B-Algorithm
)	O
of	O
the	O
hybrid	O
codec	O
Opus	B-Algorithm
(	O
at	O
the	O
time	O
called	O
"	O
Harmony	O
"	O
)	O
that	O
was	O
submitted	O
to	O
the	O
IETF	O
in	O
September	O
2010	O
,	O
and	O
was	O
chosen	O
as	O
the	O
final	O
candidate	O
for	O
the	O
new	O
standard	O
.	O
</s>
<s>
Opus	B-Algorithm
was	O
published	O
as	O
an	O
IETF	O
proposed	O
standard	O
in	O
September	O
2012	O
.	O
</s>
<s>
The	O
stable	O
version	O
of	O
SILK	O
was	O
first	O
introduced	O
in	O
Skype	B-Application
4.0	O
Beta	O
3	O
for	O
Windows	O
,	O
released	O
on	O
January	O
7	O
,	O
2009	O
.	O
</s>
<s>
The	O
final	O
version	O
of	O
Skype	B-Application
4.0	O
was	O
released	O
on	O
February	O
3	O
,	O
2009	O
.	O
</s>
<s>
On	O
March	O
22	O
,	O
2011	O
the	O
Steam	B-Application
game	I-Application
platform	I-Application
started	O
using	O
the	O
SILK	O
codec	O
for	O
its	O
integrated	O
in-game	O
and	O
community	O
voice	O
chat	O
.	O
</s>
<s>
Later	O
in	O
14	O
April	O
,	O
in	O
Team	B-Application
Fortress	I-Application
2	I-Application
,	O
the	O
codec	O
was	O
implemented	O
into	O
the	O
in-game	O
voice	O
chat	O
.	O
</s>
<s>
On	O
January	O
29	O
,	O
2013	O
the	O
updated	O
to	O
SteamPipe	O
platform	O
Gold	B-Application
Source	I-Application
started	O
using	O
the	O
SILK	O
codec	O
for	O
the	O
in-game	O
voice	O
chat	O
.	O
</s>
<s>
It	O
has	O
been	O
found	O
being	O
used	O
on	O
Zoom	B-Application
.	O
</s>
