<s>
This	O
article	O
describes	O
audio	O
APIs	O
and	O
components	O
in	O
Microsoft	B-Application
Windows	I-Application
which	O
are	O
now	O
obsolete	O
or	O
deprecated	O
.	O
</s>
<s>
Wave	O
sound	O
events	O
played	O
in	O
Windows	O
(	O
up	O
to	O
Windows	B-Application
XP	I-Application
)	O
and	O
MIDI	O
I/O	O
use	O
MME	O
.	O
</s>
<s>
The	O
devices	O
listed	O
in	O
the	O
Multimedia/Sounds	O
and	O
Audio	O
control	O
panel	O
applet	O
represent	O
the	O
MME	O
API	O
of	O
the	O
sound	B-Device
card	I-Device
driver	O
.	O
</s>
<s>
The	O
Multimedia	O
Extensions	O
(	O
interfaces	O
)	O
were	O
released	O
in	O
autumn	O
1991	O
to	O
support	O
sound	B-Device
cards	I-Device
,	O
as	O
well	O
as	O
CD-ROM	B-Device
drives	O
,	O
which	O
were	O
then	O
becoming	O
increasingly	O
available	O
.	O
</s>
<s>
The	O
Multimedia	O
Extensions	O
were	O
released	O
to	O
Original	O
Equipment	O
Manufacturers	O
(	O
OEMs	O
)	O
,	O
mainly	O
CD-ROM	B-Device
drive	O
and	O
sound	B-Device
card	I-Device
manufacturers	O
,	O
and	O
added	O
basic	O
multimedia	O
support	O
for	O
audio	O
input	O
and	O
output	O
and	O
a	O
CD	O
audio	O
player	O
application	O
to	O
Windows	O
3.0	O
.	O
</s>
<s>
Windows	B-Application
3.1x	I-Application
would	O
later	O
incorporate	O
many	O
of	O
its	O
features	O
.	O
</s>
<s>
Microsoft	O
developed	O
the	O
Windows	O
Sound	O
System	O
sound	B-Device
card	I-Device
specification	O
to	O
complement	O
these	O
extensions	O
.	O
</s>
<s>
But	O
some	O
sound	B-Device
card	I-Device
drivers	O
can	O
emulate	O
more	O
than	O
one	O
MME	O
device	O
(	O
or	O
support	O
more	O
than	O
a	O
single	O
streaming	O
client	O
)	O
so	O
it	O
could	O
work	O
with	O
MME	O
too	O
.	O
</s>
<s>
Starting	O
from	O
Windows	B-Application
XP	I-Application
,	O
MME	O
started	O
to	O
support	O
recording	O
device	O
sharing	O
.	O
</s>
<s>
Prior	O
to	O
Windows	B-Application
XP	I-Application
,	O
the	O
number	O
of	O
MME/WinMM	O
device	O
interfaces	O
(	O
,	O
,	O
midiIn	O
,	O
midiOut	O
,	O
mixer	O
,	O
and	O
aux	O
)	O
is	O
restricted	O
to	O
10	O
.	O
</s>
<s>
This	O
limit	O
is	O
raised	O
from	O
10	O
to	O
32	O
in	O
Windows	B-Application
XP	I-Application
.	O
</s>
<s>
A	O
fault	O
in	O
the	O
MME	O
emulation	O
was	O
introduced	O
in	O
Windows	B-Application
Vista	I-Application
:	O
if	O
sample	O
rate	O
conversion	O
is	O
needed	O
,	O
audible	O
noise	O
is	O
sometimes	O
introduced	O
,	O
such	O
as	O
when	O
playing	O
audio	O
in	O
a	O
web	O
browser	O
that	O
uses	O
these	O
APIs	O
.	O
</s>
<s>
Audio	O
Compression	O
Manager	O
(	O
ACM	O
)	O
is	O
a	O
Windows	O
multimedia	B-Library
framework	I-Library
that	O
manages	O
audio	O
codecs	O
(	O
compressor/decompressors	O
)	O
.	O
</s>
<s>
ACM	O
files	O
can	O
be	O
recognized	O
by	O
their	O
filename	O
extension	O
.acm	B-Device
.	O
</s>
<s>
ACM	O
is	O
considered	O
an	O
outdated	O
framework/API	O
and	O
Microsoft	O
now	O
encourages	O
the	O
use	O
of	O
at	O
least	O
DirectShow	B-Library
.	O
</s>
<s>
However	O
,	O
unlike	O
ACM	O
and	O
the	O
related	O
Video	B-Device
Compression	I-Device
Manager	I-Device
(	O
VCM	O
)	O
,	O
DirectShow	B-Library
provides	O
no	O
means	O
to	O
encode	O
files	O
for	O
end-users	O
but	O
requires	O
developers	O
to	O
build	O
end-to-end	O
graphs	O
for	O
encoding	O
content	O
.	O
</s>
<s>
ACM	O
also	O
does	O
not	O
support	O
VBR	B-General_Concept
audio	O
streams	O
;	O
therefore	O
newer	O
codecs	O
like	O
MPEG-4	B-Application
AAC	I-Application
,	O
Ogg	B-Algorithm
Vorbis	I-Algorithm
,	O
FLAC	B-Application
etc	O
.	O
</s>
<s>
cannot	O
be	O
supported	O
through	O
ACM	O
if	O
using	O
variable	B-General_Concept
bitrates	I-General_Concept
.	O
</s>
<s>
Though	O
many	O
sources	O
state	O
the	O
contrary	O
,	O
Ogg	B-Algorithm
Vorbis	I-Algorithm
does	O
work	O
well	O
with	O
the	O
ACM	O
,	O
e.g.	O
</s>
<s>
when	O
embedded	O
in	O
a	O
RIFF-compatible	O
file	O
(	O
such	O
as	O
a	O
WAV	O
or	O
AVI	O
file	O
as	O
mentioned	O
earlier	O
)	O
,	O
provided	O
the	O
Ogg	B-Algorithm
Vorbis	I-Algorithm
stream	O
is	O
encoded	O
at	O
a	O
constant	O
bitrate	O
.	O
</s>
<s>
KMixer	O
is	O
the	O
Kernel	B-Operating_System
Audio	O
Mixer	O
driver	O
,	O
a	O
part	O
of	O
WDM	B-Application
Audio	O
in	O
Windows	B-Device
98	I-Device
to	O
Windows	B-Application
XP	I-Application
which	O
handles	O
the	O
mixing	O
of	O
multiple	O
sound	O
buffers	O
into	O
an	O
output	O
.	O
</s>
<s>
In	O
Windows	B-Device
98	I-Device
,	O
Windows	O
2000	O
and	O
Windows	B-Device
Me	I-Device
,	O
the	O
KMixer	O
maximum	O
sample	O
rate	O
is	O
100kHz	O
.	O
</s>
<s>
In	O
Windows	B-Application
XP	I-Application
SP1	O
and	O
later	O
,	O
KMixer	O
audio	O
sampling	O
rate	O
supports	O
a	O
maximum	O
of	O
200kHz	O
.	O
</s>
<s>
The	O
KMixer	O
was	O
designed	O
to	O
aid	O
the	O
applications	O
by	O
relieving	O
them	O
from	O
the	O
need	O
to	O
perform	O
the	O
mixing	O
of	O
audio	O
streams	O
,	O
especially	O
on	O
low-end	O
sound	B-Device
cards	I-Device
that	O
did	O
n't	O
support	O
multiple	O
sound	O
streams	O
.	O
</s>
<s>
First	O
,	O
the	O
latency	O
of	O
KMixer	O
is	O
around	O
30	O
ms	O
and	O
it	O
cannot	O
be	O
reduced	O
,	O
because	O
this	O
component	O
sits	O
just	O
right	O
above	O
the	O
port	O
class	O
audio	O
driver	O
,	O
so	O
every	O
audio	O
stream	O
,	O
including	O
those	O
issued	O
by	O
DirectSound	B-Device
(	O
except	O
in	O
cases	O
of	O
hardware	B-General_Concept
mixing	I-General_Concept
)	O
and	O
WinMM	O
,	O
come	O
through	O
the	O
kernel	B-Operating_System
mixer	O
.	O
</s>
<s>
If	O
the	O
audio	O
hardware	O
supports	O
hardware	B-General_Concept
mixing	I-General_Concept
(	O
also	O
known	O
as	O
hardware	O
buffering	O
or	O
DirectSound	B-Device
hardware	B-General_Concept
acceleration	I-General_Concept
)	O
,	O
DirectSound	B-Device
buffers	O
directly	O
to	O
the	O
rendering	O
device	O
.	O
</s>
<s>
Thus	O
,	O
if	O
DirectSound	B-Device
streams	O
use	O
hardware	B-General_Concept
mixing	I-General_Concept
,	O
KMixer	O
is	O
bypassed	O
.	O
</s>
<s>
In	O
earlier	O
releases	O
like	O
the	O
original	O
release	O
of	O
Windows	B-Device
98	I-Device
,	O
KMixer	O
tried	O
to	O
mix	O
every	O
data	O
format	O
that	O
passed	O
through	O
it	O
,	O
even	O
those	O
it	O
did	O
not	O
support	O
.	O
</s>
<s>
It	O
caused	O
various	O
problems	O
with	O
media	O
players	O
that	O
tried	O
to	O
pass	O
AC3-encoded	O
surround	O
sound	O
streams	O
through	O
S/PDIF	O
output	O
of	O
the	O
sound	B-Device
card	I-Device
to	O
an	O
external	O
home	O
cinema	O
receiver	O
.	O
</s>
<s>
This	O
was	O
corrected	O
with	O
Windows	B-Device
Me	I-Device
and	O
provided	O
as	O
a	O
hotfix	O
for	O
Windows	B-Device
98	I-Device
Second	O
Edition	O
and	O
Windows	O
2000	O
SP2	O
.	O
</s>
<s>
Starting	O
with	O
Windows	B-Device
Me	I-Device
,	O
the	O
,	O
DirectSound	B-Device
,	O
and	O
DirectShow	B-Library
APIs	O
support	O
non-PCM	O
formats	O
such	O
as	O
AC-3	O
or	O
WMA	O
over	O
S/PDIF	O
and	O
non-PCM	O
data	O
goes	O
directly	O
to	O
the	O
class	O
driver	O
instead	O
of	O
going	O
through	O
KMixer	O
.	O
</s>
<s>
A	O
new	O
kernel-mode	B-Operating_System
API	O
,	O
Direct	O
Kernel	B-Operating_System
Streaming	O
,	O
was	O
also	O
introduced	O
in	O
Windows	B-Device
98	I-Device
in	O
order	O
to	O
bypass	O
the	O
KMixer	O
and	O
avoid	O
problems	O
associated	O
with	O
it	O
.	O
</s>
<s>
Also	O
,	O
there	O
are	O
many	O
ways	O
to	O
bypass	O
KMixer	O
without	O
the	O
need	O
of	O
an	O
extra	O
plugin	O
to	O
access	O
DirectSound	B-Device
,	O
ASIO	B-Library
,	O
Direct	O
Kernel	B-Operating_System
Streaming	O
or	O
WASAPI	O
.	O
</s>
<s>
In	O
Windows	B-Application
XP	I-Application
,	O
for	O
example	O
,	O
the	O
usage	O
of	O
DirectSound	B-Device
(	O
which	O
Winamp	B-Application
uses	O
by	O
default	O
)	O
with	O
a	O
hardware	O
mixer	O
is	O
a	O
way	O
to	O
bypass	O
KMixer	O
.	O
</s>
<s>
KMixer	O
was	O
removed	O
in	O
Windows	B-Application
Vista	I-Application
.	O
</s>
<s>
It	O
is	O
replaced	O
by	O
the	O
user-mode	B-Operating_System
WASAPI	O
(	O
Windows	O
Audio	O
Session	O
API	O
)	O
Audio	O
Engine	O
which	O
is	O
part	O
of	O
the	O
revamped	O
audio	O
architecture	O
.	O
</s>
<s>
Pre-mixed	O
PCM	B-Algorithm
audio	I-Algorithm
is	O
sent	O
to	O
the	O
driver	O
in	O
a	O
single	O
format	O
(	O
in	O
terms	O
of	O
sample	O
rate	O
,	O
bit	O
depth	O
and	O
channel	O
count	O
)	O
that	O
is	O
configurable	O
from	O
the	O
Sounds	O
control	O
panel	O
.	O
</s>
<s>
WASAPI	O
Exclusive	O
mode	O
bypasses	O
the	O
mixer	O
,	O
as	O
does	O
using	O
third-party	O
audio	O
APIs	O
like	O
OpenAL	B-Application
or	O
ASIO	B-Library
,	O
which	O
still	O
have	O
direct	O
access	O
to	O
the	O
hardware	O
.	O
</s>
<s>
Kernel	B-Operating_System
Streaming	O
or	O
Direct	O
Kernel	B-Operating_System
streaming	O
(	O
Direct	O
KS	O
)	O
is	O
a	O
technique	O
that	O
supports	O
kernel-mode	B-Operating_System
processing	O
of	O
streamed	O
data	O
.	O
</s>
<s>
It	O
enables	O
efficient	O
real-time	O
streaming	O
for	O
multimedia	O
devices	O
such	O
as	O
sound	B-Device
cards	I-Device
and	O
TV	B-Device
tuner	I-Device
cards	I-Device
.	O
</s>
<s>
Kernel	B-Operating_System
streaming	O
allows	O
a	O
device	B-Application
driver	I-Application
to	O
create	O
DirectShow-like	O
filters	O
and	O
pins	O
in	O
kernel	B-Operating_System
mode	O
,	O
providing	O
access	O
to	O
hardware	O
,	O
lower	O
latency	O
communication	O
and	O
still	O
be	O
used	O
within	O
a	O
DirectShow	B-Library
filter	B-Library
graph	I-Library
.	O
</s>
<s>
Kernel	B-Operating_System
streaming	O
was	O
introduced	O
in	O
Windows	B-Device
98	I-Device
.	O
</s>
<s>
When	O
the	O
sound	B-Device
card	I-Device
uses	O
a	O
custom	O
driver	O
for	O
use	O
with	O
the	O
system	O
supplied	O
port	O
class	O
driver	O
PortCls.sys	O
or	O
implements	O
a	O
mini-driver	O
for	O
use	O
with	O
the	O
streaming	O
class	O
driver	O
,	O
applications	O
can	O
bypass	O
the	O
KMixer	O
completely	O
and	O
use	O
the	O
kernel	B-Operating_System
streaming	O
interfaces	O
instead	O
to	O
directly	O
interact	O
with	O
audio	O
driver	O
and	O
reduce	O
latency	O
.	O
</s>
<s>
Windows	B-Device
98	I-Device
includes	O
the	O
first	O
kernel	B-Operating_System
streaming	O
driver	O
,	O
Stream.sys	O
.	O
</s>
<s>
In	O
Windows	B-Application
XP	I-Application
,	O
Microsoft	O
introduced	O
another	O
improved	O
kernel	B-Operating_System
streaming	O
class	O
driver	O
,	O
AVStream	O
.	O
</s>
<s>
Music	O
players	O
such	O
as	O
JRiver	B-Operating_System
Media	I-Operating_System
Center	I-Operating_System
,	O
JPLAY	O
,	O
foobar2000	B-Application
,	O
Audirvana	O
Studio	O
and	O
Winamp	B-Application
support	O
kernel	B-Operating_System
streaming	O
.	O
</s>
<s>
Compared	O
to	O
the	O
regular	O
"	O
WaveOut	O
method	O
"	O
in	O
Microsoft	B-Application
Windows	I-Application
,	O
kernel	B-Operating_System
streaming	O
requires	O
less	O
CPU	B-Device
time	O
.	O
</s>
<s>
Kernel	B-Operating_System
streaming	O
also	O
does	O
not	O
allow	O
device	O
sharing	O
unless	O
kernel-mode	B-Operating_System
audio	O
driver	O
supports	O
multiple	O
clients	O
.	O
</s>
<s>
Prior	O
to	O
Windows	B-Application
Vista	I-Application
,	O
Kernel	B-Operating_System
Streaming	O
offered	O
only	O
a	O
single	O
client-to-driver	O
communication	O
protocol	O
with	O
buffer	O
chain	O
,	O
as	O
used	O
in	O
MME	O
.	O
</s>
<s>
Starting	O
from	O
Vista	B-Application
,	O
new	O
Real-Time	O
Audio	O
(	O
RT	O
Audio	O
,	O
not	O
to	O
be	O
confused	O
with	O
the	O
RTAudio	B-Algorithm
codec	I-Algorithm
)	O
protocol	O
is	O
introduced	O
,	O
based	O
on	O
a	O
single	O
circular	B-Data_Structure
buffer	I-Data_Structure
.	O
</s>
<s>
In	O
Vista	B-Application
and	O
later	O
versions	O
,	O
Audio	O
Subsystem	O
supports	O
both	O
protocols	O
so	O
it	O
can	O
interact	O
with	O
both	O
legacy	O
and	O
new	O
audio	O
drivers	O
.	O
</s>
