<s>
Advanced	B-Application
Systems	I-Application
Format	I-Application
(	O
formerly	O
Advanced	B-Application
Streaming	I-Application
Format	I-Application
,	O
Active	B-Application
Streaming	I-Application
Format	I-Application
)	O
is	O
Microsoft	O
's	O
proprietary	B-Application
digital	O
audio/digital	O
video	O
container	O
format	O
,	O
especially	O
meant	O
for	O
streaming	O
media	O
.	O
</s>
<s>
ASF	O
is	O
part	O
of	O
the	O
Media	B-Device
Foundation	I-Device
framework	O
.	O
</s>
<s>
ASF	O
is	O
based	O
on	O
serialized	B-Application
objects	I-Application
which	O
are	O
essentially	O
byte	B-Application
sequences	O
identified	O
by	O
a	O
GUID	O
marker	O
.	O
</s>
<s>
with	O
which	O
codec	B-General_Concept
)	O
the	O
video	O
or	O
audio	O
should	O
be	O
encoded	O
;	O
it	O
just	O
specifies	O
the	O
structure	O
of	O
the	O
video/audio	O
stream	O
.	O
</s>
<s>
This	O
is	O
similar	O
to	O
the	O
function	O
performed	O
by	O
the	O
QuickTime	B-Application
File	I-Application
Format	I-Application
,	O
AVI	O
,	O
or	O
Ogg	O
formats	O
.	O
</s>
<s>
One	O
of	O
the	O
objectives	O
of	O
ASF	O
was	O
to	O
support	O
playback	O
from	O
digital	O
media	O
servers	O
,	O
HTTP	B-Application
servers	I-Application
,	O
and	O
local	O
storage	O
devices	O
such	O
as	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
The	O
most	O
common	O
media	O
contained	O
within	O
an	O
ASF	B-Application
file	I-Application
are	O
Windows	B-Application
Media	I-Application
Audio	I-Application
(	O
WMA	B-Application
)	O
and	O
Windows	B-Device
Media	I-Device
Video	I-Device
(	O
WMV	B-Device
)	O
.	O
</s>
<s>
The	O
most	O
common	O
file	O
extensions	O
for	O
ASF	B-Application
files	I-Application
are	O
extension	O
(	O
audio-only	O
files	O
using	O
Windows	B-Application
Media	I-Application
Audio	I-Application
,	O
with	O
MIME-type	O
audio/x	O
-ms-wma	O
)	O
and	O
(	O
files	O
containing	O
video	O
,	O
using	O
the	O
Windows	B-Application
Media	I-Application
Audio	I-Application
and	O
Video	O
codecs	B-General_Concept
,	O
with	O
MIME-type	O
video/x	O
-ms-asf	O
)	O
.	O
</s>
<s>
ASF	B-Application
files	I-Application
can	O
also	O
contain	O
objects	B-Language
representing	O
metadata	O
,	O
such	O
as	O
the	O
artist	O
,	O
title	O
,	O
album	O
and	O
genre	O
for	O
an	O
audio	O
track	O
,	O
or	O
the	O
director	O
of	O
a	O
video	O
track	O
,	O
much	O
like	O
the	O
ID3	O
tags	O
of	O
MP3	B-Application
files	I-Application
.	O
</s>
<s>
The	O
ASF	O
container	O
provides	O
the	O
framework	O
for	O
digital	O
rights	O
management	O
in	O
Windows	B-Application
Media	I-Application
Audio	I-Application
and	O
Windows	B-Device
Media	I-Device
Video	I-Device
.	O
</s>
<s>
An	O
analysis	O
of	O
an	O
older	O
scheme	O
used	O
in	O
WMA	B-Application
reveals	O
that	O
it	O
is	O
using	O
a	O
combination	O
of	O
elliptic	O
curve	O
cryptography	O
key	O
exchange	O
,	O
DES	B-Algorithm
block	O
cipher	O
,	O
a	O
custom	O
block	O
cipher	O
,	O
RC4	B-Algorithm
stream	O
cipher	O
and	O
the	O
SHA-1	B-Algorithm
hashing	O
function	O
.	O
</s>
<s>
ASF	O
container-based	O
media	O
are	O
sometimes	O
still	O
streamed	O
on	O
the	O
internet	O
either	O
through	O
the	O
MMS	B-Application
protocol	I-Application
or	O
the	O
RTSP	B-Protocol
protocol	O
.	O
</s>
<s>
Mostly	O
,	O
however	O
,	O
they	O
contain	O
material	O
encoded	O
for	O
'	O
progressive	O
download	O
 '	O
,	O
which	O
can	O
be	O
distributed	O
by	O
any	O
webserver	O
and	O
then	O
offers	O
the	O
same	O
advantages	O
as	O
streaming	O
:	O
the	O
file	O
starts	O
playing	O
as	O
soon	O
as	O
a	O
minimum	O
number	O
of	O
bytes	B-Application
is	O
received	O
and	O
the	O
rest	O
of	O
the	O
download	O
continues	O
in	O
the	O
background	O
while	O
one	O
is	O
watching	O
or	O
listening	O
.	O
</s>
<s>
In	O
2010	O
Google	B-Application
picked	O
RIFF	O
as	O
the	O
container	O
format	O
for	O
WebP	O
.	O
</s>
<s>
The	O
specification	O
is	O
downloadable	O
from	O
the	O
Microsoft	O
website	O
,	O
and	O
the	O
format	O
can	O
be	O
implemented	O
under	O
a	O
license	O
from	O
Microsoft	O
that	O
however	O
does	O
not	O
allow	O
distribution	O
of	O
sources	O
and	O
is	O
not	O
compatible	O
with	O
open	B-Application
source	I-Application
licenses	O
.	O
</s>
<s>
The	O
author	O
of	O
the	O
free	O
software	O
project	O
VirtualDub	B-Application
reported	O
that	O
a	O
Microsoft	O
employee	O
informed	O
him	O
that	O
his	O
software	O
violated	O
a	O
Microsoft	O
patent	O
regarding	O
ASF	O
playback	O
.	O
</s>
<s>
Certain	O
error-correcting	B-Error_Name
techniques	O
related	O
to	O
ASF	O
were	O
patented	O
in	O
the	O
United	O
States	O
(	O
Levi	O
,	O
et	O
al	O
.	O
</s>
