<s>
Variable	B-General_Concept
bitrate	I-General_Concept
(	O
VBR	O
)	O
is	O
a	O
term	O
used	O
in	O
telecommunications	O
and	O
computing	O
that	O
relates	O
to	O
the	O
bitrate	O
used	O
in	O
sound	O
or	O
video	O
encoding	O
.	O
</s>
<s>
As	O
opposed	O
to	O
constant	B-General_Concept
bitrate	I-General_Concept
(	O
CBR	O
)	O
,	O
VBR	O
files	O
vary	O
the	O
amount	O
of	O
output	O
data	O
per	O
time	O
segment	O
.	O
</s>
<s>
The	O
average	O
of	O
these	O
rates	O
can	O
be	O
calculated	O
to	O
produce	O
an	O
average	B-General_Concept
bitrate	I-General_Concept
for	O
the	O
file	O
.	O
</s>
<s>
MP3	B-Application
,	O
WMA	B-Application
and	O
AAC	B-Application
audio	O
files	O
can	O
optionally	O
be	O
encoded	O
in	O
VBR	O
,	O
while	O
Opus	B-Algorithm
and	O
Vorbis	B-Algorithm
are	O
encoded	O
in	O
VBR	O
by	O
default	O
.	O
</s>
<s>
Variable	B-General_Concept
bit	I-General_Concept
rate	I-General_Concept
encoding	O
is	O
also	O
commonly	O
used	O
on	O
MPEG-2	B-Algorithm
video	O
,	O
MPEG-4	B-Application
Part	I-Application
2	I-Application
video	O
(	O
Xvid	B-Algorithm
,	O
DivX	B-Application
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
MPEG-4	O
Part	O
10/H.264	O
video	O
,	O
Theora	B-Algorithm
,	O
Dirac	B-Application
and	O
other	O
video	O
compression	O
formats	O
.	O
</s>
<s>
Additionally	O
,	O
variable	B-General_Concept
rate	I-General_Concept
encoding	I-General_Concept
is	O
inherent	O
in	O
lossless	B-Algorithm
compression	I-Algorithm
schemes	O
such	O
as	O
FLAC	B-Application
and	O
Apple	B-Algorithm
Lossless	I-Algorithm
.	O
</s>
<s>
Single-pass	O
encoding	O
analyzes	O
and	O
encodes	O
the	O
data	O
"	O
on	O
the	O
fly	O
"	O
and	O
it	O
is	O
also	O
used	O
in	O
constant	B-General_Concept
bitrate	I-General_Concept
encoding	O
.	O
</s>
<s>
Single-pass	O
VBR	O
encoding	O
is	O
usually	O
controlled	O
by	O
the	O
fixed	O
quality	O
setting	O
or	O
by	O
the	O
bitrate	O
range	O
(	O
minimum	O
and	O
maximum	O
allowed	O
bitrate	O
)	O
or	O
by	O
the	O
average	B-General_Concept
bitrate	I-General_Concept
setting	O
.	O
</s>
<s>
In	O
a	O
video	O
encoding	O
,	O
two-pass	O
encoding	O
is	O
usually	O
controlled	O
by	O
the	O
average	B-General_Concept
bitrate	I-General_Concept
setting	O
or	O
by	O
the	O
bitrate	O
range	O
setting	O
(	O
minimal	O
and	O
maximal	O
allowed	O
bitrate	O
)	O
or	O
by	O
the	O
target	O
video	O
file	O
size	O
setting	O
.	O
</s>
<s>
Some	O
encoders	O
extend	O
this	O
method	O
with	O
an	O
average	B-General_Concept
bitrate	I-General_Concept
.	O
</s>
<s>
The	O
disadvantage	O
of	O
this	O
method	O
is	O
that	O
the	O
average	B-General_Concept
bitrate	I-General_Concept
(	O
and	O
hence	O
file	O
size	O
)	O
will	O
not	O
be	O
known	O
ahead	O
of	O
time	O
.	O
</s>
<s>
The	O
disadvantage	O
of	O
single	O
pass	O
ABR	O
encoding	O
(	O
with	O
or	O
without	O
Constrained	O
Variable	B-General_Concept
Bitrate	I-General_Concept
)	O
is	O
the	O
opposite	O
of	O
fixed	O
quantizer	O
VBR	O
the	O
size	O
of	O
the	O
output	O
is	O
known	O
ahead	O
of	O
time	O
,	O
but	O
the	O
resulting	O
quality	O
is	O
unknown	O
,	O
although	O
still	O
better	O
than	O
CBR	O
.	O
</s>
<s>
In	O
the	O
first	O
pass	O
,	O
the	O
encoder	O
analyzes	O
the	O
input	O
file	O
and	O
automatically	O
calculates	O
possible	O
bitrate	O
range	O
and/or	O
average	B-General_Concept
bitrate	I-General_Concept
.	O
</s>
