<s>
A	O
360	B-General_Concept
video	I-General_Concept
projection	I-General_Concept
is	O
any	O
of	O
many	O
ways	O
to	O
map	O
a	O
spherical	O
field	O
of	O
view	O
to	O
a	O
flat	O
image	O
.	O
</s>
<s>
It	O
is	O
used	O
to	O
encode	O
and	O
deliver	O
the	O
effect	O
of	O
a	O
spherical	O
,	O
360-degree	B-General_Concept
image	O
to	O
viewers	O
such	O
as	O
needed	O
for	O
360-degree	B-General_Concept
videos	I-General_Concept
and	O
for	O
virtual	B-Application
reality	I-Application
.	O
</s>
<s>
A	O
360	B-General_Concept
video	I-General_Concept
projection	I-General_Concept
is	O
a	O
specialized	O
form	O
of	O
a	O
map	B-Application
projection	I-Application
,	O
with	O
characteristics	O
tuned	O
for	O
the	O
efficient	O
representation	O
,	O
transmission	O
,	O
and	O
display	O
of	O
360°	O
fields	O
of	O
view	O
.	O
</s>
<s>
An	O
equirectangular	O
projection	B-Application
simply	O
maps	O
the	O
yaw	O
and	O
pitch	O
(	O
longitude	O
and	O
latitiude	O
)	O
of	O
a	O
sphere	O
linearly	O
to	O
a	O
rectangular	O
image	O
.	O
</s>
<s>
The	O
Equi-Angular	O
Cubemap	O
(	O
EAC	O
)	O
projection	B-Application
is	O
a	O
variant	O
of	O
the	O
cubemap	O
that	O
distributes	O
the	O
pixels	O
evenly	O
by	O
angle	O
.	O
</s>
<s>
It	O
was	O
detailed	O
by	O
Google	B-Application
on	O
March	O
14	O
,	O
2017	O
.	O
</s>
<s>
In	O
January	O
2018	O
the	O
company	O
started	O
using	O
the	O
spherical	B-Application
projection	I-Application
to	O
stream	O
360	O
degree	O
videos	O
on	O
YouTube	B-General_Concept
.	I-General_Concept
</s>
<s>
They	O
noted	O
that	O
EAC	O
enabled	O
then	O
in	O
using	O
25%	O
less	O
pixels	O
by	O
packing	O
the	O
equivalent	O
of	O
5376x2688	O
pixels	O
into	O
an	O
EAC	O
projection	B-Application
of	O
4032x2688	O
pixels	O
.	O
</s>
<s>
This	O
projection	B-Application
was	O
then	O
split	O
horizontally	O
in	O
two	O
streams	O
of	O
4032x1344	O
and	O
encoded	O
,	O
which	O
could	O
be	O
decoded	O
by	O
regular	O
UHD	O
decoders	O
.	O
</s>
<s>
The	O
Pyramid	B-Algorithm
projection	B-Application
is	O
a	O
variation	O
of	O
the	O
cubemap	O
using	O
a	O
pyramid	B-Algorithm
geometry	O
.	O
</s>
<s>
The	O
video	O
is	O
rendered	O
in	O
multiple	O
viewports	O
(	O
in	O
Facebook	O
's	O
case	O
30	O
)	O
where	O
the	O
base	O
of	O
the	O
pyramid	B-Algorithm
contains	O
the	O
full	O
resolution	O
and	O
is	O
right	O
in	O
front	O
of	O
the	O
viewer	O
,	O
while	O
the	O
sides	O
are	O
rendered	O
with	O
a	O
gradually	O
decreasing	O
resolution	O
.	O
</s>
<s>
It	O
was	O
detailed	O
by	O
Facebook	O
on	O
January	O
21	O
,	O
2016	O
,	O
mainly	O
aimed	O
at	O
VR	B-Application
video	O
.	O
</s>
<s>
The	O
company	O
claims	O
an	O
80%	O
reduction	O
in	O
bandwidth	O
with	O
this	O
projection	B-Application
,	O
with	O
the	O
disadvantage	O
that	O
many	O
more	O
viewports	O
need	O
to	O
be	O
rendered	O
and	O
stored	O
.	O
</s>
