<s>
Google	B-Application
Duo	I-Application
was	O
a	O
proprietary	B-Application
voice	B-Application
over	I-Application
IP	I-Application
(	O
VoIP	B-Application
)	O
and	O
videotelephony	B-Application
service	O
developed	O
by	O
Google	B-Application
,	O
available	O
for	O
Android	B-Application
,	O
iOS	B-Application
and	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
It	O
let	O
users	O
make	O
and	O
receive	O
one-to-one	O
and	O
group	O
audio	O
and	O
video	B-Application
calls	I-Application
with	O
other	O
Duo	B-Application
users	O
in	O
high	O
definition	O
,	O
using	O
end-to-end	O
encryption	O
by	O
default	O
.	O
</s>
<s>
Duo	B-Application
could	O
be	O
used	O
either	O
with	O
a	O
phone	O
number	O
or	O
a	O
Google	B-Application
account	I-Application
,	O
allowing	O
users	O
to	O
call	O
someone	O
from	O
their	O
contact	O
list	O
.	O
</s>
<s>
Google	B-Application
Duo	I-Application
was	O
announced	O
at	O
Google	B-Application
's	I-Application
developer	I-Application
conference	I-Application
on	O
May	O
18	O
,	O
2016	O
,	O
and	O
began	O
its	O
worldwide	O
release	O
on	O
August	O
16	O
,	O
2016	O
.	O
</s>
<s>
Google	B-Application
announced	O
in	O
2022	O
that	O
the	O
service	O
would	O
be	O
merged	O
into	O
Google	B-Protocol
Meet	I-Protocol
,	O
and	O
it	O
was	O
shut	O
down	O
by	O
the	O
end	O
of	O
the	O
year	O
.	O
</s>
<s>
In	O
December	O
2016	O
,	O
Google	B-Application
Duo	I-Application
replaced	O
Hangouts	B-Protocol
within	O
the	O
suite	B-Application
of	I-Application
Google	I-Application
apps	I-Application
device	O
manufacturers	O
must	O
install	O
in	O
order	O
to	O
gain	O
access	O
to	O
the	B-Application
Google	I-Application
Play	O
Store	O
,	O
with	O
Hangouts	B-Protocol
instead	O
becoming	O
optional	O
.	O
</s>
<s>
In	O
August	O
2020	O
,	O
it	O
was	O
reported	O
that	O
Google	B-Application
was	O
planning	O
to	O
eventually	O
merge	O
Google	B-Application
Duo	I-Application
with	O
the	O
business-oriented	O
Google	B-Protocol
Meet	I-Protocol
.	O
</s>
<s>
In	O
December	O
2021	O
this	O
objective	O
had	O
been	O
dropped	O
,	O
but	O
Duo	B-Application
continued	O
to	O
be	O
available	O
and	O
updated	O
.	O
</s>
<s>
In	O
June	O
2022	O
,	O
Google	B-Application
reversed	O
course	O
and	O
announced	O
that	O
Duo	B-Application
and	O
Meet	O
would	O
,	O
in	O
fact	O
,	O
be	O
merged	O
.	O
</s>
<s>
The	O
merger	O
began	O
in	O
August	O
,	O
with	O
the	O
Duo	B-Application
mobile	B-Application
app	I-Application
renamed	O
to	O
Meet	O
and	O
the	O
original	O
Meet	O
app	O
renamed	O
"	O
Meet	O
Original	O
"	O
and	O
scheduled	O
to	O
be	O
phased	O
out	O
.	O
</s>
<s>
The	B-Application
Google	I-Application
Duo	B-Application
web	O
app	O
was	O
redirected	O
to	O
the	B-Application
Google	I-Application
Meet	O
web	O
app	O
.	O
</s>
<s>
Google	B-Application
Duo	I-Application
was	O
optimized	O
for	O
low-bandwidth	O
mobile	O
networks	O
through	O
WebRTC	B-Protocol
and	O
uses	O
QUIC	B-Protocol
over	O
UDP	B-Protocol
.	O
</s>
<s>
For	O
packet	B-Protocol
loss	I-Protocol
concealment	I-Protocol
Duo	B-Application
used	O
WaveNetEQ	O
.	O
</s>
<s>
In	O
February	O
2021	O
,	O
Google	B-Application
announced	O
a	O
new	O
very	O
low-bitrate	O
codec	B-General_Concept
for	O
speech	O
compression	O
called	O
"	O
Lyra	B-Application
"	O
that	O
could	O
operate	O
with	O
network	O
speeds	O
as	O
low	O
as	O
3kbps	O
that	O
avoided	O
robotic	O
voice	O
audio	O
and	O
that	O
was	O
to	O
be	O
rolled	O
out	O
to	O
Duo	B-Application
.	O
</s>
<s>
According	O
to	O
a	O
technical	O
study	O
commissioned	O
by	O
Google	B-Application
from	O
Signals	O
Research	O
Group	O
in	O
2017	O
that	O
compared	O
degradation	O
time	O
over	O
3G	B-Architecture
,	O
LTE	B-Architecture
,	O
and	O
Wi-Fi	O
,	O
Duo	B-Application
provided	O
the	O
highest	O
voice	O
and	O
video	O
quality	O
of	O
any	O
service	O
or	O
app	O
.	O
</s>
<s>
"	O
Knock	O
Knock	O
"	O
showed	O
a	O
live	O
preview	O
of	O
the	O
caller	O
before	O
the	O
recipient	O
picked	O
up	O
,	O
which	O
Google	B-Application
said	O
was	O
to	O
"	O
make	O
calls	O
feel	O
more	O
like	O
an	O
invitation	O
rather	O
than	O
an	O
interruption	O
"	O
.	O
</s>
<s>
In	O
March	O
2017	O
,	O
it	O
was	O
announced	O
that	O
Google	B-Application
Duo	I-Application
would	O
let	O
users	O
make	O
audio-only	O
calls	O
.	O
</s>
<s>
A	O
year	O
later	O
in	O
March	O
2018	O
,	O
video	O
and	O
voice	O
messages	O
were	O
added	O
to	O
Duo	B-Application
.	O
</s>
<s>
Support	O
for	O
eight-person	O
video	B-Application
calls	I-Application
in	O
both	O
the	O
iOS	B-Application
and	O
Android	B-Application
versions	O
of	O
the	O
app	O
was	O
added	O
in	O
May	O
2019	O
.	O
</s>
<s>
In	O
line	O
with	O
similar	O
group	O
calling	O
offerings	O
from	O
FaceTime	B-Operating_System
,	O
WhatsApp	B-Application
,	O
Skype	B-Application
and	O
Facebook	B-Protocol
Messenger	I-Protocol
,	O
participants	O
could	O
join	O
or	O
leave	O
the	O
conversation	O
at	O
any	O
time	O
.	O
</s>
<s>
Google	B-Application
Duo	I-Application
increased	O
maximum	O
group	O
size	O
to	O
twelve	O
at	O
the	O
end	O
of	O
March	O
2020	O
,	O
and	O
to	O
32	O
by	O
May	O
2022	O
.	O
</s>
