<s>
AMV	O
(	O
Actions	B-Architecture
Media	O
Video	O
)	O
is	O
a	O
proprietary	B-Application
video	O
file	O
format	O
,	O
produced	O
for	O
MP4	O
players	O
,	O
as	O
well	O
as	O
S1	O
MP3	O
players	O
with	O
video	O
playback	O
.	O
</s>
<s>
There	O
are	O
two	O
different	O
versions	O
of	O
this	O
format	O
:	O
an	O
older	O
one	O
for	O
Actions	B-Architecture
chips	O
,	O
and	O
a	O
newer	O
one	O
for	O
ALi	O
’s	O
M5661	O
chip	O
,	O
sometimes	O
called	O
ALIAVI	O
.	O
</s>
<s>
The	O
video	O
format	O
is	O
a	O
variant	O
of	O
Motion	B-Application
JPEG	I-Application
,	O
with	O
fixed	O
rather	O
than	O
variable	O
quantisation	B-Algorithm
tables	O
.	O
</s>
<s>
The	O
audio	O
format	O
is	O
a	O
variant	O
of	O
IMA	B-Algorithm
ADPCM	I-Algorithm
,	O
where	O
the	O
first	O
8	O
bytes	O
of	O
each	O
frame	O
are	O
origin	O
(	O
16	O
bits	O
)	O
,	O
index	O
(	O
16	O
bits	O
)	O
and	O
number	O
of	O
encoded	O
16-bit	O
samples	O
(	O
32	O
bits	O
)	O
;	O
all	O
known	O
AMV	O
files	O
run	O
sound	O
at	O
22050	O
samples/second	O
.	O
</s>
<s>
Low	O
decoder	O
overhead	O
is	O
paramount	O
as	O
the	O
S1	O
MP3	O
players	O
have	O
very	O
low-end	O
processors	O
(	O
a	O
Z80	B-General_Concept
variant	O
)	O
.	O
</s>
<s>
Video	O
compression	O
ratio	O
is	O
low	O
–	O
around	O
4	O
pixels/byte	O
,	O
compared	O
with	O
over	O
10	O
pixels/byte	O
for	O
MPEG-2	B-Algorithm
–	O
though	O
as	O
the	O
files	O
are	O
of	O
low	O
resolution	O
(	O
96×96	O
up	O
to	O
208×176	O
)	O
and	O
frame	O
rate	O
(	O
10	O
,	O
12	O
,	O
or	O
16frame/s	O
)	O
,	O
file	O
sizes	O
are	O
small	O
in	O
bytes	O
per	O
second	O
.	O
</s>
<s>
Documentation	O
for	O
this	O
format	O
is	O
not	O
publicly	O
available	O
,	O
but	O
Dobrica	O
Pavlinušić	O
reverse	O
engineered	O
the	O
format	O
to	O
produce	O
a	O
Perl-based	O
decoder	O
and	O
Pavlinušić	O
,	O
Tom	O
Van	O
Braeckel	O
and	O
Vladimir	O
Voroshilov	O
produced	O
a	O
version	O
of	O
FFmpeg	B-Library
that	O
works	O
on	O
AMV	O
files	O
.	O
</s>
<s>
Fake	O
or	O
cloned	O
iPod	O
Nano	O
(	O
4th	O
generation	O
)	O
devices	O
are	O
reported	O
to	O
only	O
support	O
AMV	B-Algorithm
video	I-Algorithm
formats	I-Algorithm
for	O
video	O
playback	O
.	O
</s>
