Theo Markettos <theom+n
...@chiark.greenend.org.uk> wrote in
news:fjz*5Puwt@news.chiark.greenend.org.uk:
> Philip Pemberton <phil
...@gmail.com> wrote:
>> Yeah, I found those files kicking around an old RISC OS disc image
>> CD... There's the full ARM ASM source for the YUV decoders, but
>> nothing for Moving Blocks or Moving lines.
>> What I'd really like to find is some details on how Mblks and Mlines
>> work...
> You could always ask Sophie Wilson direct... after all she invented
> them.
> Also have a look at patents... a quick search of the GB database found
> EP0569207 and US5497434 (under Wilson, Alun R.). There may well be
> more, if you poke the various patent databases (she has lots of
> 2000-era architecture stuff under Sophie, including one published last
> Thursday).
I thought that there was documentation out there on how it works...
Anyway, try this. Codecs are always documented in terms of what the
decoder understands - encoding it is a different problem! Moving Blocks
is outright better than Moving Lines.
--Sophie
Definition of the moving blocks data stream
===========================================
The data stream should be considered as a stream of bits with the least
significant bit arriving first. The extracted codes from this stream
construct a new frame from data which may be from the data stream,
or the previous frame. The new frame is constructed as an array of 4x4
pixel blocks, with each pixel block constructed in a number of ways:
* Generate a new 4 x 4 pixel block from data in the stream
* Copy a 4 x 4 pixel block from the previous frame
* Copy a 4 x 4 pixel block from the previous parts of this frame
* Construct a 4 x 4 pixel block in sub-blocks of 2 x 2 pixel blocks. Each
2x 2 pixel block may be a copy previous parts of this frame, or
constructed from data in the stream.
A frame is scanned from top left to bottom right so that when a copy of a
pixel block from this frame is triggered the source must be from existing
pixels. That is, the source must be non-overlapping and above or to the
left of the new block.
A 4 x 4 pixel block of data is supplied in YUV format with 4 x 4 Y values
and 1 x 1 U and V values. The Y, U and V values are each 5 bits long.
This means that 90 bits are supplied for the data in a 4 x 4 pixel block.
A 2 x 2 pixel block of data is supplied in YUV format with 2 x 2 Y values
and 1 x 1 U and V values. The Y, U and V values are each 5 bits long.
This means that 30 bits are supplied for the data in a 2 x 2 pixel block.
A 4 x 4 pixel block copy from the frame being constructed could, in
theory, come from any 4 x 4 area already constructed. In practice it is
only worth providing encodings for close positions. As the source must
not overlap the destination only 8 source positions are provided for:
x offset y offset
2 left 4 up
1 left 4 up
none 4 up
1 right 4 up
2 right 4 up
4 left none up
4 left 1 up
4 left 2 up
Similarly when a 2 x 2 area is being generated by copying from the frame
under construction the following offsets are given encodings:
x offset y offset
2 left 2 up
1 left 2 up
none 2 up
1 right 2 up
2 right 2 up
2 left 1 up
2 left none
3 left none
Here's how the encoding works:
Note: binary numbers are written big endian (ie lsb first). This is show
the bit which is interpreted first to the left so .
At the top level:
1 4 x 4 data
00 4 x 4 move case
01 4 x 4 treated as four 2 x 2 cases
4 x 4 data is encoded as:
YYYYYYYYYYYYYYYYUV
where each Y, U and V is 5 bits. The Ys are supplied in this order:
1 2 3 4
5 6 7 8
9 10 11 12
12 14 15 16
The four 2 x 2 cases are encoded as:
1 2 x 2 data
0 2 x 2 move case
2 x 2 data is encoded as:
YYYYUV
Where each Y, U and V is 5 bits. The Ys are supplied in this order:
1 2
3 4
A move case (both 4 x 4 and 2 x 2) is encoded as follows:
00 temporal copy from same place
01xxx temporal copy from a place where max(x dist, y dist)=1
10xxxx temporal copy from a place where max(x dist, y dist)=2
11xxxxxx temporal copy from a place where max(x dist, y dist)=3 or
4,
OR spacial copy
temporal copy = copy from previous(time) frame.
spacial copy = copy from previous(position) places in current(time)
frame.
[T](x,y) specifies a temporal copy of (x,y) distance
[S](x,y) specifies a spacial copy of (x,y) distance
x < 0 specifies the source is to the left of the destination
y < 0 specifies the source is above the destination
In detail the copies are defined as:
01xxx
0 [T](-1,-1)
1 [T](0,-1)
2 [T](1,-1)
3 [T](-1,0)
4 [T](1,0)
5 [T](-1,1)
6 [T](0,1)
7 [T](1,1)
10xxxx
0 [T](-2,-2)
1 [T](-1,-2)
2 [T](0,-2)
3 [T](1,-2)
4 [T](2,-2)
5 [T](-2,-1)
6 [T](2,-1)
7 [T](-2,0)
8 [T](2,0)
9 [T](-2,1)
10 [T](2,1)
11 [T](-2,2)
12 [T](-1,2)
13 [T](0,2)
14 [T](1,2)
15 [T](2,2)
11xxxxxx
0 [T](-4,-4)
1 [T](-3,-4)
2 [T](-2,-4)
3 [T](-1,-4)
4 [T](0,-4)
5 [T](1,-4)
6 [T](2,-4)
7 [T](3,-4)
8 [T](4,-4)
9 [T](-4,-3)
10 [T](4,-3)
11 [T](-4,2)
12 [T](4,2)
13 [T](-4,1)
14 [T](4,1)
15 [T](-4,0)
16 [T](4,0)
17 [T](-4,1)
18 [T](4,1)
19 [T](-4,2)
20 [T](4,2)
21 [T](-4,3)
22 [T](4,3)
23 [T](-4,4)
24 [T](-3,4)
25 [T](-2,4)
26 [T](-1,4)
27 [T](0,4)
28 [T](1,4)
29 [T](2,4)
30 [T](3,4)
31 [T](4,4)
32 [T](-3,-3)
33 [T](-2,-3)
34 [T](-1,-3)
35 [T](0,-3)
36 [T](1,-3)
37 [T](2,-3)
38 [T](3,-3)
39 [T](-3,-2)
40 [T](3,-2)
41 [T](-3,-1)
42 [T](3,-1)
43 [T](-3,0)
44 [T](3,0)
45 [T](-3,1)
46 [T](3,1)
47 [T](-3,2)
48 [T](3,2)
49 [T](-3,3)
50 [T](-2,3)
51 [T](-1,3)
52 [T](0,3)
53 [T](1,3)
54 [T](2,3)
55 [T](3,3)
4 x 4 case: 2 x 2 case:
56 [S](-2,-4) [S](-2,-2)
57 [S](-1,-4) [S](-1,-2)
58 [S](0,-4) [S](-2,-1)
59 [S](1,-4) [S](0,-2)
60 [S](2,-4) [S](1,-2)
61 [S](-4,0) [S](2,-2)
62 [S](-4,-1) [S](-2,0)
63 [S](-4,-2) [S](-3,0)
