=============================================
-SNOW Video Codec Specification Draft 20070103
+Snow Video Codec Specification Draft 20080110
=============================================
-Intro:
-======
-This Specification describes the snow syntax and semmantics as well as
-how to decode snow.
-The decoding process is precissely described and any compliant decoder
-MUST produce the exactly same output for a spec conformant snow stream.
-For encoding though any process which generates a stream compliant to
-the syntactical and semmantical requirements and which is decodeable by
+Introduction:
+=============
+This specification describes the Snow bitstream syntax and semantics as
+well as the formal Snow decoding process.
+
+The decoding process is described precisely and any compliant decoder
+MUST produce the exact same output for a spec-conformant Snow stream.
+For encoding, though, any process which generates a stream compliant to
+the syntactical and semantic requirements and which is decodable by
the process described in this spec shall be considered a conformant
-snow encoder.
+Snow encoder.
Definitions:
============
block(0)
block(level):
+ mvx_diff=mvy_diff=y_diff=cb_diff=cr_diff=0
if(keyframe){
intra=1
- y_diff=cb_diff=cr_diff=0
}else{
if(level!=max_block_depth){
s_context= 2*left->level + 2*top->level + topleft->level + topright->level
residual:
+ residual2(luma)
+ residual2(chroma_cr)
+ residual2(chroma_cb)
+
+residual2:
+ for(level=0; level<spatial_decomposition_count; level++){
+ if(level==0)
+ subband(LL, 0)
+ subband(HL, level)
+ subband(LH, level)
+ subband(HH, level)
+ }
+
+subband:
FIXME
quant_table
quantiztation table
+
+Highlevel bitstream structure:
+=============================
+ --------------------------------------------
+| Header |
+ --------------------------------------------
+| ------------------------------------ |
+| | Block0 | |
+| | split? | |
+| | yes no | |
+| | ......... intra? | |
+| | : Block01 : yes no | |
+| | : Block02 : ....... .......... | |
+| | : Block03 : : y DC : : ref index: | |
+| | : Block04 : : cb DC : : motion x : | |
+| | ......... : cr DC : : motion y : | |
+| | ....... .......... | |
+| ------------------------------------ |
+| ------------------------------------ |
+| | Block1 | |
+| ... |
+ --------------------------------------------
+| ------------ ------------ ------------ |
+|| Y subbands | | Cb subbands| | Cr subbands||
+|| --- --- | | --- --- | | --- --- ||
+|| |LL0||HL0| | | |LL0||HL0| | | |LL0||HL0| ||
+|| --- --- | | --- --- | | --- --- ||
+|| --- --- | | --- --- | | --- --- ||
+|| |LH0||HH0| | | |LH0||HH0| | | |LH0||HH0| ||
+|| --- --- | | --- --- | | --- --- ||
+|| --- --- | | --- --- | | --- --- ||
+|| |HL1||LH1| | | |HL1||LH1| | | |HL1||LH1| ||
+|| --- --- | | --- --- | | --- --- ||
+|| --- --- | | --- --- | | --- --- ||
+|| |HH1||HL2| | | |HH1||HL2| | | |HH1||HL2| ||
+|| ... | | ... | | ... ||
+| ------------ ------------ ------------ |
+ --------------------------------------------
+
+Decoding process:
+=================
+
+ ------------
+ | |
+ | Subbands |
+ ------------ | |
+ | | ------------
+ | Intra DC | |
+ | | LL0 subband prediction
+ ------------ |
+ \ Dequantizaton
+ ------------------- \ |
+| Reference frames | \ IDWT
+| ------- ------- | Motion \ |
+||Frame 0| |Frame 1|| Compensation . OBMC v -------
+| ------- ------- | --------------. \------> + --->|Frame n|-->output
+| ------- ------- | -------
+||Frame 2| |Frame 3||<----------------------------------/
+| ... |
+ -------------------
+
+
Range Coder:
============
+
+Binary Range Coder:
+-------------------
+The implemented range coder is an adapted version based upon "Range encoding:
+an algorithm for removing redundancy from a digitised message." by G. N. N.
+Martin.
+The symbols encoded by the Snow range coder are bits (0|1). The
+associated probabilities are not fix but change depending on the symbol mix
+seen so far.
+
+
+bit seen | new state
+---------+-----------------------------------------------
+ 0 | 256 - state_transition_table[256 - old_state];
+ 1 | state_transition_table[ old_state];
+
+state_transition_table = {
+ 0, 0, 0, 0, 0, 0, 0, 0, 20, 21, 22, 23, 24, 25, 26, 27,
+ 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42,
+ 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 56, 57,
+ 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73,
+ 74, 75, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88,
+ 89, 90, 91, 92, 93, 94, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103,
+104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 114, 115, 116, 117, 118,
+119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 133,
+134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149,
+150, 151, 152, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164,
+165, 166, 167, 168, 169, 170, 171, 171, 172, 173, 174, 175, 176, 177, 178, 179,
+180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 190, 191, 192, 194, 194,
+195, 196, 197, 198, 199, 200, 201, 202, 202, 204, 205, 206, 207, 208, 209, 209,
+210, 211, 212, 213, 215, 215, 216, 217, 218, 219, 220, 220, 222, 223, 224, 225,
+226, 227, 227, 229, 229, 230, 231, 232, 234, 234, 235, 236, 237, 238, 239, 240,
+241, 242, 243, 244, 245, 246, 247, 248, 248, 0, 0, 0, 0, 0, 0, 0};
+
FIXME
+
+Range Coding of integers:
+-------------------------
+FIXME
+
+
Neighboring Blocks:
===================
left and top are set to the respective blocks unless they are outside of
the used luma and chroma is the sum of the predictor and y_diff, cb_diff, cr_diff
to reverse this in the decoder apply the following:
-block[y][x].dc[0] += block[y][x-1].dc[0];
-block[y][x].dc[1] += block[y][x-1].dc[1];
-block[y][x].dc[2] += block[y][x-1].dc[2];
+block[y][x].dc[0] = block[y][x-1].dc[0] + y_diff;
+block[y][x].dc[1] = block[y][x-1].dc[1] + cb_diff;
+block[y][x].dc[2] = block[y][x-1].dc[2] + cr_diff;
block[*][-1].dc[*]= 128;
up to 4 surrounding halfpel and fullpel points, again rounding should be to
nearest and halfway values rounded up
-compliant snow decoders MUST support 1-1/8 pel luma and 1/2-1/16 pel chroma
+compliant Snow decoders MUST support 1-1/8 pel luma and 1/2-1/16 pel chroma
interpolation at least
| + | + | + | + +1/2
-snows 9/7 Integer filter:
+Snow's 9/7 Integer filter:
1. s[i] -= (3*(s[i-1] + s[i+1]) + 4)>>3; for all even i < w
2. s[i] -= s[i-1] + s[i+1] ; for all odd i < w
3. s[i] += ( s[i-1] + s[i+1] + 4*s[i] + 8)>>4; for all even i < w
projects / ffmpeg / blobdiff