blob: bbf28bc6c247fc0c3f0bfa079235156a37638cf6
1 | ============================================= |
2 | Snow Video Codec Specification Draft 20080110 |
3 | ============================================= |
4 | |
5 | Introduction: |
6 | ============= |
7 | This specification describes the Snow bitstream syntax and semantics as |
8 | well as the formal Snow decoding process. |
9 | |
10 | The decoding process is described precisely and any compliant decoder |
11 | MUST produce the exact same output for a spec-conformant Snow stream. |
12 | For encoding, though, any process which generates a stream compliant to |
13 | the syntactical and semantic requirements and which is decodable by |
14 | the process described in this spec shall be considered a conformant |
15 | Snow encoder. |
16 | |
17 | Definitions: |
18 | ============ |
19 | |
20 | MUST the specific part must be done to conform to this standard |
21 | SHOULD it is recommended to be done that way, but not strictly required |
22 | |
23 | ilog2(x) is the rounded down logarithm of x with basis 2 |
24 | ilog2(0) = 0 |
25 | |
26 | Type definitions: |
27 | ================= |
28 | |
29 | b 1-bit range coded |
30 | u unsigned scalar value range coded |
31 | s signed scalar value range coded |
32 | |
33 | |
34 | Bitstream syntax: |
35 | ================= |
36 | |
37 | frame: |
38 | header |
39 | prediction |
40 | residual |
41 | |
42 | header: |
43 | keyframe b MID_STATE |
44 | if(keyframe || always_reset) |
45 | reset_contexts |
46 | if(keyframe){ |
47 | version u header_state |
48 | always_reset b header_state |
49 | temporal_decomposition_type u header_state |
50 | temporal_decomposition_count u header_state |
51 | spatial_decomposition_count u header_state |
52 | colorspace_type u header_state |
53 | if (nb_planes > 2) { |
54 | chroma_h_shift u header_state |
55 | chroma_v_shift u header_state |
56 | } |
57 | spatial_scalability b header_state |
58 | max_ref_frames-1 u header_state |
59 | qlogs |
60 | } |
61 | if(!keyframe){ |
62 | update_mc b header_state |
63 | if(update_mc){ |
64 | for(plane=0; plane<nb_plane_types; plane++){ |
65 | diag_mc b header_state |
66 | htaps/2-1 u header_state |
67 | for(i= p->htaps/2; i; i--) |
68 | |hcoeff[i]| u header_state |
69 | } |
70 | } |
71 | update_qlogs b header_state |
72 | if(update_qlogs){ |
73 | spatial_decomposition_count u header_state |
74 | qlogs |
75 | } |
76 | } |
77 | |
78 | spatial_decomposition_type s header_state |
79 | qlog s header_state |
80 | mv_scale s header_state |
81 | qbias s header_state |
82 | block_max_depth s header_state |
83 | |
84 | qlogs: |
85 | for(plane=0; plane<nb_plane_types; plane++){ |
86 | quant_table[plane][0][0] s header_state |
87 | for(level=0; level < spatial_decomposition_count; level++){ |
88 | quant_table[plane][level][1]s header_state |
89 | quant_table[plane][level][3]s header_state |
90 | } |
91 | } |
92 | |
93 | reset_contexts |
94 | *_state[*]= MID_STATE |
95 | |
96 | prediction: |
97 | for(y=0; y<block_count_vertical; y++) |
98 | for(x=0; x<block_count_horizontal; x++) |
99 | block(0) |
100 | |
101 | block(level): |
102 | mvx_diff=mvy_diff=y_diff=cb_diff=cr_diff=0 |
103 | if(keyframe){ |
104 | intra=1 |
105 | }else{ |
106 | if(level!=max_block_depth){ |
107 | s_context= 2*left->level + 2*top->level + topleft->level + topright->level |
108 | leaf b block_state[4 + s_context] |
109 | } |
110 | if(level==max_block_depth || leaf){ |
111 | intra b block_state[1 + left->intra + top->intra] |
112 | if(intra){ |
113 | y_diff s block_state[32] |
114 | cb_diff s block_state[64] |
115 | cr_diff s block_state[96] |
116 | }else{ |
117 | ref_context= ilog2(2*left->ref) + ilog2(2*top->ref) |
118 | if(ref_frames > 1) |
119 | ref u block_state[128 + 1024 + 32*ref_context] |
120 | mx_context= ilog2(2*abs(left->mx - top->mx)) |
121 | my_context= ilog2(2*abs(left->my - top->my)) |
122 | mvx_diff s block_state[128 + 32*(mx_context + 16*!!ref)] |
123 | mvy_diff s block_state[128 + 32*(my_context + 16*!!ref)] |
124 | } |
125 | }else{ |
126 | block(level+1) |
127 | block(level+1) |
128 | block(level+1) |
129 | block(level+1) |
130 | } |
131 | } |
132 | |
133 | |
134 | residual: |
135 | residual2(luma) |
136 | if (nb_planes > 2) { |
137 | residual2(chroma_cr) |
138 | residual2(chroma_cb) |
139 | } |
140 | |
141 | residual2: |
142 | for(level=0; level<spatial_decomposition_count; level++){ |
143 | if(level==0) |
144 | subband(LL, 0) |
145 | subband(HL, level) |
146 | subband(LH, level) |
147 | subband(HH, level) |
148 | } |
149 | |
150 | subband: |
151 | FIXME |
152 | |
153 | nb_plane_types = gray ? 1 : 2; |
154 | |
155 | Tag description: |
156 | ---------------- |
157 | |
158 | version |
159 | 0 |
160 | this MUST NOT change within a bitstream |
161 | |
162 | always_reset |
163 | if 1 then the range coder contexts will be reset after each frame |
164 | |
165 | temporal_decomposition_type |
166 | 0 |
167 | |
168 | temporal_decomposition_count |
169 | 0 |
170 | |
171 | spatial_decomposition_count |
172 | FIXME |
173 | |
174 | colorspace_type |
175 | 0 unspecified YcbCr |
176 | 1 Gray |
177 | 2 Gray + Alpha |
178 | 3 GBR |
179 | 4 GBRA |
180 | this MUST NOT change within a bitstream |
181 | |
182 | chroma_h_shift |
183 | log2(luma.width / chroma.width) |
184 | this MUST NOT change within a bitstream |
185 | |
186 | chroma_v_shift |
187 | log2(luma.height / chroma.height) |
188 | this MUST NOT change within a bitstream |
189 | |
190 | spatial_scalability |
191 | 0 |
192 | |
193 | max_ref_frames |
194 | maximum number of reference frames |
195 | this MUST NOT change within a bitstream |
196 | |
197 | update_mc |
198 | indicates that motion compensation filter parameters are stored in the |
199 | header |
200 | |
201 | diag_mc |
202 | flag to enable faster diagonal interpolation |
203 | this SHOULD be 1 unless it turns out to be covered by a valid patent |
204 | |
205 | htaps |
206 | number of half pel interpolation filter taps, MUST be even, >0 and <10 |
207 | |
208 | hcoeff |
209 | half pel interpolation filter coefficients, hcoeff[0] are the 2 middle |
210 | coefficients [1] are the next outer ones and so on, resulting in a filter |
211 | like: ...eff[2], hcoeff[1], hcoeff[0], hcoeff[0], hcoeff[1], hcoeff[2] ... |
212 | the sign of the coefficients is not explicitly stored but alternates |
213 | after each coeff and coeff[0] is positive, so ...,+,-,+,-,+,+,-,+,-,+,... |
214 | hcoeff[0] is not explicitly stored but found by subtracting the sum |
215 | of all stored coefficients with signs from 32 |
216 | hcoeff[0]= 32 - hcoeff[1] - hcoeff[2] - ... |
217 | a good choice for hcoeff and htaps is |
218 | htaps= 6 |
219 | hcoeff={40,-10,2} |
220 | an alternative which requires more computations at both encoder and |
221 | decoder side and may or may not be better is |
222 | htaps= 8 |
223 | hcoeff={42,-14,6,-2} |
224 | |
225 | |
226 | ref_frames |
227 | minimum of the number of available reference frames and max_ref_frames |
228 | for example the first frame after a key frame always has ref_frames=1 |
229 | |
230 | spatial_decomposition_type |
231 | wavelet type |
232 | 0 is a 9/7 symmetric compact integer wavelet |
233 | 1 is a 5/3 symmetric compact integer wavelet |
234 | others are reserved |
235 | stored as delta from last, last is reset to 0 if always_reset || keyframe |
236 | |
237 | qlog |
238 | quality (logarthmic quantizer scale) |
239 | stored as delta from last, last is reset to 0 if always_reset || keyframe |
240 | |
241 | mv_scale |
242 | stored as delta from last, last is reset to 0 if always_reset || keyframe |
243 | FIXME check that everything works fine if this changes between frames |
244 | |
245 | qbias |
246 | dequantization bias |
247 | stored as delta from last, last is reset to 0 if always_reset || keyframe |
248 | |
249 | block_max_depth |
250 | maximum depth of the block tree |
251 | stored as delta from last, last is reset to 0 if always_reset || keyframe |
252 | |
253 | quant_table |
254 | quantiztation table |
255 | |
256 | |
257 | Highlevel bitstream structure: |
258 | ============================= |
259 | -------------------------------------------- |
260 | | Header | |
261 | -------------------------------------------- |
262 | | ------------------------------------ | |
263 | | | Block0 | | |
264 | | | split? | | |
265 | | | yes no | | |
266 | | | ......... intra? | | |
267 | | | : Block01 : yes no | | |
268 | | | : Block02 : ....... .......... | | |
269 | | | : Block03 : : y DC : : ref index: | | |
270 | | | : Block04 : : cb DC : : motion x : | | |
271 | | | ......... : cr DC : : motion y : | | |
272 | | | ....... .......... | | |
273 | | ------------------------------------ | |
274 | | ------------------------------------ | |
275 | | | Block1 | | |
276 | | ... | |
277 | -------------------------------------------- |
278 | | ------------ ------------ ------------ | |
279 | || Y subbands | | Cb subbands| | Cr subbands|| |
280 | || --- --- | | --- --- | | --- --- || |
281 | || |LL0||HL0| | | |LL0||HL0| | | |LL0||HL0| || |
282 | || --- --- | | --- --- | | --- --- || |
283 | || --- --- | | --- --- | | --- --- || |
284 | || |LH0||HH0| | | |LH0||HH0| | | |LH0||HH0| || |
285 | || --- --- | | --- --- | | --- --- || |
286 | || --- --- | | --- --- | | --- --- || |
287 | || |HL1||LH1| | | |HL1||LH1| | | |HL1||LH1| || |
288 | || --- --- | | --- --- | | --- --- || |
289 | || --- --- | | --- --- | | --- --- || |
290 | || |HH1||HL2| | | |HH1||HL2| | | |HH1||HL2| || |
291 | || ... | | ... | | ... || |
292 | | ------------ ------------ ------------ | |
293 | -------------------------------------------- |
294 | |
295 | Decoding process: |
296 | ================= |
297 | |
298 | ------------ |
299 | | | |
300 | | Subbands | |
301 | ------------ | | |
302 | | | ------------ |
303 | | Intra DC | | |
304 | | | LL0 subband prediction |
305 | ------------ | |
306 | \ Dequantizaton |
307 | ------------------- \ | |
308 | | Reference frames | \ IDWT |
309 | | ------- ------- | Motion \ | |
310 | ||Frame 0| |Frame 1|| Compensation . OBMC v ------- |
311 | | ------- ------- | --------------. \------> + --->|Frame n|-->output |
312 | | ------- ------- | ------- |
313 | ||Frame 2| |Frame 3||<----------------------------------/ |
314 | | ... | |
315 | ------------------- |
316 | |
317 | |
318 | Range Coder: |
319 | ============ |
320 | |
321 | Binary Range Coder: |
322 | ------------------- |
323 | The implemented range coder is an adapted version based upon "Range encoding: |
324 | an algorithm for removing redundancy from a digitised message." by G. N. N. |
325 | Martin. |
326 | The symbols encoded by the Snow range coder are bits (0|1). The |
327 | associated probabilities are not fix but change depending on the symbol mix |
328 | seen so far. |
329 | |
330 | |
331 | bit seen | new state |
332 | ---------+----------------------------------------------- |
333 | 0 | 256 - state_transition_table[256 - old_state]; |
334 | 1 | state_transition_table[ old_state]; |
335 | |
336 | state_transition_table = { |
337 | 0, 0, 0, 0, 0, 0, 0, 0, 20, 21, 22, 23, 24, 25, 26, 27, |
338 | 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42, |
339 | 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 56, 57, |
340 | 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, |
341 | 74, 75, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, |
342 | 89, 90, 91, 92, 93, 94, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, |
343 | 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 114, 115, 116, 117, 118, |
344 | 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 133, |
345 | 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, |
346 | 150, 151, 152, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, |
347 | 165, 166, 167, 168, 169, 170, 171, 171, 172, 173, 174, 175, 176, 177, 178, 179, |
348 | 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 190, 191, 192, 194, 194, |
349 | 195, 196, 197, 198, 199, 200, 201, 202, 202, 204, 205, 206, 207, 208, 209, 209, |
350 | 210, 211, 212, 213, 215, 215, 216, 217, 218, 219, 220, 220, 222, 223, 224, 225, |
351 | 226, 227, 227, 229, 229, 230, 231, 232, 234, 234, 235, 236, 237, 238, 239, 240, |
352 | 241, 242, 243, 244, 245, 246, 247, 248, 248, 0, 0, 0, 0, 0, 0, 0}; |
353 | |
354 | FIXME |
355 | |
356 | |
357 | Range Coding of integers: |
358 | ------------------------- |
359 | FIXME |
360 | |
361 | |
362 | Neighboring Blocks: |
363 | =================== |
364 | left and top are set to the respective blocks unless they are outside of |
365 | the image in which case they are set to the Null block |
366 | |
367 | top-left is set to the top left block unless it is outside of the image in |
368 | which case it is set to the left block |
369 | |
370 | if this block has no larger parent block or it is at the left side of its |
371 | parent block and the top right block is not outside of the image then the |
372 | top right block is used for top-right else the top-left block is used |
373 | |
374 | Null block |
375 | y,cb,cr are 128 |
376 | level, ref, mx and my are 0 |
377 | |
378 | |
379 | Motion Vector Prediction: |
380 | ========================= |
381 | 1. the motion vectors of all the neighboring blocks are scaled to |
382 | compensate for the difference of reference frames |
383 | |
384 | scaled_mv= (mv * (256 * (current_reference+1) / (mv.reference+1)) + 128)>>8 |
385 | |
386 | 2. the median of the scaled left, top and top-right vectors is used as |
387 | motion vector prediction |
388 | |
389 | 3. the used motion vector is the sum of the predictor and |
390 | (mvx_diff, mvy_diff)*mv_scale |
391 | |
392 | |
393 | Intra DC Predicton: |
394 | ====================== |
395 | the luma and chroma values of the left block are used as predictors |
396 | |
397 | the used luma and chroma is the sum of the predictor and y_diff, cb_diff, cr_diff |
398 | to reverse this in the decoder apply the following: |
399 | block[y][x].dc[0] = block[y][x-1].dc[0] + y_diff; |
400 | block[y][x].dc[1] = block[y][x-1].dc[1] + cb_diff; |
401 | block[y][x].dc[2] = block[y][x-1].dc[2] + cr_diff; |
402 | block[*][-1].dc[*]= 128; |
403 | |
404 | |
405 | Motion Compensation: |
406 | ==================== |
407 | |
408 | Halfpel interpolation: |
409 | ---------------------- |
410 | halfpel interpolation is done by convolution with the halfpel filter stored |
411 | in the header: |
412 | |
413 | horizontal halfpel samples are found by |
414 | H1[y][x] = hcoeff[0]*(F[y][x ] + F[y][x+1]) |
415 | + hcoeff[1]*(F[y][x-1] + F[y][x+2]) |
416 | + hcoeff[2]*(F[y][x-2] + F[y][x+3]) |
417 | + ... |
418 | h1[y][x] = (H1[y][x] + 32)>>6; |
419 | |
420 | vertical halfpel samples are found by |
421 | H2[y][x] = hcoeff[0]*(F[y ][x] + F[y+1][x]) |
422 | + hcoeff[1]*(F[y-1][x] + F[y+2][x]) |
423 | + ... |
424 | h2[y][x] = (H2[y][x] + 32)>>6; |
425 | |
426 | vertical+horizontal halfpel samples are found by |
427 | H3[y][x] = hcoeff[0]*(H2[y][x ] + H2[y][x+1]) |
428 | + hcoeff[1]*(H2[y][x-1] + H2[y][x+2]) |
429 | + ... |
430 | H3[y][x] = hcoeff[0]*(H1[y ][x] + H1[y+1][x]) |
431 | + hcoeff[1]*(H1[y+1][x] + H1[y+2][x]) |
432 | + ... |
433 | h3[y][x] = (H3[y][x] + 2048)>>12; |
434 | |
435 | |
436 | F H1 F |
437 | | | | |
438 | | | | |
439 | | | | |
440 | F H1 F |
441 | | | | |
442 | | | | |
443 | | | | |
444 | F-------F-------F-> H1<-F-------F-------F |
445 | v v v |
446 | H2 H3 H2 |
447 | ^ ^ ^ |
448 | F-------F-------F-> H1<-F-------F-------F |
449 | | | | |
450 | | | | |
451 | | | | |
452 | F H1 F |
453 | | | | |
454 | | | | |
455 | | | | |
456 | F H1 F |
457 | |
458 | |
459 | unavailable fullpel samples (outside the picture for example) shall be equal |
460 | to the closest available fullpel sample |
461 | |
462 | |
463 | Smaller pel interpolation: |
464 | -------------------------- |
465 | if diag_mc is set then points which lie on a line between 2 vertically, |
466 | horiziontally or diagonally adjacent halfpel points shall be interpolated |
467 | linearls with rounding to nearest and halfway values rounded up. |
468 | points which lie on 2 diagonals at the same time should only use the one |
469 | diagonal not containing the fullpel point |
470 | |
471 | |
472 | |
473 | F-->O---q---O<--h1->O---q---O<--F |
474 | v \ / v \ / v |
475 | O O O O O O O |
476 | | / | \ | |
477 | q q q q q |
478 | | / | \ | |
479 | O O O O O O O |
480 | ^ / \ ^ / \ ^ |
481 | h2-->O---q---O<--h3->O---q---O<--h2 |
482 | v \ / v \ / v |
483 | O O O O O O O |
484 | | \ | / | |
485 | q q q q q |
486 | | \ | / | |
487 | O O O O O O O |
488 | ^ / \ ^ / \ ^ |
489 | F-->O---q---O<--h1->O---q---O<--F |
490 | |
491 | |
492 | |
493 | the remaining points shall be bilinearly interpolated from the |
494 | up to 4 surrounding halfpel and fullpel points, again rounding should be to |
495 | nearest and halfway values rounded up |
496 | |
497 | compliant Snow decoders MUST support 1-1/8 pel luma and 1/2-1/16 pel chroma |
498 | interpolation at least |
499 | |
500 | |
501 | Overlapped block motion compensation: |
502 | ------------------------------------- |
503 | FIXME |
504 | |
505 | LL band prediction: |
506 | =================== |
507 | Each sample in the LL0 subband is predicted by the median of the left, top and |
508 | left+top-topleft samples, samples outside the subband shall be considered to |
509 | be 0. To reverse this prediction in the decoder apply the following. |
510 | for(y=0; y<height; y++){ |
511 | for(x=0; x<width; x++){ |
512 | sample[y][x] += median(sample[y-1][x], |
513 | sample[y][x-1], |
514 | sample[y-1][x]+sample[y][x-1]-sample[y-1][x-1]); |
515 | } |
516 | } |
517 | sample[-1][*]=sample[*][-1]= 0; |
518 | width,height here are the width and height of the LL0 subband not of the final |
519 | video |
520 | |
521 | |
522 | Dequantizaton: |
523 | ============== |
524 | FIXME |
525 | |
526 | Wavelet Transform: |
527 | ================== |
528 | |
529 | Snow supports 2 wavelet transforms, the symmetric biorthogonal 5/3 integer |
530 | transform and an integer approximation of the symmetric biorthogonal 9/7 |
531 | daubechies wavelet. |
532 | |
533 | 2D IDWT (inverse discrete wavelet transform) |
534 | -------------------------------------------- |
535 | The 2D IDWT applies a 2D filter recursively, each time combining the |
536 | 4 lowest frequency subbands into a single subband until only 1 subband |
537 | remains. |
538 | The 2D filter is done by first applying a 1D filter in the vertical direction |
539 | and then applying it in the horizontal one. |
540 | --------------- --------------- --------------- --------------- |
541 | |LL0|HL0| | | | | | | | | | | | |
542 | |---+---| HL1 | | L0|H0 | HL1 | | LL1 | HL1 | | | | |
543 | |LH0|HH0| | | | | | | | | | | | |
544 | |-------+-------|->|-------+-------|->|-------+-------|->| L1 | H1 |->... |
545 | | | | | | | | | | | | | |
546 | | LH1 | HH1 | | LH1 | HH1 | | LH1 | HH1 | | | | |
547 | | | | | | | | | | | | | |
548 | --------------- --------------- --------------- --------------- |
549 | |
550 | |
551 | 1D Filter: |
552 | ---------- |
553 | 1. interleave the samples of the low and high frequency subbands like |
554 | s={L0, H0, L1, H1, L2, H2, L3, H3, ... } |
555 | note, this can end with a L or a H, the number of elements shall be w |
556 | s[-1] shall be considered equivalent to s[1 ] |
557 | s[w ] shall be considered equivalent to s[w-2] |
558 | |
559 | 2. perform the lifting steps in order as described below |
560 | |
561 | 5/3 Integer filter: |
562 | 1. s[i] -= (s[i-1] + s[i+1] + 2)>>2; for all even i < w |
563 | 2. s[i] += (s[i-1] + s[i+1] )>>1; for all odd i < w |
564 | |
565 | \ | /|\ | /|\ | /|\ | /|\ |
566 | \|/ | \|/ | \|/ | \|/ | |
567 | + | + | + | + | -1/4 |
568 | /|\ | /|\ | /|\ | /|\ | |
569 | / | \|/ | \|/ | \|/ | \|/ |
570 | | + | + | + | + +1/2 |
571 | |
572 | |
573 | Snow's 9/7 Integer filter: |
574 | 1. s[i] -= (3*(s[i-1] + s[i+1]) + 4)>>3; for all even i < w |
575 | 2. s[i] -= s[i-1] + s[i+1] ; for all odd i < w |
576 | 3. s[i] += ( s[i-1] + s[i+1] + 4*s[i] + 8)>>4; for all even i < w |
577 | 4. s[i] += (3*(s[i-1] + s[i+1]) )>>1; for all odd i < w |
578 | |
579 | \ | /|\ | /|\ | /|\ | /|\ |
580 | \|/ | \|/ | \|/ | \|/ | |
581 | + | + | + | + | -3/8 |
582 | /|\ | /|\ | /|\ | /|\ | |
583 | / | \|/ | \|/ | \|/ | \|/ |
584 | (| + (| + (| + (| + -1 |
585 | \ + /|\ + /|\ + /|\ + /|\ +1/4 |
586 | \|/ | \|/ | \|/ | \|/ | |
587 | + | + | + | + | +1/16 |
588 | /|\ | /|\ | /|\ | /|\ | |
589 | / | \|/ | \|/ | \|/ | \|/ |
590 | | + | + | + | + +3/2 |
591 | |
592 | optimization tips: |
593 | following are exactly identical |
594 | (3a)>>1 == a + (a>>1) |
595 | (a + 4b + 8)>>4 == ((a>>2) + b + 2)>>2 |
596 | |
597 | 16bit implementation note: |
598 | The IDWT can be implemented with 16bits, but this requires some care to |
599 | prevent overflows, the following list, lists the minimum number of bits needed |
600 | for some terms |
601 | 1. lifting step |
602 | A= s[i-1] + s[i+1] 16bit |
603 | 3*A + 4 18bit |
604 | A + (A>>1) + 2 17bit |
605 | |
606 | 3. lifting step |
607 | s[i-1] + s[i+1] 17bit |
608 | |
609 | 4. lifiting step |
610 | 3*(s[i-1] + s[i+1]) 17bit |
611 | |
612 | |
613 | TODO: |
614 | ===== |
615 | Important: |
616 | finetune initial contexts |
617 | flip wavelet? |
618 | try to use the wavelet transformed predicted image (motion compensated image) as context for coding the residual coefficients |
619 | try the MV length as context for coding the residual coefficients |
620 | use extradata for stuff which is in the keyframes now? |
621 | implement per picture halfpel interpolation |
622 | try different range coder state transition tables for different contexts |
623 | |
624 | Not Important: |
625 | compare the 6 tap and 8 tap hpel filters (psnr/bitrate and subjective quality) |
626 | spatial_scalability b vs u (!= 0 breaks syntax anyway so we can add a u later) |
627 | |
628 | |
629 | Credits: |
630 | ======== |
631 | Michael Niedermayer |
632 | Loren Merritt |
633 | |
634 | |
635 | Copyright: |
636 | ========== |
637 | GPL + GFDL + whatever is needed to make this a RFC |
638 |