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@ -55,6 +55,18 @@ header: |
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max_ref_frames-1 u header_state |
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qlogs |
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} |
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if(!keyframe){ |
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if(!always_reset) |
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update_mc b header_state |
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if(always_reset || update_mc){ |
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for(plane=0; plane<2; plane++){ |
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diag_mc b header_state |
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htaps/2-1 u header_state |
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for(i= p->htaps/2; i; i--) |
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|hcoeff[i]| u header_state |
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} |
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} |
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} |
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spatial_decomposition_type s header_state |
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qlog s header_state |
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@ -155,6 +167,35 @@ max_ref_frames |
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maximum number of reference frames |
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this MUST NOT change within a bitstream |
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update_mc |
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indicates that motion compensation filter parameters are stored in the |
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header |
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diag_mc |
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flag to enable faster diagonal interpolation |
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this SHOULD be 1 unless it turns out to be covered by a valid patent |
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htaps |
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number of half pel interpolation filter taps, MUST be even, >0 and <10 |
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hcoeff |
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half pel interpolation filter coefficients, hcoeff[0] are the 2 middle |
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coefficients [1] are the next outer ones and so on, resulting in a filter |
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like: ...eff[2], hcoeff[1], hcoeff[0], hcoeff[0], hcoeff[1], hcoeff[2] ... |
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the sign of the coefficients is not explicitly stored but alternates |
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after each coeff and coeff[0] is positive, so ...,+,-,+,-,+,+,-,+,-,+,... |
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hcoeff[0] is not explicitly stored but found by subtracting the sum |
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of all stored coefficients with signs from 32 |
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hcoeff[0]= 32 - hcoeff[1] - hcoeff[2] - ... |
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a good choice for hcoeff and htaps is |
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htaps= 6 |
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hcoeff={40,-10,2} |
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an alternative which requires more computations at both encoder and |
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decoder side and may or may not be better is |
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htaps= 8 |
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hcoeff={42,-14,6,-2} |
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ref_frames |
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minimum of the number of available reference frames and max_ref_frames |
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for example the first frame after a key frame always has ref_frames=1 |
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@ -234,6 +275,102 @@ block[*][-1].dc[*]= 128; |
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Motion Compensation: |
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==================== |
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Halfpel interpolation: |
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---------------------- |
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halfpel interpolation is done by convolution with the halfpel filter stored |
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in the header: |
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horizontal halfpel samples are found by |
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H1[y][x] = hcoeff[0]*(F[y][x ] + F[y][x+1]) |
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+ hcoeff[1]*(F[y][x-1] + F[y][x+2]) |
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+ hcoeff[2]*(F[y][x-2] + F[y][x+3]) |
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+ ... |
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h1[y][x] = (H1[y][x] + 32)>>6; |
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vertical halfpel samples are found by |
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H2[y][x] = hcoeff[0]*(F[y ][x] + F[y+1][x]) |
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+ hcoeff[1]*(F[y-1][x] + F[y+2][x]) |
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+ ... |
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h2[y][x] = (H2[y][x] + 32)>>6; |
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vertical+horizontal halfpel samples are found by |
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H3[y][x] = hcoeff[0]*(H2[y][x ] + H2[y][x+1]) |
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+ hcoeff[1]*(H2[y][x-1] + H2[y][x+2]) |
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+ ... |
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H3[y][x] = hcoeff[0]*(H1[y ][x] + H1[y+1][x]) |
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+ hcoeff[1]*(H1[y+1][x] + H1[y+2][x]) |
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+ ... |
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h3[y][x] = (H3[y][x] + 2048)>>12; |
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F H1 F |
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F H1 F |
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F-------F-------F-> H1<-F-------F-------F |
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v v v |
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H2 H3 H2 |
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^ ^ ^ |
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F-------F-------F-> H1<-F-------F-------F |
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F H1 F |
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F H1 F |
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unavailable fullpel samples (outside the picture for example) shall be equal |
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to the closest available fullpel sample |
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Smaller pel interpolation: |
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-------------------------- |
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if diag_mc is set then points which lie on a line between 2 vertically, |
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horiziontally or diagonally adjacent halfpel points shall be interpolated |
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linearls with rounding to nearest and halfway values rounded up. |
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points which lie on 2 diagonals at the same time should only use the one |
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diagonal not containing the fullpel point |
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F-->O---q---O<--h1->O---q---O<--F |
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v \ / v \ / v |
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O O O O O O O |
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| / | \ | |
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q q q q q |
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| / | \ | |
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O O O O O O O |
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^ / \ ^ / \ ^ |
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h2-->O---q---O<--h3->O---q---O<--h2 |
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v \ / v \ / v |
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O O O O O O O |
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| \ | / | |
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q q q q q |
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| \ | / | |
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O O O O O O O |
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^ / \ ^ / \ ^ |
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F-->O---q---O<--h1->O---q---O<--F |
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the remaining points shall be bilinearly interpolated from the |
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up to 4 surrounding halfpel points, again rounding should be to nearest and |
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halfway values rounded up |
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compliant snow decoders MUST support 1-1/8 pel luma and 1/2-1/16 pel chroma |
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interpolation at least |
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Overlapped block motion compensation: |
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------------------------------------- |
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FIXME |
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LL band prediction: |
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Michael Niedermayer
18 years ago