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document MC
Originally committed as revision 10438 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer
parent
61d6e445b1
commit
e9314de600
137
doc/snow.txt
137
doc/snow.txt
@ -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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