[FFmpeg-cvslog] r10438 - trunk/doc/snow.txt
michael
subversion
Sat Sep 8 17:58:45 CEST 2007
Author: michael
Date: Sat Sep 8 17:58:45 2007
New Revision: 10438
Log:
document MC
Modified:
trunk/doc/snow.txt
Modified: trunk/doc/snow.txt
==============================================================================
--- trunk/doc/snow.txt (original)
+++ trunk/doc/snow.txt Sat Sep 8 17:58:45 2007
@@ -55,6 +55,18 @@ header:
max_ref_frames-1 u header_state
qlogs
}
+ if(!keyframe){
+ if(!always_reset)
+ update_mc b header_state
+ if(always_reset || update_mc){
+ for(plane=0; plane<2; plane++){
+ diag_mc b header_state
+ htaps/2-1 u header_state
+ for(i= p->htaps/2; i; i--)
+ |hcoeff[i]| u header_state
+ }
+ }
+ }
spatial_decomposition_type s header_state
qlog s header_state
@@ -155,6 +167,35 @@ max_ref_frames
maximum number of reference frames
this MUST NOT change within a bitstream
+update_mc
+ indicates that motion compensation filter parameters are stored in the
+ header
+
+diag_mc
+ flag to enable faster diagonal interpolation
+ this SHOULD be 1 unless it turns out to be covered by a valid patent
+
+htaps
+ number of half pel interpolation filter taps, MUST be even, >0 and <10
+
+hcoeff
+ half pel interpolation filter coefficients, hcoeff[0] are the 2 middle
+ coefficients [1] are the next outer ones and so on, resulting in a filter
+ like: ...eff[2], hcoeff[1], hcoeff[0], hcoeff[0], hcoeff[1], hcoeff[2] ...
+ the sign of the coefficients is not explicitly stored but alternates
+ after each coeff and coeff[0] is positive, so ...,+,-,+,-,+,+,-,+,-,+,...
+ hcoeff[0] is not explicitly stored but found by subtracting the sum
+ of all stored coefficients with signs from 32
+ hcoeff[0]= 32 - hcoeff[1] - hcoeff[2] - ...
+ a good choice for hcoeff and htaps is
+ htaps= 6
+ hcoeff={40,-10,2}
+ an alternative which requires more computations at both encoder and
+ decoder side and may or may not be better is
+ htaps= 8
+ hcoeff={42,-14,6,-2}
+
+
ref_frames
minimum of the number of available reference frames and max_ref_frames
for example the first frame after a key frame always has ref_frames=1
@@ -234,6 +275,102 @@ block[*][-1].dc[*]= 128;
Motion Compensation:
====================
+
+Halfpel interpolation:
+----------------------
+halfpel interpolation is done by convolution with the halfpel filter stored
+in the header:
+
+horizontal halfpel samples are found by
+H1[y][x] = hcoeff[0]*(F[y][x ] + F[y][x+1])
+ + hcoeff[1]*(F[y][x-1] + F[y][x+2])
+ + hcoeff[2]*(F[y][x-2] + F[y][x+3])
+ + ...
+h1[y][x] = (H1[y][x] + 32)>>6;
+
+vertical halfpel samples are found by
+H2[y][x] = hcoeff[0]*(F[y ][x] + F[y+1][x])
+ + hcoeff[1]*(F[y-1][x] + F[y+2][x])
+ + ...
+h2[y][x] = (H2[y][x] + 32)>>6;
+
+vertical+horizontal halfpel samples are found by
+H3[y][x] = hcoeff[0]*(H2[y][x ] + H2[y][x+1])
+ + hcoeff[1]*(H2[y][x-1] + H2[y][x+2])
+ + ...
+H3[y][x] = hcoeff[0]*(H1[y ][x] + H1[y+1][x])
+ + hcoeff[1]*(H1[y+1][x] + H1[y+2][x])
+ + ...
+h3[y][x] = (H3[y][x] + 2048)>>12;
+
+
+ F H1 F
+ | | |
+ | | |
+ | | |
+ F H1 F
+ | | |
+ | | |
+ | | |
+ F-------F-------F-> H1<-F-------F-------F
+ v v v
+ H2 H3 H2
+ ^ ^ ^
+ F-------F-------F-> H1<-F-------F-------F
+ | | |
+ | | |
+ | | |
+ F H1 F
+ | | |
+ | | |
+ | | |
+ F H1 F
+
+
+unavailable fullpel samples (outside the picture for example) shall be equal
+to the closest available fullpel sample
+
+
+Smaller pel interpolation:
+--------------------------
+if diag_mc is set then points which lie on a line between 2 vertically,
+horiziontally or diagonally adjacent halfpel points shall be interpolated
+linearls with rounding to nearest and halfway values rounded up.
+points which lie on 2 diagonals at the same time should only use the one
+diagonal not containing the fullpel point
+
+
+
+ F-->O---q---O<--h1->O---q---O<--F
+ v \ / v \ / v
+ O O O O O O O
+ | / | \ |
+ q q q q q
+ | / | \ |
+ O O O O O O O
+ ^ / \ ^ / \ ^
+ h2-->O---q---O<--h3->O---q---O<--h2
+ v \ / v \ / v
+ O O O O O O O
+ | \ | / |
+ q q q q q
+ | \ | / |
+ O O O O O O O
+ ^ / \ ^ / \ ^
+ F-->O---q---O<--h1->O---q---O<--F
+
+
+
+the remaining points shall be bilinearly interpolated from the
+up to 4 surrounding halfpel 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
+interpolation at least
+
+
+Overlapped block motion compensation:
+-------------------------------------
FIXME
LL band prediction:
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