[xiph-commits] r17256 - experimental/derf/theora-ptalarbvorm/doc/spec

[tterribe at svn.xiph.org]

Author: tterribe
Date: 2010-05-29 16:38:46 -0700 (Sat, 29 May 2010)
New Revision: 17256

Modified:
   experimental/derf/theora-ptalarbvorm/doc/spec/spec.tex
Log:
Fix the expository text in Macro Block Motion Vector Decode.
It did not agree with the step-by-step procedure below it in the case of
 propagating LAST and LAST2 MVs from INTER_MV_FOUR MBs with some of the luma
 blocks uncoded.
The step-by-step procedure was correct.
Reported by Simon Hosie.


Modified: experimental/derf/theora-ptalarbvorm/doc/spec/spec.tex
===================================================================
--- experimental/derf/theora-ptalarbvorm/doc/spec/spec.tex	2010-05-29 14:53:16 UTC (rev 17255)
+++ experimental/derf/theora-ptalarbvorm/doc/spec/spec.tex	2010-05-29 23:38:46 UTC (rev 17256)
@@ -4094,14 +4094,15 @@
 For INTER\_MV and INTER\_GOLDEN\_MV modes, a single motion vector is decoded
  and applied to each block.
 For INTER\_MV\_FOUR macro blocks, a motion vector is decoded for each coded
- luma block.
+ luma block, in raster order, not coded order.
 Uncoded luma blocks receive the default $(0,0)$ vector for the purposes of
  computing the chroma motion vectors.
 
 None of the remaining macro block coding modes require decoding motion vectors
  from the stream.
-INTRA mode does not use a motion-compensated predictor, and so requires no
- motion vector, and INTER\_NOMV and INTER\_GOLDEN\_NOMV modes use the default
+INTRA mode does not use a motion-compensated predictor, and thus does not
+ require a motion vector.
+Both the INTER\_NOMV and the INTER\_GOLDEN\_NOMV modes use the default
  vector $(0,0)$ for each block.
 This also includes all macro blocks with no coded luma blocks, as they are
  coded in INTER\_NOMV mode by definition.
@@ -4112,10 +4113,12 @@
 Thus no explicit motion vector needs to be decoded for these modes.
 Macro blocks coded in INTRA mode or one of the GOLDEN modes are not considered
  in this process.
+For macro blocks coded in INTER\_MV\_FOUR mode, this process uses the vector
+ from the last coded luma block in the macro block, again in raster order, not
+ coded order.
+This is usually the upper-right block.
 If an insufficient number of macro blocks have been coded in one of the INTER
  modes, then the $(0,0)$ vector is used instead.
-For macro blocks coded in INTER\_MV\_FOUR mode, the vector from the upper-right
- luma block is used, even if the upper-right block is not coded.
 
 The motion vectors are decoded from the stream as follows: