description of graphical overlays
---------------------------------

CB - Show Coding Block quadtree structure. Prediction modes are
     signalled at this level. CBs can be further subdivided into
     PBs for prediction and TBs for residual transforms.

PB - Show Prediction Block structure. CB blocks may be further
     subdivided, possibly using asymmetric partitionings. This is
     the level on which motion-compensation and intra-prediction is
     performed.

TB - Show Transformation Block structure. DCT/DSTs are carried out
     on this level.

QP - Quantization Parameter shown as greyscale value.
     Brighter blocks for larger QP values (lower quality).

IntraPred - Show intra prediction mode.
  * Directional prediction is depicted with a line in the prediction direction
    (out of 32 possible directions)
  * Planar prediction is depicted by a square.
  * DC prediction is depicted by a circle.

PredMode - Show prediction mode.
  * red:    intra
  * blue:   inter
  * green:  skip  = inter mode with no PB subdivision and candidate from merge list

MV - Show motion vectors. Vectors from list L0 are drawn in red,
     motion vectors from L1 are green. Vectors are magnified by a factor of 4.