Setmotionvectorpredictor () in macroblock. c ()

Reference software jm95, ldecode
In macroblock. C Setmotionvectorpredictor ()

PMV: prediction vector to be obtained.
Ref_frame: Number of the current reference frame, refidxlx
Rframel: The reference frame number of adjacent block A, that is, the standard refidxlxa.
Rframeu: refidxlxb
Rframeur: refidxlxc
Refpic: Reference Frame index of each 4x4 sub-block of the current Encoding Frame.
Tmp_mv: The motion music of each 4x4 sub-block of the current Encoding Frame includes two directions: X and Y.
(The child blocks that have been estimated by motion. The adjacent A, B, C, and D blocks of the current encoding block are all estimated by motion. Therefore, refpic and tmp_mv can be used for reference)
Ref_frame: refer to the frame index number, which is not frame_num or POC number. It is the serial number in the list.
Block_x: coordinates in the X direction
Block_y: Y coordinate
Blockshape_x: the size of the Child block in the X direction, mbpartwidth,
Blockshape_y: the size of the Child block in the Y direction mbpartheight
Mb_x, mb_y = 4 * block_x (block_y) = x + Xs.
Mb_nr = currmbaddr
Rel_x = XD
Block_x = (x + XS)/4?
Blockshape_x = standard predpartwidth
The output of getluma4x4neighbour () is equal to 1/4 of the output of getneighbour, XW/4, YW/4

Call getluma4x4neighbour to calculate block_a, block_ B, block_c, block_d parameters (including validity, address, XW, YW, pos_x, pos_y)

Which situations does block_c not work? (mb_x, mb_y is the coordinate in the XN Macro Block ?)
1.16 × 8, if XN and yn are in the No.1 Macro Block, block_c is invalid (the Macro Block in 16*8, so there is no C Block)
2. mb_x = 0, blcokshape_x = 8, mb_y! = 8, mb_y> 0 (not 0 Macro Block), C is also invalid. (That is, 2nd macro block of 8x8 ?)
3. mb_x = 8, blockshape_x = 8, mb_y! = 0 (the No. 3 macro block of 8x8), and C is invalid.

If C is invalid, replace C with the data of D.
Mvpredtype = 0; (0: MVP, 1: Use A, 2 only use B, 3 only use C)
1. if it is not mbaff: rframel (left) = pos_x of a Macro Block in refpic, pos_y points to the vertex value, rframeu (top) retrieves the value of B macro block points, rframeur (top right) obtain the value of the C macro block.
2. For mbaff:
A) currmb is a field: Then, when rframel is a field, take the value specified by block_x and block_y. If it is a frame, multiply the refidx value by 2, rframeu, and Ur.
B) currmb is a frame. When field a is set, refidx is divided by 2. When frame a is set, block _x and block_y point to the value.

Only when the sequence number of the reference frame of an adjacent block is the same as that of the current reference frame:
Rframel = ref_frame (indicating the serial number of the reference frame = the serial number of the current reference frame)
If the current reference frame only references the same reference frame as a, then mvpredtype = 1. If it is only for B, it is equal to 2. If it is only for C, it is equal to 3;

The following standard p121
1) 8 × 16, 0th macro blocks, and a references the same as currmb references, then mvpredtype = 1
2) 8 × 16, 1st macro blocks, and C references the same as currmb references, then mvpredtype = 3;
3) 16 × 8, 0th macro blocks, and B references the same as currmb references, then mvpredtype = 2
4) 16 × 8, 1st macro blocks, and a references the same as currmb, then mvpredtype = 1;

HV is the parameter for 0, 1 (two cycles) (whether 0 is X, 1 is Y)
1) HV = 0: mv_a, mv_ B, and mv_c both use temp_mv [0].
2) HV = 1:
A) if it is not mbaff: mv_a, mv_ B, and mv_c, use temp_mv [1].
B) For mbaff:
I. currmb is the field: A is the field, mv_a = tmp_mv [1], a is the frame, mv_a = tmp_mv [1]/2, B, C is similar.
Ii. currmb is frame: A is field, mv_a = tmp_mv [1] × 2, A is frame, mv_a = tmp_mv [1]

Different prediction methods are adopted based on mvpredtype:
1) mvpred_median mode: if both B and C are invalid, pred_vec = mv_a; otherwise, pred_vec = mv_a, mv_ B, and mv_c are the intermediate values.
2) mvpred_l mode: pred_vec = mv_a
3) mvpred_u mode: pred_vec = mv_ B;
4) mvpred_ur mode: pred_vec = mv_c;

HV = 0, pmv_x = pred_vec;
HV = 1, pmv_y = pred_vec;