text_src/a.03_vp8-bitstream__mb_header.txt

#### A.3 Macroblock Data                                   {#h-0a-03}


| ---------------------------------------------- | ----- |
| Macroblock Data                                | Type  |
| ---------------------------------------------- | ----- |
| macroblock_header()                            |       |
| residual_data()                                |       |
{:.col1-pre}


| ---------------------------------------------- | ----- |
| macroblock_header()                            | Type  |
| ---------------------------------------------- | ----- |
| if (update_mb_segmentation_map)                |       |
|   segment_id                                   | T     |
| if (mb_no_skip_coeff)                          |       |
|   mb_skip_coeff                                | B(p)  |
| if (!key_frame)                                |       |
|   is_inter_mb                                  | B(p)  |
| if (is_inter_mb) {                             |       |
|   mb_ref_frame_sel1                            | B(p)  |
|   if (mb_ref_frame_sel1)                       |       |
|     mb_ref_frame_sel2                          | B(p)  |
|   mv_mode                                      | T     |
|   if (mv_mode == SPLITMV) {                    |       |
|     mv_split_mode                              | T     |
|     for (i = 0; i < numMvs; i++) {             |       |
|       sub_mv_mode                              | T     |
|       if (sub_mv_mode == NEWMV4x4) {           |       |
|         read_mvcomponent()                     |       |
|         read_mvcomponent()                     |       |
|       }                                        |       |
|    }                                           |       |
|   } else if (mv_mode == NEWMV) {               |       |
|     read_mvcomponent()                         |       |
|     read_mvcomponent()                         |       |
|   }                                            |       |
| } else { /* intra mb */                        |       |
|   intra_y_mode                                 | T     |
|   if (intra_y_mode == B_PRED) {                |       |
|     for (i = 0; i < 16; i++)                   |       |
|       intra_b_mode                             | T     |
|   }                                            |       |
|   intra_uv_mode                                | T     |
| }                                              |       |
{:.col1-pre}


  * `segment_id` indicates to which segment the macroblock belongs
    ([Section 10](#h-10-00))

  * `mb_skip_coeff` indicates whether the macroblock contains any coded
    coefficients or not ([Section 11.1](#h-11-01))

  * `is_inter_mb` indicates whether the macroblock is intra- or inter-
    coded ([Section 16](#h-16-00))

  * `mb_ref_frame_sel1` selects the reference frame to be used; last
    frame (0), golden/alternate (1) ([Section 16.2](#h-16-02))

  * `mb_ref_frame_sel2` selects whether the golden (0) or alternate
    reference frame (1) is used ([Section 16.2](#h-16-02))

  * `mv_mode` determines the macroblock motion vector mode
    ([Section 16.2](#h-16-02))

  * `mv_split_mode` gives the macroblock partitioning specification and
    determines the number of motion vectors used (numMvs)
    ([Section 16.2](#h-16-02))

  * `sub_mv_mode` determines the sub-macroblock motion vector mode for
    macroblocks coded using the `SPLITMV` motion vector mode
    ([Section 16.2](#h-16-02))

  * `intra_y_mode` selects the luminance intra-prediction mode
    ([Section 16.1](#h-16-01))

  * `intra_b_mode` selects the sub-macroblock luminance prediction mode
    for macroblocks coded using `B_PRED` mode ([Section 16.1](#h-16-01))

  * `intra_uv_mode` selects the chrominance intra-prediction mode
    ([Section 16.1](#h-16-01))


| ----------------------------------------------------- | ----- |
| residual_data()                                       | Type  |
| ----------------------------------------------------- | ----- |
| if (!mb_skip_coeff) {                                 |       |
|   if ( (is_inter_mb && mv_mode != SPLITMV) ||         |       |
|        (!is_inter_mb && intra_y_mode != B_PRED) )     |       |
|     residual_block() /* Y2 */                         |       |
|   for (i = 0; i < 24; i++)                            |       |
|     residual_block() /* 16 Y, 4 U, 4 V */             |       |
| }                                                     |       |
{:.col1-pre}


| ----------------------------------------------------- | ----- |
| residual_block()                                      | Type  |
| ----------------------------------------------------- | ----- |
| for (i = firstCoeff; i < 16; i++) {                   |       |
|   token                                               |   T   |
|   if (token == EOB) break;                            |       |
|   if (token_has_extra_bits)                           |       |
|     extra_bits                                        | L(n)  |
|   if (coefficient != 0)                               |       |
|   sign                                                | L(1)  |
| }                                                     |       |
{:.col1-pre}


  * firstCoeff is 1 for luma blocks of macroblocks containing Y2
    subblock; otherwise 0

  * `token` defines the value of the coefficient, the value range of the
    coefficient, or the end of block ([Section 13.2](#h-13-02))

  * `extra_bits` determines the value of the coefficient within the
    value range defined by the `token` ([Section 13.2](#h-13-02))

  * `sign` indicates the sign of the coefficient ([Section 13.2](#h-13-02))