10.6 MPEG-2 macroblock header

If the macroblock_address_increment is greater than 1, macroblocks are skipped. Except for the macroblock stuffing code, the MPEG-1 codes given in Table 8.6 are used for macroblock_address_increment. Macroblock stuffing is not allowed in MPEG-2, except in MPEG-1 compatibility mode. Zero stuffing is allowed at slice start code boundaries.

The macroblock_modes() function communicates the macroblock_type data element and extra motion vector related information. It is described in more detail later in this section. If the macroblock_quant_flag is 1 as derived from macroblock_type, then quantiser_scale_code is changed.

     macroblock() {                                /* from ISO 13818--2 6.2.5  */       while (nextbits(11)==`00000001000')         /* while macroblock escape  */         macroblock_escape(11);                    /* r/w '0000 0001 000'      */       macroblock_address_increment(1--11);        /* r/w mb address increment */       macroblock_modes();                     ...