[Mp4-tech] time_scale and num_units in tick: what am I missing?

[John Cox]

Hi
Without exhaustively checking your working my guess is that you haven't
dealt with the emulation prevention.  The byte sequence 00 00 03 needs
to have the 03 stripped out before you parse it (see sections 7.3.1 &
7.4.1 in the standard).
John Cox
SJ Consulting
>Okay, so I'm having trouble parsing a seq_parameter_set_rbsp which contains 
>vui_parameters, so I'm getting lost in the following bits.  Everything I 
>compute agrees with another program up to the timing info.  Here's the MPEG-2 
>transport stream packet:
>
>47 41 2c 39 01 60 00 00 01 e0 00 00 82 c0 0a 31 
>57 e1 5a 21 11 57 e1 3e 01 00 00 00 01 09 10 00 
>00 00 01 67 4d 40 1e 89 99 82 c1 22 c1 bd c1 41 
>41 7c 00 00 03 00 04 00 00 03 00 ca 10 00 00 00 
>01 68 ea 88 35 c8 00 00 00 01 65 b8 00 20 00 af 
>fe d4 a7 99 63 a3 da 16 1b c2 4b b2 86 de 8f 0d 
>58 fb 4f 60 9e b0 8e 20 00 00 24 b0 8c 91 50 b2 
>7e 90 54 df 21 13 74 7d c0 0b 09 8a 95 d5 81 d5 
>8a 32 04 0e a7 35 bb 21 06 9f af 00 02 fe 72 88 
>05 7c ac 89 0f b0 68 3e 80 a6 cf 3b 8a 47 87 d6 
>4f 1d b4 8d 39 43 72 d0 d7 11 a2 63 55 9a fd 53 
>ff e9 68 23 e9 5b 91 7c d3 31 b0 f7             .
>
>which has a PES header (00 00 01 e0), an AU delimiter (00 00 01 09) and then 
>the 26-bytes of the SEQ following the 00 00 01 67:
>
>4d 40 1e 89 99 82 c1 22 c1 bd c1 41 41 7c 00 00 03 00 04 00 00 03 00 ca 10 00
>
>Here's my parse, by HAND of this, which agrees with my code.  And agrees with 
>this other program up to the timing info.  Oh, by the way, its a PAL sample 
>(25fps):
>
>00: 4d  0100 1101
>01: 40  0100 0000
>02: 1e  0001 1110
>03: 89  1000 1001
>04: 99  1001 1001
>05: 82  1000 0010
>06: c1  1100 0001
>07: 22  0010 0010
>08: c1  1100 0001
>09: bd  1011 1101
>10: c1  1100 0001
>11: 41  0100 0001
>12: 41  0100 0001
>13: 7c  0111 1100
>14: 00  0000 0000
>15: 00  0000 0000
>16: 03  0000 0011
>17: 00  0000 0000
>18: 04  0000 0100
>19: 00  0000 0000
>20: 00  0000 0000
>21: 03  0000 0011
>22: 00  0000 0000
>23: ca  1100 1010
>24: 10  0001 0000
>25: 00  0000 0000
>
>[ 01001101 ]  profile_idc = 77			// u(8)
>[ 0100 ] CF0 = 0 CF1 = 1 CF2 = 0 CF3 = 0	// u(1) u(1) u(1) u(1)
>[ 0000 ] Reserved					// u(4)
>[ 00011110 ] level_idc = 30				// u(8)
>[ 1 ] seq_parameter_set_id = 0			// ue(v)
>[ 0001001 ] log2_max_frame_num_minus4 = 8(12) // ue(v)
>[ 1 ] pic_order_cnt_type = 0			// ue(v)
>[ 00110 ] log2_max_pic_order_cnt_lsb_minus4 = 5(9) // ue(v)
>[ 011 ] num_ref_frames = 2				// ue(v)
>[ 0 ] gaps_in_frame_num_value_allowed_flag = 0 // u(1)
>[ 000010110 ] pic_width_in_mbs_minus1 = 21(22) // ue(v)
>[ 000010010 ] pic_height_in_map_units_minus1 = 17(18) // ue(v)
>[ 0 ] frame_mbs_only_flag = 0			// u(1)
>[ 0 ] mb_adaptive_frame_field_flag = 0		// u(1)
>[ 1 ] direct_8x8_inference_flag = 1		// u(1)
>[ 0 ] frame_cropping_flag = 0			// u(1)
>[ 1 ] vui_parameters_present_flag = 1		// u(1)
>[ 1 ] aspect_ratio_info_present_flag = 1 	// u(1)
>[ 0000 0110 ] aspect_ratio_idc = 6 		// u(8)
>[ 1 ] overscan_info_present_flag = 1		// u(1)
>[ 1 ] overscan_appropriate_flag = 1		// u(1)
>[ 1 ] video_signal_type_present_flag = 1	// u(1)
>[ 101 ] video_format = 5				// u(3)
>[ 1 ] video_full_range_flag = 1			// u(1)
>[ 1 ] colour_description_present_flag = 1	// u(1)
>[ 0000 0101 ] colour_primaries = 5		// u(8)
>[ 0000 0101 ] transfer_characteristics = 5	// u(8)
>[ 0000 0101 ] matrix_coefficient = 5		// u(8)
>[ 1 ] chroma_loc_info_present_flag = 1		// u(1)
>[ 1 ] chroma_sample_loc_type_top_field = 0		// ue(v)
>[ 1 ] chroma_sample_loc_type_bottom_field = 0	// ue(v)
>[ 1 ] timing_info_present_flag = 1			// u(1)
>[ 0000 0000 0000 0000 0000 0000 1100 0000 ] num_units_in_tick = 192	// u(32)
>[ 0000 0001 0000 0000 0000 0000 0000 0000 ] time_scale = 16777216  // u(32)
>... 11 0000 0000 1100 1010 0001 0000 0000 0000
>
>Now the other program says the num_units_in_ticks is 1 and the time_scale is 
>50.  So 50 fields per second, which is obviously correct.  And my values make 
>no sense at all.  But from what I can see the spec is straight-forward--these 
>two values are simply u(32)'s, with no masking or other interpretation of any 
>kind.
>
>What am I missing?  Was there some kind of addendum to the spec since the 
>version I'm looking at?  Or some other text I'm missing?  
>
>Thanks for any help,
>Glenn
>
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