Contents Page

səhifə	6/35
tarix	25.06.2016
ölçüsü	2.59 Mb.

1 2 3 4 5 6 7 8 9 ... 35

6.2 Video bitstream syntax

6.2.1 Start codes

Start codes are specific bit patterns that do not otherwise occur in the video stream.

Each start code consists of a start code prefix followed by a start code value. The start code prefix is a string of twenty three bits with the value zero followed by a single bit with the value one. The start code prefix is thus the bit string ‘0000 0000 0000 0000 0000 0001’.

The start code value is an eight bit integer which identifies the type of start code. Most types of start code have just one start code value. However slice_start_code is represented by many start code values, in this case the start code value is the slice_vertical_position for the slice.

All start codes shall be byte aligned. This shall be achieved by inserting bits with the value zero before the start code prefix such that the first bit of the start code prefix is the first (most significant) bit of a byte.

Table 6-1 defines the slice start code values for the start codes used in the video bitstream.

Table 6-1 — Start code values

name

start code value

(hexadecimal)

picture_start_code

00

slice_start_code

01 through AF

reserved

B0

system start codes (see note)

B9 through FF

NOTE - system start codes are defined in Part 1 of this specification

The use of the start codes is defined in the following syntax description with the exception of the sequence_error_code. The sequence_error_code has been allocated for use by a media interface to indicate where uncorrectable errors have been detected.

6.2.2 Video Sequence

video_sequence() {	No. of bits	Mnemonic
next_start_code()
sequence_extension()
}
} while ( nextbits() != sequence_end_code )
} else {
/* ISO/IEC 11172-2 */
}

6.2.2.1 Sequence header

sequence_header() {	No. of bits	Mnemonic
sequence_header_code	32	bslbf
non_intra_quantiser_matrix[64]	8*64	uimsbf
}

6.2.2.2 Extension and user data

extension_and_user_data( i ) {	No. of bits	Mnemonic
while ( ( nextbits()== extension_start_code ) \|\|
}

6.2.2.2.1 Extension data

extension_data( i ) {	No. of bits	Mnemonic
while ( nextbits()== extension_start_code ) {
}

6.2.2.2.2 User data

user_data() {	No. of bits	Mnemonic
user_data_start_code	32	bslbf
}

6.2.2.3 Sequence extension

sequence_extension() {	No. of bits	Mnemonic
extension_start_code	32	bslbf
}

6.2.2.4 Sequence display extension

sequence_display_extension() {	No. of bits	Mnemonic
extension_start_code_identifier	4	uimsbf
}

6.2.2.5 Sequence scalable extension

sequence_scalable_extension() {	No. of bits	Mnemonic
extension_start_code_identifier	4	uimsbf
}

6.2.2.6 Group of pictures header

group_of_pictures_header() {	No. of bits	Mnemonic
group_start_code	32	bslbf
}

6.2.3 Picture header

picture_header() {	No. of bits	Mnemonic
picture_start_code	32	bslbf
}

6.2.3.1 Picture coding extension

picture_coding_extension() {	No . of bits	Mnemonic
extension_start_code	32	bslbf
chroma_420_type	1	uimsbf
}

6.2.3.2 Quant matrix extension

quant_matrix_extension() {	No. of bits	Mnemonic
extension_start_code_identifier	4	uimsbf
}

6.2.3.3 Picture display extension

picture_display_extension() {	No. of bits	Mnemonic
extension_start_code_identifier	4	uimsbf
}

6.2.3.4 Picture temporal scalable extension

picture_temporal_scalable_extension() {	No. of bits	Mnemonic
extension_start_code_identifier	4	uimsbf
}

6.2.3.5 Picture spatial scalable extension

picture_spatial_scalable_extension() {	No. of bits	Mnemonic
extension_start_code_identifier	4	uimsbf
}

6.2.3.6 Copyright extension

copyright_extension() {	No. of bits	Mnemonic
extension_start_code_identifier	4	uimsbf
}

6.2.3.7 Picture data

picture_data() {	No. of bits	Mnemonic
do {
}

6.2.4 Slice

slice() {	No. of bits	Mnemonic
slice_start_code	32	bslbf
macroblock()
}

6.2.5 Macroblock

macroblock() {	No. of bits	Mnemonic
while ( nextbits() == ‘0000 0001 000’ )
}

6.2.5.1 Macroblock modes

macroblock_modes() {	No. of bits	Mnemonic
macroblock_type	1-9	vlclbf
}

6.2.5.2 Motion vectors

motion_vectors ( s ) {	No. of bits	Mnemonic
if ( motion_vector_count == 1 ) {
}

6.2.5.2.1 Motion vector

motion_vector ( r, s ) {	No. of bits	Mnemonic
motion_code[r][s][0]	1-11	vlclbf
}

6.2.5.3 Coded block pattern

coded_block_pattern () {	No. of bits	Mnemonic
coded_block_pattern_420	3-9	vlclbf
}

6.2.6 Block

The detailed syntax for the terms “First DCT coefficient”, “Subsequent DCT coefficient” and “End of Block” is fully described in 7.2.

This clause does not adequately document the block layer syntax when data partitioning is used. See 7.10.

block( i ) {	No. of bits	Mnemonic
if ( pattern_code[i] ) {
}

1 2 3 4 5 6 7 8 9 ... 35