TABLE OF CONTENTS MPEG-2 video syntax for the main profile is a superset of the MPEG-1 video syntax. This nonscalable profile is aimed at higher bit rates than MPEG-1 and is able to handle interlaced video formats. [1] In the discussions in this chapter the data element ranges are restricted to main profile at main level (MP@ML). Higher MPEG-2 levels allow a broader range of values, but have no other effect on the syntax.
MPEG-2 uses exactly the same video start codes as MPEG-1 in its video sequences (see Table 8.1). If the sequence_extension (signaled by the extension_start_code) occurs immediately after the sequence header, the sequence is an MPEG-2 video sequence. This sequence extension is not allowed in MPEG-1 and, therefore, is a means by which a decoder can differentiate between MPEG-1 and MPEG-2 video bitstreams. MPEG-2 also requires a picture extension immediately after the picture header and defines a number of optional sequence and picture extensions.
The parameter ranges allowed in MPEG-2 sometimes exceed the precision defined in the MPEG-1 syntax. Parameter range expansion is usually accomplished in MPEG-2 by defining the MPEG-1 data element to be the low-order bits and using an extension to communicate the high-order bits.
[1]MPEG-2 system syntax has already been briefly described in Chapter 9.
