The MPEG-2 standard made many improvements to the MPEG-1 standard, including:
Â Support for interlaced video
Â Higher data rates and larger frame sizes, including internationally accepted standard
definition and high definition profiles
Â Two kinds of multiplexed system streams—Transport Streams (TS) for unreliable
network transmission such as broadcast digital television, and Program Streams (PS)
for local, reliable media access (such as DVD playback)
MPEG-2 categorizes video standards into MPEG-2 Profiles and MPEG-2 Levels. Profiles
define the type of MPEG encoding supported (I-, P-, and B-frames) and the color
sampling method used (4:2:0 or 4:2:2 Y´C
). For example, the MPEG-2 Simple Profile
(SP) supports only I and P progressive frames using 4:2:0 color sampling, whereas the
High Profile (HP) supports I, P, and B interlaced frames with 4:2:2 color sampling.
Levels define the resolution, frame rate, and bit rate of MPEG-2 video. For example,
MPEG-2 Low Level (LL) is limited to MPEG-1 resolution, whereas High Level (HL)
supports 1920 x 1080 HD video.
MPEG-2 formats are often described as a combination of Profiles and Levels. For
example, DVD video uses Main Profile at Main Level (MP @ ML), which defines SD NTSC
and PAL video at a maximum bit rate of 15 (though DVD limits this to 9.8 Mbps).
MPEG-2 supports the same audio layers as MPEG-1 but also includes support for
multichannel audio. MPEG-2 Part 7 also supports a more efficient audio compression
algorithm called Advanced Audio Coding, or AAC.
MPEG-2 elementary stream files often have extensions such as .m2v and .m2a, for video
and audio, respectively.