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1078 Part XIII Appendixes
MPEG-1
MPEG-1 is the earliest format specification in the family of MPEG formats. Because of its
low bit rate, MPEG-1 has been popular for online distribution and in formats such as Video
CD (VCD). DVDs can also store MPEG-1 video, though MPEG-2 is more commonly used.
Although the MPEG-1 standard actually allows high resolutions, almost all applications use
NTSC- or PAL-compatible image dimensions at quarter resolution or lower.
Common MPEG-1 formats include 320 x 240, 352 x 240 at 29.97 fps (NTSC), and
352 x 288 at 25 fps (PAL). Maximum data rates are often limited to around 1.5 Mbps.
MPEG-1 only supports progressive-scan video.
MPEG-1 supports three layers of audio compression, called MPEG-1 Layers 1, 2, and 3.
MPEG-1 Layer 2 audio is used in some formats such as HDV and DVD, but MPEG-1 Layer
3 (also known as MP3) is by far the most ubiquitous. In fact, MP3 audio compression
has become so popular that it is usually used independently of video.
MPEG-1 elementary stream files often have extensions such as .m1v and .m1a, for video
and audio, respectively.
MPEG-2
The MPEG-2 standard made many improvements to the MPEG-1 standard, including:
 Support for interlaced video
 Higher data rates and larger frame sizes, including internationally accepted standard
definition and high definition profiles
 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
B
C
R
). 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).