Moving Pictures
• MPEG, Motion Picture Experts Group
• MPEG is a set of standards designed to support
”Coding of Moving Pictures and Associated Audio –
for digital storage media at up to 1.5 Mbits/s”.
• MPEG-1 (Nov 1992) was designed to permit full
motion video recordings on CD players originally
designed for stereo audio playback.
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• MPEG-2 or ITU-T-recommendation H.262, Generic
Coding of Moving Pictures and Associated Audio
(Nov 1994), addressed greater input-output format
flexibility, data rates, and system considerations such
as transport and synchronization, topics neglected in
MPEG-1.
• MPEG-2 supports variations of Digital TV.
• The following section describes the basic theory of
operation of the simplest version of MPEG-2:
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• MPEG compresses a sequence of moving images by
taking advantage of the high correlation that exists
between successive pictures of a moving picture.
• MPEG constructs three types of pictures: Intra
pictures (I-pictures), Predicted pictures (P-pictures),
and Bi-directional Prediction pictures (B-pictures).
• In MPEG, every M-th picture in a sequence can be
fully compressed using a standard JPEG algorithm;
these are the I-pictures.
• The process then compares successive I-pictures
and identifies portions of the image that have moved.
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• The image sections that didn’t move are carried
forward in time to intermediate pictures by the
decoder memory.
• The process then selects a subset of intermediate
pictures, then predicts (via linear interpolation
between I-pictures) and corrects the location of the
image sections that were found to have moved.
• These predicted and corrected images are the Ppictures.
• The pictures between the I- and P-pictures are the Bpictures that incorporate the stationary image
sections uncovered by moving sections.
• The I-pictures are compressed as if they were JPEG
images.
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• MPEG-4 is a patented collection of methods defining
compression of audio and visual (AV) digital data. It
was introduced in late 1998.
• Uses of MPEG-4 include compression of AV data for
web (streaming media) and CD distribution, voice
(telephone, videophone) and broadcast television
applications.
• MPEG-4 absorbs many of the features of MPEG-1
and MPEG-2 and other related standards, adding
new features such as (extended) VRML support for
3D rendering, object-oriented composite files
(including audio, video and VRML objects), support
for externally-specified Digital Rights Management
and various types of interactivity. AAC (Advanced
Audio Codec) was standardized as an adjunct to
MPEG-2 (as Part 7) before MPEG-4 was issued.
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• MPEG-4 is still a developing standard and is divided
into a number of parts. Companies promoting MPEG4 compatibility do not always clearly state which
"part" level compatibility they are referring to. The key
parts to be aware of are MPEG-4 part 2 (including
Advanced Simple Profile, used by codecs such as
DivX, Xvid and Nero Digital) and MPEG-4 part 10
(MPEG-4 AVC/H.264 or Advanced Video Coding,
used by the x264 codec, by Nero Digital AVC, and by
next-gen video medium formats like Blu-ray Disc).
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• Most of the features included in MPEG-4 are left to
individual developers to decide whether to implement
them. This means that there are probably no
complete implementations of the entire MPEG-4 set
of standards. To deal with this, the standard includes
the concept of "profiles" and "levels", allowing a
specific set of capabilities to be defined in a manner
appropriate for a subset of applications.
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• Initially, MPEG-4 was aimed primarily at low bit-rate
video communications; however, its scope was later
expanded to be much more of a multimedia coding
standard. MPEG-4 is efficient across a variety of bitrates ranging from a few kilobits per second to tens of
megabits per second. MPEG-4 provides the following
functionalities:
– Improved coding efficiency
– Ability to encode mixed media data (video, audio, speech)
– Error resilience to enable robust transmission
– Ability to interact with the audio-visual scene generated at
the receiver
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• The H.264/MPEG-4 AVC standard includes for
example the following sets of capabilities, which are
referred to as profiles, targeting specific classes of
applications:
• Constrained Baseline Profile (CBP)
• Primarily for low-cost applications this profile is used
widely in videoconferencing and mobile applications.
It corresponds to the subset of features that are in
common between the Baseline, Main, and High
Profiles described below.
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• Baseline Profile (BP)
• Primarily for low-cost applications that requires
additional error robustness, while this profile is used
rarely in videoconferencing and mobile applications, it
does add additional error resilience tools to the
Constrained Baseline Profile. The importance of this
profile is fading after the Constrained Baseline Profile
has been defined.
• Main Profile (MP)
• Originally intended as the mainstream consumer
profile for broadcast and storage applications, the
importance of this profile faded when the High profile
was developed for those applications.
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• Extended Profile (XP)
• Intended as the streaming video profile, this profile
has relatively high compression capability and some
extra tricks for robustness to data losses and server
stream switching.
• High Profile (HiP)
• The primary profile for broadcast and disc storage
applications, particularly for high-definition television
applications (this is the profile adopted into HD DVD
and Blu-ray Disc, for example).
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• High 10 Profile (Hi10P)
• Going beyond today's mainstream consumer product
capabilities, this profile builds on top of the High
Profile, adding support for up to 10 bits per sample of
decoded picture precision.
• High 4:2:2 Profile (Hi422P)
• Primarily targeting professional applications that use
interlaced video, this profile builds on top of the High
10 Profile, adding support for the 4:2:2 chroma
subsampling format while using up to 10 bits per
sample of decoded picture precision.
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• High 4:4:4 Predictive Profile (Hi444PP)
• This profile builds on top of the High 4:2:2 Profile,
supporting up to 4:4:4 chroma sampling, up to 14 bits
per sample, and additionally supporting efficient
lossless region coding and the coding of each picture
as three separate color planes.
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