84 How does MPEG achieve compression? Misc.:
Description
This article is from the MPEG FAQ, by Frank Gadegast phade@cs.tu-berlin.de with numerous contributions by others.
84 How does MPEG achieve compression? Misc.:
copyright_id extension can identify whether a sequence or subset of
frames within the sequence is copyrighted, and provides a unique 64-bit
copyright_id_number registered with the ISO/IEC.
Syntax can now signal frame sizes as large as 16383 x 16383. Since
MPEG-1 employed a meager 12-bits to describe horizontal_size and
vertical_size , the range was limited to 4095x4095. However, MPEGs
Levels prescribe important interoperability points for practical
decoders. Constrained Parameters MPEG-1 and MPEG-2 Low Level limit the
sample rate to 352x240x30 Hz. MPEG-2s Main Level defines the limit at
720x480x30 Hz. Of course, this is simply the restriction of the dot
product of horizontal_size, vertical_size, and frame_rate. The Level
also places separate restrictions on each of the these three
variables.
Reflecting the more television oriented manner of MPEG-2, the optional
sequence_display_extension() header can specify the chromaticy of the
source video signal as it was prior to representation by MPEG syntax.
This information includes: whether the original video_format was
composite or component, the opto-electronic transfer_characteristics,
and RGB->YCbCr matrix_coefficients. The picture_display_extension()
provides more localized source composite video characteristics on a
frame by frame basis (not field-by-field), with the syntax elements:
field_sequence, sub_carrier_phase, and burst_amplitude. This
information can be used by the displays post-processing stage to
reproduce a more refined display sequence.
Optional pan & scan syntax was introduced which tells a decoder on a
frame-by-frame basis how to, for example, window a 4:3 image within the
wider 16:9 aspect ratio of the coded frame. The vertical pan offset
can be specified to within 1/16th pixel accuracy.
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