Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-03-25
2003-05-20
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06567471
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an editing system, method and apparatus for editing images and, more particularly, an editing system, method and apparatus for seamlessly splicing a plurality of bit streams of video data.
2. Related Art
Recording/reproducing systems have recently been introduced which record/reproduce high quality audio/video data utilizing compression schemes. High quality recording/reproducing systems compression-encode/decode the audio/video data utilizing the MPEG (Moving Picture Experts Group) standard. One example of such a system is the DVD (Digital Versatile Disk or Digital Video Disk), which provides a powerful means by which unprecedented quantities of high quality audio/video are compressed on an optical disk.
FIG. 1
illustrates the general recording/reproducing system. The video encoder
111
of the encoding-side apparatus
110
encodes input video data D
v
in accordance with the MPEG standard to thereby produce a video elementary stream (video ES). The packetizer
112
packetizes the video elementary stream into a video packetized elementary stream (video PES) comprising access units; each access unit representing a picture in a group of pictures making up a portion of the video program. The audio encoder
113
of the encoding-side apparatus encodes input audio data D
A
to thereby produce an audio elementary stream (audio ES) The packetizer
114
formats the audio elementary stream into an audio packetized elementary stream (audio PES) comprising access PATENT units; each access unit represent decodable segment of an audio bit stream. The transport stream multiplexer
115
multiplexes the audio and video packetized elementary streams to thereby produce a transport stream packet. A Video Buffer Verifier (VBV) buffer (not shown) stores/retrieves the multiplexed streams at a variable target rate which is controlled in accordance with the number of bits to be encoded and the capacity of the VBV buffer. An illustration of the Video Buffer Verifier is provided with reference to FIG.
2
.
The decoding-side apparatus
120
of
FIG. 1
stores in a decoding-side Video Buffer Verifier (VBV) buffer (not shown) the received transport stream which is transmitted via the transmission medium
116
. The transport stream demultiplexer
121
demultiplexes the received transport stream fetched from the decoding buffer at a timing determined by a decoding time stamp (DTS) to thereby reproduce the video packetized elementary stream (video PES) and the audio packetized elementary stream (audio PES). The video packetized elementary stream is depacketized by depacketizer
122
and decoded by video decoder
123
thereby reproducing the video data D
v
. The audio packetized elementary stream is depacketized by depacketizer
124
and decoded by audio decoder
125
thereby reproducing the audio data D
A
. For DVD applications, the transport stream multiplexer
115
and the transport stream demultiplexer
121
are respectively replaced with a program stream multiplexer and demultiplexer which DVD format/unformat the encoded bit streams.
In the recording/reproducing system of
FIG. 1
, it is desirable to seamlessly splice a plurality of bit streams by concentrating at the transport level two or more different elementary streams representing the merger of different video programs. In digital broadcasting, for example, editors at a broadcasting station splice a plurality of bit streams from different video sources such as, for example, live video feeds received from local stations for generating a spliced broadcast video program. In DVD applications, the director splices movie scenes to be recorded on the DVD optical disk. In another DVD application, the DVD decoder splices multiple bit streams reproduced from the DVD optical disk in response to user-entered actions which is particularly useful for generating alternate scenes for interactive movies and video games.
There are, however, unforeseen difficulties to splicing a plurality of bit streams using the MPEG compression standard. In order to illuminate the problem, a closer look at MPEG is warranted. In summary, the MPEG standard implements a compression process which includes motion-compensated predictive coding in conjunction with adaptive Discrete Cosine Transform (DCT) quantization. The motion-compensated predictive coding predicts motion in each image frame/field using both unidirectional and bidirectional motion prediction. The DCT quantization adaptively compresses each frame/field in accordance with the motion-compensated prediction. The term “frames” hereinafter refers to-pictures in general including frames as well as fields.
As illustrated in FIG.
3
(
a
), motion-compensated prediction of the MPEG compression standard classifies the frames into one of three types: intracoded-frames (I-frames), predictively coded frames (P-frames) and bi-directionally coded frames (B-frames). MPEG establishes the I-frames as the reference by which the B- and P-frames are encoded and, thus, preserves the I-frames as complete frames. The I-frames are considered “intra-coded” since they proceed as complete frames, having bypassed the motion-compensated prediction, to the DCT quantization whereupon each I-frame is compression encoded with reference only to itself. P-frames, which rely on forward temporal prediction, are coded using the previous I- or P-frame. B-frames are coded using bi-directional (forward and/or backward) motion compensated predictive encoding using the two adjacent I- and/or P-frames. B- and P-frames are considered “inter-coded” since they are motion-prediction encoded with reference to other frames.
FIG. 7
illustrates an example of the direction of prediction for each I, B and P-frame in a group of pictures (GOP) as indicated by the arrows in the figure.
In accordance with the MPEG standard, frames are arranged-in ordered groups of pictures (GOP), each group of pictures comprising a closed set of I-, B- and P-frames which are encoded with reference to only those frames within that group. FIG.
3
(
a
) illustrates the natural presentation order (
1
to
15
) of the GOP in which the pictures are naturally presented to the viewer. Since the B- and P-frames within the GOP are encoded with reference to other frames, the MPEG standard dictates that the natural presentation order shown in FIG.
3
(
a
) be rearranged into the decoding order shown in FIG.
3
(
b
) in which the frames are to be decoded and transmitted in the coded order shown in FIG.
3
(
c
). With this arrangement, the frames necessary for decoding other frames are-first.decoded to provide the basis upon which the following inter-coded frames are decoded. For example, an I-frame which forms the reference by which the following frames in the GOP are motion-compensation predicted is positioned first in the decoding order. Once decoded, the pictures are rearranged in their natural presentation order for display to the viewer.
Motion-compensated predictive coding divides each I-, B- and P-frame into 8×8 pel macroblocks. The motion vectors for a present-frame are motion-compensation predicted with reference to the motion vectors of another frame which is selected in accordance with the direction of prediction of the type of frame (e.g., I-, B- or P-frame). For example, P-frame macroblocks are motion-predicted with reference to the macroblocks in a previous I or P-frame; B-frame macroblocks are motion-predicted with reference to the previous/successive I- and/or P-frames. The I-frames, which are not inter-coded, bypass motion compensation and are directly DCT quantized.
The process for motion-predicting a current picture in a GOP is illustrated in FIGS.
4
(
a
)-(
e
). The GOP are input in the natural presentation order shown in FIG.
4
(
a
), rearranged in accordance with the decoding order shown in FIG.
4
(
b
), motion-predicted utilizing two frame memories (FM
1
, FM
2
) as shown in FIGS.
4
(
c
) and (
d
) and output in the form of the encoding stream (ES) shown in FIG.
4
(
e
). For example, t
Bugg George A
Frommer & Lawrence & Haug LLP
Kelley Chris
Smid Dennis M.
Sony Corporation
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