Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-02-28
2004-01-27
Philippe, Gims (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C386S349000, C386S349000, C382S232000, C348S423100, C370S342000
Reexamination Certificate
active
06683911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a stream editing apparatus designed to edit streams consisting of a combination of video and audio data codes, and more particularly to a stream editing apparatus designed to connect two streams, in real time, to produce a single stream without deterioration in image quality.
2. Background Art
In the MPEG format that is a typical one of video and audio code compression coding techniques, compression coding of moving pictures is achieved by decreasing the amount of data using the discrete cosine transform (DTC) and predictive coding.
FIG. 11
shows an encoder designed to perform such a coding operation.
The encoder includes a subtractor
41
, a DCT circuit
42
, a quantizer
43
, a variable length coding circuit
49
, a buffer
50
, an inverse quantizer
44
, an inverse DCT circuit
45
, an adder
46
, an image memory
47
, and a motion vector detector
48
.
When the interframe predictive coding is performed, the motion vector detector
48
compares input image data with image data stored in the image memory
47
to calculate a motion vector (MV) and outputs it to the image memory
47
and the variable length coding circuit
49
.
The subtractor
41
reads motion-compensated image data out of the image memory
47
and outputs a difference between the input image data and the image data read from the image memory
47
to the DCT circuit
42
. The DCT circuit
42
performs the discrete cosine transform on the difference data inputted from the subtractor
41
and outputs DCT coefficients thereof to the quantizer
43
to inform the variable length coding circuit
49
of the type of the DCT.
The quantizer
43
quantizes the DCT coefficients at quantization steps specified by quantizer matrix (Quant) from the buffer
50
and outputs results of the quantization and the quantizer matrix (Quant) to the variable length coding circuit
49
. The results of the quantization are also outputted to the inverse quantization circuit
44
.
The variable length coding circuit
49
codes a motion vector (MV) calculated by the motion vector detector
48
, the type of DCT, the quantizer matrix (Quant), and the output of the quantizer
43
. These coded data are stored in the buffer
50
temporarily and then outputted in the form of a stream.
The output of the quantizer
43
is also inverse-quantized by the inverse quantizer
44
and then subjected to the inverse DCT in the inverse DCT circuit
45
. The output of the inverse DCT circuit
45
is added by the adder
46
to the image data read out of the image memory
47
to reproduce the input image data which is, in turn, stored in the image memory
47
again for use in the subtraction operation on a subsequent input image data.
When the intraframe coding is performed which does not use the interframe prediction, only the DCT is performed without reading the image data out of the image memory
47
.
When the interframe prediction is used, the forward interframe predictive coding using a previous image stored in the image memory
47
and the backward interframe predictive coding using a future image stored in the image memory
47
may also be performed.
In the MPEG format, each input frame is coded into one of three pictures: an I-picture containing only intra-macroblocks, a P-picture containing intra- and forward interframe predictive coded microblocks, and a B-picture containing intra-, forward interframe predictive coded, and backward interframe predictive coded macroblocks.
FIGS.
10
(
a
) to
10
(
d
) show a sequence of processes which adds audio data to video data coded in the above described manner to produce a data stream in a format suitable for a storage medium.
Moving pictures are placed in an frame order different from that when they are inputted and coded into I-, P-, and B-pictures to produce a video elementary stream (ES). The audio data is compressed at an interval of, for example, 24 ms. to produce an audio ES. These ESs are each divided into suitable units and packetized together with headers. To each header, a PTS (Presentation Time Stamp) is added which indicates the time the packtized data is to be reproduced.
The thus formed video and audio packets are multiplexed as a pack along with a header to form a stream
FIG. 9
shows typical packed streams. The streams are recorded in a storage medium such as a DVD. The playback is achieved by reading the streams out of the storage medium and decoding and reproducing each packet at the time specified by the PTS.
Usually, production of streams of desired contents from a plurality of streams recorded in a storage medium is accomplished by reading the streams out of the storage medium and rearranging them. For instance, when it is required to split a stream A into two sections and replace a stream B between them to produce a stream C, the first section of the stream A is decoded and then encoded again to prepare a leading portion of the stream C, after which the second section of the stream A is decoded and then encoded again to produce a trailing portion of the stream C. Such stream editing, however, encounters a drawback in that the re-encoding operation degrades the quality of edited image.
Editing techniques for coupling the streams directly to each other are also proposed, but they are subjected to restriction that the streams should be coupled at an I-picture of video data.
In the MPEG format, video data is grouped in units of a GOP (Group of Pictures) consisting of one I-picture and a plurality of P- and B-pictures. Each GOP usually contains fifteen (15) pictures (0.5 sec.). If a streams is divided at one of the P-pictures or the B-pictures, it is difficult to reproduce a frame image in units of a picture, thus leading to a problem that the image continues to be distorted until a subsequent I-picture appears.
The above editing is usually performed in an off-line operation and thus consumes much time.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a stream editing system designed to connect two streams, in real time, to produce a single stream without deterioration in signal quality such as image quality.
According to one aspect of the invention, there is provided a stream editing apparatus which is designed to switch one of two input streams used in an editing operation to the other at an edit point set in each of the streams. The system comprises: (a) a first decoder decoding a first stream; (b) a second decoder decoding a second stream; (c) an encoder re-encoding at least one of the first and second streams decoded by the first and second decoders; and (d) a controller controlling editing of the first and second streams to produce a third stream made up of a combination of a leading segment of the first stream preceding the edit point set in the first stream and a trailing segment of the second stream following the edit point set in the second stream, the controller, in producing the third stream, combining a portion of at least one of the leading and trailing segments of the first and second streams which is decoded and re-encoded by a corresponding one of the first and second decoders and the encoder and which is defined to have a given length from the edit point set in the one of the first and second streams with other portions of the leading and trailing segments of the first and second streams before decoded and re-encoded by the first and second decoders and the re-encoder.
In the preferred mode of the invention, each of the first and second streams is made up of a plurality of groups of pictures (GOP). The controller defines the length of the portion which is decoded and re-encoded and which is to be combined in the third stream from edit point to a leading portion of one of the GOPs in which the edit point is set.
A header generator may further be provided which generates a series of headers for the third stream.
The encoder may re-encod
Connely Bove Lodge & Hutz LLP
Matsushita Electric - Industrial Co., Ltd.
Philippe Gims
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