Pulse or digital communications – Bandwidth reduction or expansion
Reexamination Certificate
1998-07-21
2001-11-06
Kelley, Chris (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
C382S234000, C382S238000
Reexamination Certificate
active
06314138
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of switching from a first coded video sequence to a second one, said video sequences having been encoded by different video encoders using regulation buffers, and to a corresponding switching device. This invention may be used for instance in MPEG1 or MPEG2 encoding/decoding systems.
Encoding systems such as those according to the MPEG
2
standard produce data at variable rates (encoded pictures have variable sizes in bits) and require an output data buffer in order to feed the (constant bitrate) transmission channel. Similarly the corresponding decoders require an input data buffer to enable them to use data from said channel at the required variable rates. The transmitted encoded pictures will therefore not spend the same time in the decoder buffer. As a consequence, when switching from a first video sequence to a second one, the respective decoder buffer delays at the transition (or switching point) are not equal.
It is known indeed that, thanks to the abstract model of decoding VBV (
V
ideo
B
uffer
V
erifier) defined in the MPEG standard, it is possible to verify that an MPEG bitstream is decodable with reasonable buffering and delay requirements (expressed in the sequence header, in the fields “bitrate” and “buffer size”). This model of VBV is that of a receiving buffer for the coded bitstream and an associated instantaneous decoder so that all the data for a picture are instantaneously removed from said receiving buffer. Within the framework of this model, constraints on the bitstream (by way of the buffer occupancy) have been defined so that decoding can occur without buffer underflow or overflow. If said first and second sequences to be switched have been separately encoded, such a risk of overflow or underflow for the decoder buffer however exists.
In order to prevent such a risk, the switching operation may be performed in the decompressed domain where all the decoded pictures are again described with the same number of bits and last a same duration. Said pictures are then sent to a conventional mixer for switching, and recoded before transmission. Such a solution, described for example in the international patent application WO 97/08898, is however rather complex. Moreover, a decoding step followed by a re-encoding one damages the picture quality.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to propose another switching method that overcomes these drawbacks.
To this end the invention relates to a switching method such as described in the preamble of the description and wherein the switching step is preceded by a transcoding step of each of said coded sequences, provided for shifting the temporal position of the switching point. The invention also relates to a corresponding device.
The basic idea of this solution is to transcode the input encoded streams such that they have at the switching point, now chosen a posterior, the same decoder buffer characteristics, and particularly buffer delays that now are equal.
REFERENCES:
patent: 4706260 (1987-11-01), Fedele et al.
patent: 5455829 (1995-10-01), Klingberg
patent: 5513181 (1996-04-01), Bresalier et al.
patent: 5537440 (1996-07-01), Eyuboglu et al.
patent: 5544266 (1996-08-01), Koppelmans et al.
patent: 5550589 (1996-08-01), Shiojiri et al.
patent: 5583562 (1996-12-01), Birch et al.
patent: 5606371 (1997-02-01), Klein Gunnewiek et al.
patent: 5608779 (1997-03-01), Lev et al.
patent: 5621820 (1997-04-01), Rynderman et al.
patent: 5623308 (1997-04-01), Civanlar et al.
patent: 5764298 (1998-06-01), Morrison
patent: 5835498 (1998-11-01), Kim et al.
patent: 0690392 A (1996-03-01), None
patent: WO 9529561 A (1995-11-01), None
patent: WO 9625823 A (1996-08-01), None
patent: WO9708898 (1997-03-01), None
patent: WO 9708898 A (1997-06-01), None
“Splicing MPEG Video Streams in the Compressed Domain”, by Susie J. Wee et al, IEEE Workshop on Multimedia Signal Processing, Jun. 23, 1997, pp. 225-230, XP000957700.
An Shawn S.
Gathman Laurie E.
Kelley Chris
U.S. Philips Corporation
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