Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Control of information signal processing channel
Reexamination Certificate
1999-05-17
2002-06-11
Young, W. R. (Department: 2653)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Control of information signal processing channel
C369S030850, C369S053340, C369S047130
Reexamination Certificate
active
06404711
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, the present invention relates to an information outputting method, an information outputting apparatus adopting the method and a presentation medium for presenting the method. More particularly, the present invention relates to an information outputting apparatus capable of playing back a plurality of streams continuously with a high degree of reliability, an information outputting method adopted by the apparatus and a presentation medium for presenting the method.
In a digital television broadcast system such as a DVB (Digital Video Broadcasting) or a DTV (Digital Television), a transport stream of the MPEG2 systems (ISO/IEC 13818-1) is used in a multiplexing system. To be more specific, video and audio streams are multiplexed in a transport stream in transport-packet units each having a length of 188 bytes.
When transport packets of one or more television programs are extracted from a transport stream in which a plurality of television programs are multiplexed, the extracted transport packets appear at irregular intervals.
To put it in detail, in a stream transmitted through a satellite, transport packets of a plurality of channels are multiplexed as shown in FIG.
1
. In the example shown in the figure, transport packets of 4 channels, namely, channels A to D, are multiplexed. Assuming that transport packets of channel A are extracted from the stream, timings with which transport packets A
1
to A
5
are generated are irregular. That is to say, an interval between two adjacent transport packets A
i
and A
i+1
varies from time to time.
When such transport packets A
i
are recorded into a recording medium at the irregular intervals as they were extracted, however, the storage area of the recording medium is not utilized efficiently. Thus, transport packets A
i
need to be recorded by closing gaps between them.
If transport packets A
i
are thus recorded by closing gaps between them, however, it is necessary to adjust timings, with which transport packets A
i
are output in an operation to play back the transport packets A
i
from the recording medium, to the timings to which the packets have been transmitted. Otherwise, timing to supply the packets to an T-STD (Transport-System Target Decoder) prescribed by the MPEG2 standards will be different from the timing to encode the packets. As a result, it will be quite within the bounds of possibility that the T-STD fails. A conceivable solution to this problem is to also record a time stamp Tsi representing timing of generation of each transport packet in the transport packet at the same time as shown in FIG.
1
.
FIG. 2
is a block diagram showing a typical configuration of an apparatus for recording a transport stream by embracing such a principle. In a bitstream purser
2
, a program clock reference (PCR) is read out from the header of a transport packet of a transport stream received through a terminal
1
. The transport packet is supplied to a time-stamp adding circuit
3
while the PCR is supplied to a PLL (phase-locked loop) circuit
4
. The PLL circuit
4
generates a clock signal with a frequency of 27 MHz in synchronization with the PCR supplied thereto, outputting the clock signal to a time-stamp generating circuit
5
. The time-stamp generating circuit
5
counts the number of pulses of the clock signal and generates a time stamp (time_stamp_counter) corresponding to a count value to the time-stamp adding circuit
3
to output.
The time-stamp adding circuit
3
adds 3-byte TSP_extra_header to 187 bytes of the transport packet to generate a 190-byte block as shown in FIG.
3
. The 187 bytes are obtained by removing a sync byte at the beginning of the original 188-byte transport packet. As shown in
FIG. 4
, TSP_extra_header includes 21-byte time_stamp_counter. time_stamp_counter represents a planned arrival time of the first bit of the first byte of the transport packet at a smoothing buffer defined in the ISO/IEC13818-1.
It should be noted that the format shown in
FIG. 3
is a format for a transport-stream recording apparatus functioning as a digital VCR (Video Cassette Recorder) for use of consumer.
Data output by the time-stamp adding circuit
3
is supplied to a storage media unit
7
by way of a smoothing buffer
6
to be recorded therein.
A transport stream recorded in the storage media unit
7
in this way is played back by a playback apparatus having a configuration shown in FIG.
5
. As shown in the figure, a transport stream played back from the storage media unit
7
is supplied to a time-stamp separating circuit
21
for separating a transport packet and time_stamp_counter from the transport stream. The transport packet is supplied to an output control circuit
23
whereas time_stamp_counter is supplied to a comparator
22
and a timing generating circuit
24
.
In the timing generating circuit
24
, the number of clock pulses generated by a clock generating circuit
25
at a frequency of 27 MHz is counted by a counter with the value of first time_stamp_counter used as an initial value. A count value representing a time stamp is supplied to the comparator
22
. When the count value received from the timing generating circuit
24
becomes equal to the value of time_stamp_counter received from the time-stamp separating circuit
21
, the comparator
22
controls the output control circuit
23
to output the transport packet received from the time-stamp separating circuit
21
to a terminal
26
.
To be more specific, when the count value received from the timing generating circuit
24
is found equal to TS
1
by the comparator
22
, transport packet A
1
is output from the output control circuit
23
. By the same token, when the count value received from the timing generating circuit
24
becomes equal to TS
2
, transport packet A
2
is output from the output control circuit
23
. Thereafter, the same processing is repeated. Thus, transport packets A
i
are each output with the same timing as the encoding operation. As a result, it is possible to prevent the T-STD from failing.
When a stream of channel A and a stream of channel H are synthesized in editing work as shown in
FIG. 6
, however, continuity at a junction between the two streams is lost due to the fact that there is no relation between a time stamp TSn of the last transport packet A
n
of channel A and a time stamp TS
11
of the first transport stream packet H
1
of channel H.
As a result, when data obtained as a result of editing a plurality of streams in this way and recorded on storage media is played back, at the junction between the last transport packet A
n
of channel A and the first transport packet H
1
of channel H, a time stamp output by the timing generating circuit
24
does not correspond to a time stamp output by the time-stamp separating circuit
21
, raising a problem that it is no longer possible to correctly control the output control circuit
23
.
SUMMARY OF THE INVENTION
It is thus an object of the present invention addressing the problem described above to provide a capability of outputting transport packets correctly and continuously even from data obtained as a result of synthesizing a plurality of streams.
To achieve the above object, according to a first aspect of the present invention, there is provided an information outputting apparatus including; an extracting means for extracting a program clock reference and a transport packet from an input stream, a clock generating means for generating a clock signal synchronized with the program clock reference extracted by the extracting means, a time-stamp generating means for generating a time stamp in synchronization with the clock signal generated by the clock generating means, and an information generating means for generating information representing continuity of time stamps.
According to a second aspect of the present invention, there is provided an information outputting method characterized in that the method includes the steps of; an extracting step for extracting a program clock reference and a transport packet from an input
Frommer William S.
Sony Corporation
Young W. R.
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