Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output process timing
Reexamination Certificate
1999-06-09
2002-10-01
Gaffin, Jeffrey (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output process timing
C375S240000, C370S454000, C370S474000, C348S240200
Reexamination Certificate
active
06460097
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of The Invention
The present invention relates to a data stream output apparatus for sending out data coded in a specific style from a storage medium to a network More specifically, this invention concerns a data stream output apparatus for sending out data at a fixed rate—data which change in size with time.
2. Description of The Prior Art
Among the data which change in size with time is MPEG program stream data or video data
The MPEG video data including audio data is so designed that a group of pictures (GOP) (15 frames) of image data of three kinds—I, B and P pictures—makes up a unit of image data as illustrated in FIG.
3
(
b
) (
c
). Also, as shown in FIG.
3
(
d
), the video data of one GOP
303
is made up of a plurality of video packs Vp's. Furthermore, a required number of audio packs ap's are added to the plurality of video packs Vp's to constitute a system stream SS as shown in FIG.
3
(
e
).
At the pack header PH of each video pack in the system stream SS is written a system clock reference (SCR). This SCR serves as time base to control the timing for data to be handed over to an A/V separating means from a receive buffer on the terminal system side, which will be described below. Furthermore, each video pack is provided with a packet header KH. At each packet header KH are written a decoding time stamp (DTS) to serve as time base to control the decoding timing and a presentation time stamp (PTS) which is used as time base to regulate the display timing Each audio pack also has a pack header PH and a packet header KH.The packet header KH has PTS written in it. Furthermore, the top pack in each GOP is provided with a system header HS on which an identifier is written indicating the pack is at the top of the GOP. In practice, the DTS and PTS are written on packet headers as necessary depending on the types of I, B and P pictures, and not on all the packet headers.
In the MPEG program stream data thus configured, GOP's are not uniform in data size. For example, the data size is small where there are not much changes with time, while the data size is large where much changes with time take place.
FIG. 18
is a conceptual diagram showing an example which adopts a push-type send method. This push-type send method sends out the MPEG program stream data unilaterally without paying regard to the conditions at the terminal. The disk unit
10
a
in the video server system
100
stores the MPEG program stream data thus built. The video data including audio data which is DMA transferred from the disk unit
10
a
to the send buffer
10
b
is sent out to the terminal system
1500
via the network
300
. At the terminal system
1500
, the video data obtained that way is temporarily stored in the receive buffer
1510
and then is referred to a decoder
1520
at a specific time interval to be decoded. The decoded data is then displayed by a display means
1530
.
The above example presupposes that image data coded into MPEG program stream format has been stored in the disk unit
10
a
. Needless to say, image data which are not coded in MPEG program stream format and that are stored in the disk unit
10
a
may be encoded at the server system and sent out to the terminal.
FIG. 19
is a schematic illustration of a decoder
1520
provided in the terminal system
1500
. Each GOP as unit of video data (including audio data) which is temporarily stored in the receive buffer
1510
is inputted in an audio-video (A/V) separating means
1521
from the receive buffer
1510
with the timing based on the system clock reference (SCR) of each pack There, the video pack Vp is separated from the audio pack ap and is then decoded by a video decoding means
1522
according to the aforesaid DTS and outputted to the display means
1530
by a display coordination means
1523
according to PTS. The audio data ap is converted into audio signal by an audio decoding means
1524
according to PTS.
The push-type transfer system sends out variable encoded data such as MPEG program stream data that changes with time once the server side is ready to send out data even if not solicited from the terminal. Hitherto, it has been a usual practice to send out stored data compressed irrespective of the encoding rate or the reproduction rate at the terminal. And it has often happened that too much data reached the terminal beyond the decoding rate, that is, the data consuming rate. In that system, the timing or the interval at which data is transferred from the receive buffer
1510
to the A/V separating means
1521
is based on the aforesaid system clock reference. In addition, GOP's are different from each other in data size. Yet, the sending is always effected at a fixed rate determined on the basis of the capacity of the network So, it is often the case that data overflows the receive buffer
1510
before the decoding step at the terminal.
FIG. 15
is a time chart illustrating the shortcoming of the prior art in a conceptual manner. As described earlier (see FIG.
3
), one unit of MPEG data, that is, a group of pictures (GOP) is made up of 15 frames that consist of image data of three kinds—I, B and P pictures—which constitute an image unit. One GOP unit is equivalent to 0.5 second of decoding or reproduction.
Now, let it be supposed that as MPEG data shown in FIG.
15
(
a
) indicates in FIG.
15
(
b
), the MPEG data is sent out from a server on to a network where data can be transmitted at a fixed rate of
4
b
/second. In this connection, the figures—0.5 seconds—given on the upper side of FIG.
15
(
a
) indicate the decoding rate. Also, it should be presupposed that the terminal system
1500
shown in
FIG. 16
has a receive buffer
1510
with a capacity of
8
b
and that if data transmitted and stored reaches
4
b
in size, MPEG data will be reproduced, that is, decoded by the MPEG decoder
1520
. The outstanding data size or the remainder of data in the receive buffer
1510
is the total size of data inputted minus the total size of data decoded. The remainder changes with time as illustrated in FIG.
15
(
c
) and overflows the receive buffer
1510
in six seconds, turning to an error.
To illustrate,
4
b
of data ((
1
), (
2
)) are received by the receive buffer
1510
for the first one second, when decoding starts. In the next one second, an additional
4
b
of data (up to the first
1
b
of (
6
)) are received, while the first
4
b
((
1
) and (
2
)) are consumed. That leaves
4
b
of data in the receive buffer. In the next one second,
4
b
data (including the remaining
2
b
of (
6
)) are received, while
2
b
((
3
), (
4
)) are consumed. That leaves
6
b
in the receive buffer. That way, the receive buffer overflows in 6 seconds.
Attempts have been made to avoid that trouble with the prior art push-type transfer system which include increased capacity of the receive buffer, provision of a function to monitor the excess or shortage of data coming in at the terminal and to issue to the server a request for change in data sending rate. But those measures did not work with a network in which packets are sent out at a very high rate and in a very short cycle as exemplified by isochronous transfer under IEEE 1394. In such a network even if the terminal requested the server to change the data sending rate, the request failed to be processed in time, resulting in overflowing Another possible solution to the problem was to change the original data, the whole MPEG program stream to an MPEG transport stream suitable for the push-type transfer all over.
As a solution to the problem an arrangement as shown in FIG.
17
is proposed in the unexamined Japanese patent application laid open under No. 9-46691. Under this arrangement, a data coded by an encoder
1401
is controlled by a write controller
1403
and first stored in an encoded data storage memory (buffer)
1042
. Control information obtained from the encoder
1401
is also controlled by the write controller
1403
and is stored on a control information memory
1404
. The encoded data thus written in by
Harumoto Hideaki
Kobayashi Susumu
Morita Mitsuaki
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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