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Claims  |
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We claim:
1. A method of transmitting a video bitstream from a transmitter over a
facility to a receiver, the video bitstream including a plurality of high
priority segments and associated low priority segments, said method
comprising the steps of
at the transmitter,
first transmitting a high priority partition, including the high priority
segments, of the video bitstream over the facility using a first packet
delivery mechanism having a first probability of success;
subsequently transmitting, after the completion of transmission of the high
priority partition, a low priority partition, including the low priority
segments, of the video bitstream over the facility in real time using
second packet delivery mechanism having a second probability of success
which is substantially lower than that of the first delivery mechanism;
and
at the receiver,
receiving and storing the high priority partition;
receiving the low priority partition; and
interleaving each high priority segment, obtained from storage, in real
time with the associated received low priority segment to create an
interleaved video bitstream.
2. A method of transmitting a video bitstream from a transmitter over a
facility to a receiver, the video bitstream including a plurality of high
priority segments and associated low priority segments, said method
comprising the steps of
at the transmitter,
first transmitting high priority information, representative of the high
priority segments, over the facility using a first packet delivery
mechanism having a first probability of success;
subsequently transmitting, after the completion of transmission of the high
priority information, a low priority partition, including the low priority
segments, of the video bitstream over the facility in real time using a
second packet delivery mechanism having a second probability of success
which is substantially lower than that of the first delivery mechanism;
and
at the receiver,
receiving the high priority information and using it to generate the high
priority segments;
receiving the low priority partition; and
interleaving each generated high priority segment in real time with the
associated received low priority segment to create an interleaved video
bitstream.
3. The method of claim 2 wherein the first packet delivery mechanism
provides reliable error-free delivery of packets over the facility and
said second packet delivery mechanism uses a less-reliable delivery
mechanism.
4. The method of claim 2 including the steps of
at the transmitter,
receiving a video bitstream having high priority segments interleaved with
associated low priority segments; and
partitioning the video bitstream into a high priority partition and a low
priority partition prior to said first transmitting step.
5. The method of claim 4 further including the steps of
at the transmitter,
receiving a video bitstream having high priority segments interleaved with
associated low priority segments;
storing the video bitstream;
generating a table identifying the association between high priority
segments and low priority segments in the video bitstream; and
creating the high priority partition using the table to access the high
priority segments from the stored video bitstream prior to said first
transmitting step.
6. The method of claim 5 wherein the table identifies the storage location
of the high priority segments.
7. The method of claim 6 wherein a time stamp is used to identify the
association between the high priority segments and the low priority
segments.
8. The method of claim 6 wherein a frame identifier is used to identify the
association between the high priority segments and the low priority
segments.
9. The method of claim 8 further including the step of
at the transmitter,
receiving a video bitstream having a high priority partition, including the
high priority segments, and a low priority partition, including the low
priority segments, prior to said first transmitting step.
10. The method of claim 2 further including the steps of
at the receiver,
requesting a delivery of a bitstream of an identified video segment; and
at the transmitter,
receiving the video segment request and in response thereto accessing the
bitstream for the identified video segment prior to the transmitting step.
11. The method of claim 2 further including the steps of
at the receiver,
sending a control command request to the transmitter; and
at the transmitter,
decoding and controlling the transmission of said low priority partition to
the receiver in response to a received control command request.
12. The method of claim 11 wherein the control command request is selected
from a group of commands including at least stop, pause, fast forward, and
replay commands.
13. The method of claim 2 further including the steps of
at the receiver, sending a replay command to the transmitter requesting a
replay transmission of the low priority partition;
at the transmitter, in response to the replay command, sending a replay
transmission of the low priority partition to the receiver; and
at the receiver, interleaving in real time a high priority segment
associated with each received low priority segment of the replay
transmission received from the transmitter.
14. The method of claim 2 wherein
the high priority information is a high priority partition including the
high priority segments and wherein at the receiver the high priority
partition is stored prior to receiving the low priority partition.
15. The method of claim 2 wherein
the high priority information includes standard format information used by
a receiver to generate the high priority segments.
16. The method of claim 2 wherein
the high priority information is used to identify high priority segments
previously stored at the receiver.
17. A method of communicating a video bitstream, including interleaved high
priority and associated low priority segments, over a packet network,
comprising the steps of
partitioning segments of a received video bitstream into high priority and
low priority partitions;
transmitting the high priority partition first over the network in real
time using a reliable delivery mechanism of the network;
subsequently transmitting, after the completion of transmission of the high
priority partition, the low priority partition second over the network
using a less reliable delivery mechanism of the network;
recovering and storing at a receiver location the high priority partition;
receiving the low priority partition at the receiver location; and
interleaving segments of the stored high priority partition in real time
with associated segments of the received low priority partition to
recreate the video bitstream.
18. Apparatus for transmitting a video bitstream from a transmitter over a
facility to a receiver, the video bitstream including a plurality of high
priority segments and associated low priority segments, said apparatus
comprising
at the transmitter,
first means for transmitting a high priority partition, including the high
priority segments, of the video bitstream over the facility using a first
packet delivery mechanism having a first probability of success;
second means for transmitting, after the completion of transmission of the
high priority partition, a low priority partition, including the low
priority segments, of the video bitstream over the facility in real time
using a second packet delivery mechanism having a second probability of
success which is substantially lower than that of the first delivery
mechanism; and
at the receiver,
means for receiving the high priority and low priority partitions;
means for storing the high priority partition; and
means for interleaving a high priority segment, obtained from storage, in
real time with the associated low priority segment to create an
interleaved video bitstream.
19. Apparatus for transmitting a video bitstream over a facility to a
receiver, the video bitstream including a plurality of high priority
segments and associated low priority segments, said apparatus comprising
first means for transmitting a high priority partition, including the high
priority segments, of the video bitstream, over the facility using a first
packet delivery mechanism having a first probability of success; and
second means for transmitting, after the completion of transmission of the
high priority partition, a low priority partition, including the low
priority segments, of the video bitstream over the facility in real time
using a second probability of success which is substantially lower than
that of the first delivery mechanism.
20. Apparatus for receiving a video bitstream over a facility from a
transmitter, the video bitstream including a plurality of high priority
segments and associated low priority segments, said apparatus comprising
means for first receiving the high priority partition and, after the
completed reception of the high priority partition, receiving the low
priority partition;
means for storing the high priority partition; and
means for interleaving a high priority segment, obtained from storage, in
real time with the associated low priority segment to create an
interleaved video bitstream.
21. A method of transmitting a video bitstream from a transmitter over a
facility to a receiver, the video bitstream including a plurality of high
priority segments and associated low priority segments, said method
comprising the steps of
at the transmitter, first transmitting standard format information, instead
of the high priority segments of the video bitstream, over the facility
using a first packet delivery mechanism having a first probability of
success, the standard format information being used to generate high
priority segments at the receiver;
subsequently transmitting, after the completion of transmission of the
standard format information, a low priority partition, including the low
priority segments, of the video bitstream over the facility in real time
using a second packet delivery mechanism having a second probability of
success which is substantially lower than that of the first delivery
mechanism; and
at the receiver,
receiving the standard format information and using it to generate the high
priority segments;
receiving the low priority partition; and
interleaving each generated high priority segment in real time with the
associated received low priority segment to create an interleaved video
bitstream.
22. Apparatus for transmitting a video bitstream from a transmitter over a
facility to a receiver, the video bitstream including a plurality of high
priority segments and associated low priority segments, said apparatus
comprising
at the transmitter,
first means for transmitting high priority information, representative of
the high priority segments, over the facility using a first packet
delivery mechanism having a first probability of success;
second means for transmitting, after the completion of transmission of the
high priority information, a low priority partition, including the low
priority segments, of the video bitstream over the facility in real time
using a second packet delivery mechanism having a second probability of
success which is substantially lower than that of the first delivery
mechanism; and
at the receiver,
means for receiving the high priority information and using it to generate
the high priority segments;
means for receiving the low priority partition; and
means for interleaving each generated high priority segment in real time
with the associated received low priority segment to create an interleaved
video bitstream.
23. The apparatus of claim 22 wherein
the high priority information includes standard format information used by
a receiver to generate the high priority segments.
24. The apparatus of claim 22 wherein
the high priority information is used to identify high priority segments
previously stored at the receiver.
25. A method of transmitting a video bitstream over a facility to a
receiver, the video bitstream including a plurality of high priority
segments and associated low priority segments, said method comprising the
steps of
first transmitting high priority information, representative of the high
priority segments, over the facility using a first packet delivery
mechanism having a first probability of success, the high priority
information being used to generate a high priority partition at the
receiver; and
second transmitting, after the completion of transmission of the high
priority information, a low priority partition, including the low priority
segments, of the video bitstream over the facility in real time using
second packet delivery mechanism having a second probability of success
which is substantially lower than that of the first delivery mechanism.
26. A method of receiving a video bitstream over a facility from a
transmitter, the video bitstream including a plurality of high priority
segments and associated low priority segments, said method comprising the
steps of
receiving the high priority information and using it to generate the high
priority segments;
receiving, after the completion of reception of the high priority
information, the low priority segments; and
interleaving each generated high priority segment in real time with the
associated low priority segment to create an interleaved video bitstream.
27. Apparatus for transmitting a video bitstream over a facility to a
receiver, the video bitstream including a plurality of high priority
segments and associated low priority segments, said apparatus comprising
first means for transmitting high priority information, representative of
the high priority segments, over the facility using a first packet
delivery mechanism having a first probability of success, the high
priority information being used to generate the high priority segments at
the receiver; and
second means for transmitting, after the completion of transmission of the
high priority information, a low priority partition, including the low
priority segments, of the video bitstream over the facility in real time
using a second packet delivery mechanism having a second probability of
success which is substantially lower than that of the first delivery
mechanism.
28. Apparatus for receiving a video bitstream over a facility from a
transmitter, the video bitstream including a plurality of high priority
segments and associated low priority segments, said apparatus comprising
means for receiving the high priority information and using it to generate
the high priority segments;
means for receiving, after the completion of reception of the high priority
information, the low priority segments; and
means for interleaving each generated high priority segment in real time
with the associated low priority segment to create an interleaved video
bitstream. |
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Claims |
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Description |
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Related subject matter is disclosed in the following application filed
concurrently herewith and assigned to the same assignee hereof: U.S.
patent application Ser. No. 08/341787, pending, entitled "Method Of And
Apparatus For Video Bitstream Transmission Over Packet Networks,"
inventors G. L. Cash and M. R. Civanlar.
TECHNICAL FIELD
This invention relates to video transmission and, more particularly, to a
technique for transmitting compressed previously stored video over lossy
packet networks in real time so as to reduce the effects of packet losses
on the quality of the received video.
BACKGROUND OF THE INVENTION
Transmission of stored compressed video over lossy packet networks has a
number of important applications including movies-on-demand, interactive
television, and corporate educational video distribution. Most of the
present and planned packet networks, particularly Asynchronous Transfer
Mode (ATM) networks, exhibit packet loss. Since compression reduces
redundancy in the video signal, losing random parts of a compressed video
bit-stream may cause drastic reduction in the quality of the received
video. It is a continuing problem to improve the quality of video
transmission over such packet networks.
SUMMARY OF THE INVENTION
The present invention discloses apparatus and method of transmitting a
video bitstream from a transmitter over a packet network to a receiver,
the video bitstream including a plurality of high priority segments (high
priority pertition) and low priority segments (low priority pertitions).
The high priority segments contain vital control information such as the
codes that define the start of pictures and picture header information.
The low priority segments contain the rest of the bitstream. As an
example, the high priority and low priority segments may be determined in
accordance with the well-known MPEG-2 draft standard (see Generic Coding
of Moving Pictures and Associated Audio, Recommendation H.262, ISO/IEC
13818-2, March 1994). In the present invention, the high priority
information, representative of the high priority segments, is sent first
over the network using a guaranteed delivery mechanism of the network;
thereafter the low priority partition is sent in real time over the
network using a non-guaranteed delivery mechanism. At a receiver location,
the high priority information is received and used to generate the high
priority segments. When the low priority partition is received at the
receiver location, its segments are interleaved with each generated high
priority segment, in real time to recreate the video bitstream.
The high priority information may be sent as a high priority partition,
sent as a high priority format used by the receiver to generate a high
priority partition, or sent as a high priority identifier used to identify
a high priority partition previously stored at the receiver.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows our inventive method for the transmission of high and low
priority segments;
FIG. 2 shows our illustrative client server video distribution network
useful in understanding the present invention;
FIG. 3 shows various formats for storing video bitstreams in a disc at the
server location;
FIG. 4 is a flowchart describing the server and client interactions for
handling video segment requests; and
FIG. 5 shows Table 7-28 of the MPEG-2 draft standard illustrating priority
break points; and
FIG. 6 shows examples of high priority formats.
DETAILED DESCRIPTION
With reference to FIG. 1, we describe how the present invention is used for
the transmitting of high and low priority portions of video information
over a packet network. Analog video signals associated with each video
program (or video segment) are received in the standard NTSC, PAL, etc.,
formats, digitized in digitizer 105, compressed in compressor 110 and the
resulting compressed video bitstream is stored in a disc 115.
Illustratively, the well-known format of a video bitstream of a video
segment is shown by 120. As shown, the illustrative video bitstream data
for a video segment includes a plurality of high priority (e.g., HP1) and
low priority (e.g., LP1) segments. In an encoded bitstream, the partition
boundaries (e.g., that between HP1 and LP1) cannot be determined without
some processing. This "data partitioning" is described in the
above-identified MPEG-2 standard as a technique that splits a video
bitstream into two layers called partitions. A priority breakpoint
indicates which syntax elements are placed in partition 0, which is the
base partition (also called high priority partition). The remainder of the
bitstream is placed in partition 1 (which is also called low priority
partition). The interpretation of " priority.sub.-- breakpoint" is given
in Table 7-28 on page 113 of the MPEG-2 standard, which is reproduced
herein as FIG. 5.
In the prior art, when a request for a video segment is received, the video
bitstream 120 is obtained from storage 115 and processed by a priority
transmitter unit (not shown in FIG. 1) so that the high priority video
partition (e.g., segments HP1-HPn) is sent over a high priority channel of
a transmission facility and the low priority partition (e.g., segments
LP1-LPn) is sent over a low priority channel of the facility. In such an
arrangement, the high priority channel is typically one having a high
probability of delivery, while the low priority channel is one having a
substantially lower probability of delivery. Undesirably, facilities which
connect to a packet network may only have channels which operate at one
error rate. In such an arrangement, the prior art techniques may not be as
useful.
In accordance with the present invention, server processor 130 determines
if the high priority information sent to the clients should be sent using
the high priority segments themselves (steps 132, 133), sent using a high
priority format (steps 132, 134, 135), or sent using a high priority
identifier (steps 132, 134, 136) which identifies a previously stored high
priority partition at the client or receiver location. In one example,
when the high priority information is to be sent as the high priority
segments themselves (step 133), server processor 130 of the stored
bitstream 115 generates the high priority partition (311 of FIG. 3) and
the low priority partition (312 of FIG. 3). In such a case, the server
sends the high priority partition followed by the low priority partition
segments (step 137) to the client location. As noted, the server may also
send the high priority information in the form of a high priority format
(step 135, see FIG. 6) or a high priority identifier (step 136) followed
by the low priority partition (step 137) to the client location.
With reference to FIG. 2, we describe an illustrative server/client network
in which the present invention may be utilized. Such a network includes a
server location 200 which connects via packet network 210 to a plurality
of clients 220-230. Server location 200 includes a video-on-demand
server/processor 201 which controls the operation of the hard disc 202 and
network interface 203. The hard disc 202 is used to store the compressed
video bitstreams utilizing one or more of the formats shown in FIG. 3. It
should be noted that all of the compressed video data stream need not be
stored locally on disc 202, but may be remotely stored, as part of a
remote file server, and accessible via facility 204 (e.g., a local area
network).
The network interface 203 is utilized to transmit and receive using the
protocols required by the packet network 210. The processor 201 performs
the functions illustrated at the server portion of the flowchart of FIG.
4.
The packet network 210 may be an Asynchronous Transfer Mode (ATM) network,
an FDDI, Ethernet or other similar packet networks.
A client location, e.g., 220, includes a network interface 223 for
converting communication protocols received from and transmitted over a
facility connected to packet network 210. A disc 222 is used to store the
high priority portion of the video bitstream received by network interface
223. The video client processor 221 processes the received video bitstream
in accordance with the client functions illustrated in the flowchart of
FIG. 4. Processor 221 interleaves the high priority data received from
disc 222 with the low priority data received by network interface 223 and
then sends the interleaved data to decoder 224. The output of decoder 224
is the requested video segment which is then displayed on the client
monitor 225.
Similarly, client 230 includes processor 231, disc 232, network interface
233, decoder 234 and monitor 235.
With reference to FIG. 3, we describe the various formats for storing video
bitstreams representing data of video segments 1 through n.
Shown by 310 is the raw compressed data stream for video segments 1-n,
where the high priority and low priority portions are HP1-HPn and LP1-LPn,
respectively. In the raw compressed data stream, the separation between
the high priority (e.g., HP1) and low priority (e.g., LP1) data portion
can be defined based on priority breakpoints. These priority breakpoints
can have a variety of values as shown in FIG. 5 which illustrates Table
7-28 of the previously referenced MPEG-2 standard. In accordance with the
present invention, the network server can be arranged to handle any of the
breakpoint values shown in Table 7-28 (FIG. 5). When data is stored as a
raw compressed data stream, the network server 200 must first identify the
video segment requested by a client and then process the data stream
associated with that requested segment using the particular breakpoint
value to identify the high priority data segments. It should be noted that
the division between the high priority and low priority partitions varies
with the particular video segment and the type of priority breakpoint (see
Table 7-28 of FIG. 5) utilized for partitioning. Illustratively, in one
embodiment the high priority data portion HP1 includes those data items of
priority breakpoint 1 shown in Table 7-28 of FIG. 5.
Generally, any of the priority breakpoints of FIG. 5 can be sent as part of
the high priority partition (133 of FIG. 1 ). However, only priority
breakpoints 0-1 would be used if a high priority format (135 of FIG. 1 )
or high priority identifier (136 of FIG. 1) is used as the high priority
information sent to the client.
Hence, with reference to FIG. 3, HP1 would include sequence start, GOP and
picture header 1. The picture header also includes a time or frame
identifier. The sequence start header includes data defining the vertical
and horizontal resolution of the video segment. A video segment includes
multiple pictures (or frames). The picture (or frame) rate may be from 24
per second for motion pictures to 30 per second for broadcast television.
Each picture (or frame) may include a plurality of slices. The GOP data is
optional, and includes the picture coding utilized for the segment. The
picture header 1 includes the header information for all slices of picture
1 (or frame 1). The low priority data portion LP 1 includes the rest of
the bitstream for picture 1. Additionally, in accordance with the present
invention, the low priority data portion LPI may include time and frame
identifiers corresponding to that of HP1. Similarly, each of the high
priority data portions HP2 through HPn include at least the headers for
the slices of the associated picture. The length of each video segment may
be different and have a different number of high priority and low priority
data portions within each segment. Note that the size of the low priority
data portions LP1-LPn may be different lengths due to picture content.
After identifying these high priority data portions HP1-HPn, network server
200 then forms the high priority and low priority data segments shown,
respectively, by 311 and 312. Shown by 320, the data for video segment 1
has been processed into a high priority data partition 311 and a low
priority data partition 312 and stored on disc 202. This processing of the
data may be done by server 200 or the data may be received in processed
form by server 200 and downloaded to disc 202. Similarly, the data
associated with video segments 2 through n have also been stored after
having been partitioned into high priority and low priority data portions.
When the data or video segments 1-n are stored using the format 320, then
the network server 200 need only transmit the high and low priority
partitions of the requested segment to the client without further
processing. Thereafter, the server 200 outputs the requested video segment
to the client in the format shown by 320.
Shown in 330 is another format for storing video segment bitstreams. This
format uses the raw compressed data streams of 310 together with a table
338 which preferably identifies the disc location and time stamp or frame
identification for each high priority data portion of each video segment.
Alternatively, the length of the high and low priority data portions or
perhaps a time stamp or frame identification for each high priority data
portion may also be stored in the table 338. Using the format shown in
330, server 200 can quickly form the high priority data segment 311 and
low priority segment 312 using the table entries to quickly locate the
high priority data portions HP1-HPn stored on disc 202. Consequently,
server 200 can process a requested video segment by a client in real time
and output a data stream of the requested video segment to the client in
the format shown by 310.
Alternatively, server 200 can send high priority information using high
priority format 340 or high priority identifier 341. This high priority
information is used by the receiver to generate a high priority
partition--that is, in our example shown in Table 338, either an
international standard, if one exists, or a format previously agreed-to by
the client and server 200.
Another implementation may use a high priority identifier to identify which
of several previously stored high priority partitions available at the
client receiver is to be interleaved with the low priority partition to
reconstruct the original video bitstream. In such an embodiment, the high
priority information sent to the client would include either the
appropriate high priority format or identifier information.
With reference to FIG. 6, we illustrate an example of a high priority
standard format which may be sent from the server 200 to the client. As
shown by 601, the format includes an M and N number and MPEG-2 picture
level information. As shown, the MPEG-2 picture level information includes
an I and, optionally, a P and/or B frame. As shown, the M specifies the
number of B frames between P or I frames+1 and N specifies the number of B
or P frames between I frames+1, where I is the intra-coded frame, B is the
bidirectional coded frame, and P is the predictive coded frame. Shown in
602 are several examples of different M and N values for high priority
formats 1, 2 and 3.
With joint reference to FIGS. 2, 3 and the flowchart of FIG. 4, we describe
the server and client interaction for handling video segment requests from
a client.
In step 400, server 200 is in a wait state, waiting for a client request.
In step 401, a client 220 requests a particular video segment. In step
402, network server 200 receives a client's video segment request. In step
403, server 200 reads the high priority format or reads the high priority
identifies for the entire requested segment. Thus, for example, if the
data for a video segment was stored in the format 320, then server 200
need only read out the high priority segment 311 from disc 202. However,
as previously described, if data for the requested video segment was
stored, or received from a remote file server, in its raw compressed data
form, server 200 must process that data to create the high priority data
segment 311 from the individual high priority data items HP1 through HPn
of 310 of FIG. 3. Even though a video segment is received in its raw
compressed data form, it may still be sent to the client in real time. For
example, the desired video segment may be broken into multiple
sub-segments, each with its own high priority 311 and low priority 312
partitions. Server 200 may then provide an elastic first-in-first-out
buffer (p/o processor 201) to store at least one sub-segment. The
transmission of the first sub-segment is delayed by at least one
sub-segment's time period, so that server 200 can set up the HP partition
311 and LP partition 312 for the first sub-segment. Thereafter, while the
first sub-segment is being transmitted to the client, the next sub-segment
is being received and processed by server 200. In this manner, the HP and
LP partitions 311 and 312 can be formed and transmitted to the client in
real time from the received raw compressed data stream.
Alternatively, if data for the requested video segment was previously
stored in disc 202 in the format 330, then server 200 would utilize table
338 to identify in real time the high priority data partition in the data
stream of the requested video segment. Using either 1) the high priority
data of the requested video partition 311 stored in disc 202, or 2) the
processed raw compressed data stream which is formatted into the high
priority data partition 311 or 3) by using table 338 together with the raw
compressed data stream to generate the high priority data partition 311 in
real time, server 200 prepares the high priority data for the requested
video segment for transmission to the requesting client. Alternatively, as
previously noted the server 200 can send information in the form of the
high priority data itself, high priority format information, or a high
priority identifier, depending on the implementation of the client/server
network. In step 404, server 200 selects a packet network 210
communication protocol which ensures guaranteed delivery of the high
priority information over the packet network 210 to the requesting client.
The communication protocol for guaranteed delivery would, of course, be
one that is specified by packet network 210. Such communication protocols
for guaranteed delivery are well known in the art. For example, see
"Reliable Stream Transport Service (TCP), Chapter 12 of the book by D. E.
Comer entitled Internetworking with TCP/IP, Volume 1:Principles, Protocols
and Architecture, Second Edition, Prentice Hall, 1991. Typically, such a
communication protocol for guaranteed delivery involves the sending of
data packets with error detection and, possibly, error correction
capability to the client. The client would then, typically, after
receiving the packet send an acknowledgement message back to the server
200. This acknowledgement message would indicate to server 200 whether
client 220 has received the packet with errors or error-free. This
acknowledgement message can also be used to alert the server 200 when an
out-of-sequence data packet has been received by client 220. If no
acknowledgement message is received by server 200 within a predetermined
time, server 200 would re-send the data packet.
In step 405, client 220 sets itself to receive using the communication
protocol for guaranteed reception and signals the server 200 that it is
ready to receive data packets. In step 406, server 200 sends all of the
high priority data to client 220. In step 407, for our example the client
receives the high priority data. The previously described communication
protocol for guaranteed delivery ensures that the client 220 has received
the high priority data error-free from the server 200. In step 408, client
220 stores the high priority data. Note, because the HP partition
(HP1-HPn) generally represents approximately 0.2 percent of all of the
data for a selected video segment, it can easily be stored on the disc
(e.g., 222) at the client location. In comparison, the LP partition
(LP1-LPn) for a typical movie video segment would be too large (typically
several gigabytes) to be practical for storage at the client location.
Because of the low-cost wideband transmission network 210 available, the
LP partition can be readily retransmitted any time that the client wants
it.
If the high priority information was in the form of a high priority format
or identifier, then in steps 407 and 408 they would be received and
stored. Alternatively, in step 408 the high priority format may be
utilized to generate the high priority partition information which would
then be stored.
In step 409, the server 200 sets the communication protocol for
non-guaranteed delivery of the low priority data of the requested video
segment to the client 220. In accordance with an aspect of the present
invention, the system can limit the number of times that the low priority
data of the requested video segment can be sent to the client 220. This
ability to multiply send the low priority partition 312 to the client 220
enables the client to have a capability to pause or rewind during the
reception of a video segment without having to again receive the high
priority partition 311.
In step 410, client 220 sets a communication protocol for the
non-guaranteed reception of the low priority partition. The client 220
knows to set the non-guaranteed protocol when it receives an
end-of-high-priority flag as part of the high priority data reception
during step 407.
In step 411, server 200 reads from disc 202 the low priority data partition
312, when format 320 is utilized (or creates the low priority data
partition 312 when format 310 or 330 is utilized, as previously
described). In step 412, server 200 transmits the low priority data
partition 312 in real time to client 220. The packets containing the LP
data may include frame numbers, time stamps, sequence numbers enabling
resynchronization to the associated HP data at the client decoder 224 in
the case of LP packet loss.
In step 413, in our example client 220 reads the high priority partition
from memory and, in step 414, sends it to video decoder 224.
Alternatively, if a high priority identifier was stored in step 408, it
would be used to access the high priority partition at the client
location. If, however, the high priority format information was stored in
step 408, then in step 413 it could be used to generate the high priority
partition.
In step 415, client 220 receives the low priority data segment in real time
from server 200 and sends it in step 416 to video decoder 224. The steps
414 and 416 are coordinated by processor 221 so that the stored high
priority partition is interleaved in real time with the received low
priority partition sent to video decoder 224. The interleaved data would
have the original raw compressed data stream format shown by 310. Video
decoder 224 then converts the interleaved data to the display format
needed to enable monitor 225 to display the requested video segment.
In step 417, client 220 can request to replay the video segment. If a
control command request is made, in step 418, control returns to step 411.
A control command request may be the well-known VCR-type request including
stop, pause, fast forward, fast backward, replay, etc. The stop command
instructs the server 200 to not send any additional low priority data. The
pause command performs the stop command function but additionally causes
decoder 224 to hold the last frame. The fast forward command causes server
200 to send only MPEG-2 I frames of the low priority partition. The fast
backward command causes the server 200 to send the I frames in reverse
order. The replay command causes server 200 to re-send only the low
priority partition. These capabilities may illustratively be implemented
consistent with the "Trick modes" described in section D.12 at page 167 of
the previously referenced MPEG-2 draft standard.
If the control command requests a new video segment, step 419, control
returns to step 402. If no control command request is made, step 420, then
processor 221 clears the previously stored high priority data from memory.
In step 421 the procedure ends and control returns to the standby state,
step 400.
While the present invention has been described for an encoded video
bitstream, it can more generally be used with unencoded video bitstreams.
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