Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1996-12-20
2001-03-13
Kelley, Chris S. (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06201834
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to a method and apparatus for correcting packet loss in a standard-based packet video system. More particularly, the present invention pertains to monitoring a packet-loss event and correcting such an event.
A typical video communication system
10
that is known in the art is shown in FIG.
1
. The system
10
allows communication between the systems of User A
11
and User B
13
via a transmission medium or network
12
(e.g. a so-called Ethernet network). In this example, the system at User A
11
includes a processor
15
, such as a Pentium® processor manufactured by Intel Corporation, Santa Clara, Calif., executing code stored in memory
19
. A video system
17
is provided that captures and compresses video image data for transmission over the network
12
to the station at User B
13
. In this example, the video subsystem
17
is coupled to the processor
15
via a first bus
16
such as one operated according to the Peripheral Component Interconnect (PCI) (Version 2.1, 1995, PCI Special Interest Group, P.O. Box 14070, Portland, Oreg., 97214). The video subsystem is also responsible for decompressing video images received from the system at User B
13
. The network
12
is coupled to an Ethernet network interface
21
which handles the sending of digital video information from the video subsystem over the network
12
. The network interface
21
is coupled to the video subsystem
17
and the PCI bus
16
via an ISA (Industry Standard Architecture) bus
20
and a bridge circuit
18
.
Referring to
FIG. 2
, a exemplary video subsystem
17
that is known in the art is shown. The video subsystem is typically run by an application
30
(e.g., a program stored in memory
19
and executed by the processor
15
in FIG.
1
). A camera
31
is provided that generates video image data for a video capture component
33
. The video capture component
33
“captures” the video image data from the camera one frame at a time in a known manner and at a predetermined rate (e.g., approximately 30 frames per second). The video capture component
33
transfers the video frame data to a video coder/decoder
35
which typically includes a coder/decoder (codec)
36
that compress the video image data for the frame. Typical compression algorithms include any of a variety of block transform based video compression algorithms such as H.261 (International Telecommunication Union—Telecommunications Standardization Sector (ITU-T), March, 1993), H.263 (ITU-T, Dec. 5, 1995), JPEG (“Joint Photographic Expert Group”)(International Organization for Standardization/International Electrotechnical Commission (“ISO/IEC”) 10918-1), MPEG-I and MPEG-II (“Motion Picture Expert Group”)(ISO/IEC 11172-2 and 13818-2). In these block transform based video compression algorithms, the uncompressed video frame data is divided into groups of blocks (GOB) (e.g., 16 horizontal lines of pixels for each group of blocks). Each GOB is divided into a sequence of macroblocks (e.g., 16×16 pixel blocks), each defining a spatial area of the video frame. Each macroblock is compressed using one of the aforementioned algorithms in the coder portion of the codec
36
.
The video coder/decoder
35
passes each compressed video image data for each frame to a packet preparation module (PPM) payload handler (“payload handler”)
37
which fragments the compressed video image data into packets which each include a number of macroblocks. The appropriate protocol information is added to one or more packets (e.g., according to the so-called Real-Time Transport Protocol (RTP) defined by the Internet Engineering Task Force (IETF)) for transport over the transmission medium. The packets, with the appropriate protocol layer, are then ready to be transported over the network
12
to User B
13
.
Packets from User B
13
, for example, are received at the payload handler
37
where the RTP protocol information is assessed and “stripped off.” The compressed video image data in the packets is ascertained and transferred to the codec
36
in the video coder/decoder
35
. The decoder portion of the codec
36
creates uncompressed video image data which can be displayed at a display
39
such as a cathode ray tube (CRT) or active matrix flat-screen under the control of the application
30
.
In the system
10
of
FIG. 1
, packets of information can be lost or the contents of a packet could be in error (e.g., during transmission over the network
12
). Systems such as the Video for Windows® (VfW) system and video applications used in the UNIX operating system handle packet loss by skipping the processing of such a packet and continue processing on the next uncompromised packets. Such systems have disadvantages in that by ignoring the lost packet, the relationship between the other packets is compromised leading to errors in what is displayed. Also, errors that occur due to ignoring the lost packet are propagated to other packets that use prediction to determine video image data.
SUMMARY OF THE INVENTION
According to the apparatus and method of the present invention, a first video coder/decoder is provided which receives uncompressed video frame data and generates a first compressed bitstream based on a compression algorithm. A first payload handler coupled to the video coder/decoder fragments the first compressed bitstream into a sequence of packets and appends a transport header to at least one packet identifying the packet in the sequence of packets. A second payload handler is coupled to the first payload handler via a transmission medium, and determines from the transport header whether any of the packets are lost. The second payload handler generates a second compressed bitstream including video frame data from the packets, and appends a bitstream information stream to the second compressed bitstream. The bitstream information stream indicates parameters for decompressing the first compressed bitstream according to a predetermined protocol and places replacement compressed bitstream data in the second compressed bitstream in place of video frame data in the lost packet. A second video coder/decoder is coupled to the second payload handler and generates uncompressed video image data from the replacement compressed bitstream data based on the bitstream information stream.
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Intel Corporation
Kelley Chris S.
Kenyon & Kenyon
Philippe Gims
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