Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-12-16
2004-05-25
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06741656
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image communication apparatus for transmitting and receiving dynamic images, still images, audio signals, and others, and more particularly to synchronization of timing when transmitting and receiving by inserting preliminarily accumulated dynamic images and still images into real-time dynamic images and still images.
BACKGROUND OF THE INVENTION
FIG. 1
is a structural diagram showing a standard H.324 terminal device in which ITU-T Recommendation H.324 is applied as a prior art.
In
FIG. 1
, crude data such as audio data, video data, and control data generated by microphone, camera, and system in a standard transmission capacity generation unit
101
having a standard transmission capacity of H.324 are encoded in audio encoder, video encoder, and control encoder, respectively. Using transmission protocols of AL2, AL3, SRP corresponding to the encoded data, they are issued as a bit stream
104
of audio encoded data, a bit stream
105
of video encoded data, and bit stream
106
of connection control encoded data. From an application specification storage unit
102
for storing an application specification for using a non-standard capacity, a bit stream
107
of data is issued through a protocol storage unit
103
for storing a transmission protocol of data channel. A multiplexer
108
assembles bit streams
104
to
107
into one packet, and sends out to a transmission path
113
as multiplexed data. A demultiplexer
109
separates the multiplexed data transmitted through the transmission path
113
into individual bit streams. Separated bit streams of video encoded data and connection control encoded data are received in a standard reception capacity generation unit
110
having a standard reception capacity of H.324 by using reception protocols corresponding to AL2, AL3 and SRP, and are respectively decoded in an audio decoder, a video decoder, and a control decoder, and issued to speaker, display unit, and system as audio data, video data, and control data. Data of non-standard capacity is issued to an application specification storage unit
112
for storing an application specification for using non-standard capacity through a protocol storage unit
111
for storing a reception protocol of data channel of non-standard capacity.
The standard H.324 terminal device shown in
FIG. 1
is composed of three channels, that is, a control channel for managing the connection information between terminal devices, a dynamic image channel for transferring a dynamic image bit stream encoded in real time, and an audio channel for transferring an audio bit stream encoded in real time. For such data transfer, a standard specific transfer protocol designated by ITU-T Recommendation is used, and therefore exchange of real-time sound, real-time dynamic image and connection information is possible among all terminal devices.
If other functions than such standard functions are required, a data channel having a transfer protocol for such function (a protocol stored in the protocol storage unit
103
) is needed, and it also requires an application specification for using such data (an application specification stored in the application specification storage unit
102
). There are various types of transfer protocol and application specification depending on the purpose. It is, however, not always guaranteed that the terminal device at the destination side has the same protocol and specification as possessed at the sender's side. Accordingly, at the time of start of connection, using the control channel, it is judged if usable or not by mutually checking the additional functions provided in the individual terminal devices.
In a television conference system, real-time video and audio are entered at the same time. Being encoded in the individual encoders, video and audio bit streams issued from encoders are immediately sent into the multiplexer, and the multiplexed bit stream is transmitted to the terminal device at the destination. Since they are immediately multiplexed after generation and transmitted, the synchronism of video and audio is maintained. However, the required encoding time differs between audio and video signals, and if put in the same time width, video encoding takes a longer time than audio encoding. If mixed right after generation of data, synchronization is actually deviated by the portion of this time difference.
Incidentally, the video bit stream designated, for example, in H.263 has time information TR of absolute time for turning one round in every eight seconds approximately in order to indicate the display start time of the image in every frame. The transmission side has a time counter for turning one round in every eight seconds, and on the basis of this time counter, the time information TR is inserted in each frame in the bit stream. The decoder adjusts the display changeover timing of each frame for composing a dynamic image on the basis of the time axis managed by itself and the time information TR in the video frame.
Problems occurring when inserting preliminarily accumulated images into real-time images are discussed below while referring to an example of television conference system.
FIG. 2
(
a
) shows the stream state of encoder and decoder, and the stream state of accumulated video data when passing accumulated video data in video channels in the conventional television conference system, and
FIG. 2
(
b
) shows the display timing of each frame when changing over from the real-time image to accumulated image.
In
FIG. 2
, reference numeral
201
shows a first frame of accumulated video data, and
202
shows a last frame of real-time video data issued from an encoder. Reference numeral
203
shows the display start position of last frame of real-time video data issued from the encoder, and
204
is the display start position of first frame of accumulated video data.
In the television conference system, when changing over from the video bit stream flowing in the video channel to the accumulated video bit stream, the difference between the time information TR (
202
) of the last frame
202
of the real-time dynamic image bit stream, and the time information TR (
201
) of the first frame
201
of the accumulated video bit stream is the time width from he display start point
203
of the last frame of the real-time dynamic image on the decoder till the display start point
204
of the first frame of the accumulated image. In the example in
FIG. 2
(
b
), the time width
205
from the display start point
203
of the last frame of the real-time dynamic image till the display start point
204
of the first frame of the accumulated image is variable with the changeover timing, and it may be about eight seconds at worst, and in this period, therefore, the real-time last image is displayed as a still image.
In the conventional television conference system, for the purpose of strict synchronization, the synchronization deviation information called skew is transmitted to the terminal device at the destination separately through a control channel, and by adjusting the synchronization by its value, strict synchronization of video and audio is realized on the terminal device at the destination.
In the television conference system, while transmitting the dynamic image in real time, it is often changed over to preliminarily accumulated images (dynamic image or still image) on the way. For example, if attempted to transmit an accumulated still image by using a dynamic image channel according to the H.263 regulation, the image bit stream designated in the H.263 is variable in the time difference between the time information TR of the last frame of the bit stream of the dynamic image immediately before changeover, and the time information TR of the first frame of the accumulated image bit stream, when changed over from the image bit stream flowing in the video channel in the real time to the accumulated image bit stream, and, depending on the circumstance, there is a considerably long waiting time until reproduction o
Kelley Chris
RatnerPrestia
Senfi Behrooz
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