JP4630357B2 - Video transmission / reception system and control method thereof - Google Patents

Description

  The present invention relates to a video transmission / reception system and a video switching method, a video transmission / reception system, a video switching method, a video transmission device, a video reception device, and a control device, and in particular, one of a plurality of video transmission devices in video relay / transmission. Video transmission / reception system and video switching method for preventing video signal interference and temporary omission when switching received video to video from another video transmission device The present invention relates to a video switching method, a video transmission device, a video reception device, and a control device.

  In a conventional video playback system in which there are a plurality of video transmission devices connected to video sources such as cameras and VTRs, and one of them is played back, a video signal is always output from each video transmission device. Thus, a technique such as electrical switching by a video switching device is taken. For example, there is a method of performing analog / digital conversion of a video signal, buffering video data using a memory, and maintaining synchronization during video switching (see, for example, Patent Document 1).

  In addition, there is a technique in which video switching devices are connected in multiple stages and one video is selected from a number of video transmission devices and played back (see, for example, Patent Document 2).

  In addition, there is a system in which a video transmission device and a video reproduction device are connected via a network, and each video is transmitted as a plurality of encoded streams (see, for example, Patent Document 3).

Furthermore, there is a technique in which videos on a plurality of servers existing on a network are sequentially transmitted by a VOD (video on demand) method, and are played back so that no video breaks occur in the video playback device (for example, (See Patent Document 4).
JP-A-6-253213 JP 2003-186460 A Japanese Patent Laid-Open No. 11-112964 Japanese Patent Laid-Open No. 11-41585

  However, in the conventional systems as shown in Patent Documents 1 and 2, the video transmission device and the video switching device must be directly electrically connected to each other. When there are a large number of video transmission devices and they are distributed at different positions, it is difficult to electrically connect each video transmission device and video switching device directly. On the other hand, when the multistage connection of the video switching device as in Patent Document 2 is used, if there is a transmission delay between the video playback device and the video switching device, it is difficult to switch the video at the time desired by the user. is there.

  In addition, as shown in Patent Document 3, the video transmission path is a packet-switched network and the video transmission device is used, so that the video transmission device and the video reproduction device can be connected even when the transmission distance is long. Becomes easier. However, in this case, if the total bit rate of the encoded stream exceeds the bandwidth of the transmission path, congestion occurs and video transmission cannot be performed correctly, so the number of connectable video transmissions or video quality is limited. .

  In Patent Document 4, only the encoded stream from one selected server among a plurality of servers serving as video transmission devices is transmitted, but at the moment of video switching, two encoded streams exist on the transmission path at the same time. Therefore, in order to avoid degradation of video quality due to congestion, the total bit rate of the two encoded streams must be smaller than the bandwidth of the transmission path. In packet-switched networks, switching is controlled so that packet arrival congestion does not occur. Transmission delay time between each video transmission device and the congestion occurrence point and packet arrival time fluctuation (jitter) Therefore, it is necessary to control the start / stop of video transmission of each video transmission device.

  The present invention has been made in view of the above points, and in a situation where there are a plurality of video transmission devices, the interference of video signals regardless of the number of video transmission devices, the location of the video transmission devices, and the transmission distance from the video reception / playback device. Video transmission / reception system, video switching method, video transmission / reception system, video switching method, video transmission device, and video reception capable of switching received video accurately at the time requested by the user without causing image quality degradation due to congestion or congestion An object is to provide a device and a control device.

  In order to solve the above problems, in the present invention, only one of a plurality of video transmission apparatuses performs video transmission to one video reception apparatus, stops video transmission of the video switching source, and switches the video switching destination. Video transmission is started and video switching is performed in the video receiver. Also, each video transmission device transmits the generated time code to the video reception device regardless of whether or not video transmission is performed, and the video reception device uses the time code difference from each measured video transmission device to the video transmission device. On the other hand, the video transmission start time is designated. The time code here is a value representing the time in the video signal, and is typically a SMPTE time code with one frame of the video signal as a minimum unit, but if it is time information synchronized with the input video signal. It can be anything.

According to claim 1 of the present invention, there is provided a video transmission / reception system in which a video reception device switches received video from one video transmission device to another video transmission device among a plurality of video transmission devices,
The video receiver is
Time code measuring means for measuring the time code received from the video transmission device with the accuracy of the number of video lines;
Based on the measured time code, the video transmission stop time code generating means for generating and transmitting the video transmission stop time code ET to the current video receiving destination video transmitting device, or the measured time code A video transmission start time code generating means for generating and transmitting a video transmission start time code ST to the video transmission device of the video switching destination,
The video transmission device includes:
Time code generation means for generating a time code T;
A transmission buffer for holding a video signal for a predetermined time;
When the ET is received, the buffer is controlled to stop buffering when T = ET, or when the ST is received and the frame numbers of T and ST are equal, the buffer is provided for the time corresponding to the ST line number SL. A buffer control unit for controlling the transmission buffer to start a ring;
Video transmission means for starting transmission from the video signal at the head of the transmission buffer to the video reception device after the SL time has elapsed.

According to claim 2 of the present invention, the video receiving device comprises:
A reception buffer that holds video for a predetermined time with respect to the input video;
A target value, an upper limit threshold value, and a lower limit threshold value of the amount of video signal in the reception buffer are set, and the number of excess lines exceeding the upper limit threshold and exceeding the target value, or the amount is lower than the lower limit threshold value. A buffer monitoring unit that monitors the number of insufficient lines below a target value and transmits the number of excess lines or the number of insufficient lines to the video transmission start time code generation unit;
The video transmission start time code generation unit obtains the ST based on the number of excess lines or the number of insufficient lines, the ET, and the measurement time code.

According to claim 3 of the present invention, the video transmission device comprises:
When the video signal in the transmission buffer becomes half of the predetermined crossfade time FT, the transmission bit rate is decreased stepwise or the normal bit so that the video signal in the transmission buffer is completed simultaneously with the FT. Video transmission fade-out means for performing video transmission with a constant bit rate lower than the rate, and then stopping video transmission;
After the SL time, the transmission bit rate is increased stepwise or a certain amount of bit rate lower than the normal bit rate so that video transmission for half the time of the FT is completed simultaneously with the FT. Video transmission fade-in means for starting video transmission while maintaining and buffering video signals for half the time of the FT.

According to a fourth aspect of the present invention, in a video transmission / reception system in which a video reception device switches received video from one video transmission device to another video transmission device among a plurality of video transmission devices, the transmission buffer of the video transmission device A method of controlling
The video receiver is
Measuring the time code received from the video transmission device with the accuracy of the number of video lines;
Based on the measured time code, a step of generating and transmitting a video transmission stop time code ET to the current video receiving destination video transmitting device, or based on the measured time code, a video switching destination Generating and transmitting a video transmission start time code ST to the video transmission device; and
The video transmission device includes:
Generating a time code T;
Holding a video signal for a predetermined time;
When the ET is received, the buffer is controlled to stop buffering when T = ET, or when the ST is received and the frame numbers of T and ST are equal, the buffer is provided for the time corresponding to the ST line number SL. Controlling the transmit buffer to initiate a ring;
After the SL time elapses, a step of starting transmission from the video signal at the head of the transmission buffer to the video receiving device is performed.

According to claim 5 of the present invention, the video receiving device comprises:
Holding a video for a predetermined time with respect to the input video;
A target value, an upper limit threshold value, and a lower limit threshold value are set for the amount of video signal in the reception buffer, and the number of excess lines exceeds the upper limit threshold value and exceeds the target value, or the amount is lower than the lower limit threshold value. Monitoring the number of insufficient lines below a target value, and transmitting the excess line number or the insufficient line number to the video transmission start time code generation unit;
Obtaining the ST based on the number of excess lines or the number of insufficient lines, the ET, and the measurement time code.

According to claim 6 of the present invention, the video transmission device comprises:
When the video signal in the transmission buffer becomes half of the predetermined crossfade time FT, the transmission bit rate is decreased stepwise or the normal bit so that the video signal in the transmission buffer is completed simultaneously with the FT. Performing video transmission while maintaining a certain amount of bit rate lower than the rate, and then stopping video transmission;
After the SL time, the transmission bit rate is increased stepwise or a certain amount of bit rate lower than the normal bit rate so that video transmission for half the time of the FT is completed simultaneously with the FT. Maintaining the video transmission and buffering the video signal for half the time of the FT.

  As described above, according to the present invention, even in a situation where there are a plurality of video transmission devices, regardless of the number of video transmission devices, the location of the video transmission devices, and the transmission distance from the video reception / playback device, The received video can be switched accurately at the time requested by the user without causing image degradation.

  First, the operation principle of the present invention will be described.

  FIG. 1 is a principle configuration diagram of the present invention.

The system of FIG. 1 includes a video receiving device and a plurality of video transmitting devices, and selects one of the plurality of video transmitting devices to receive a video. During this time, other video transmitting devices stop video transmission. A video transmission / reception system,
The video transmission device
Video input means;
Video transmission means for transmitting a video signal to a video receiver;
Time code generation means for generating a time code T;
Time code transmitting means for transmitting the time code T to the video receiver;
Video transmission stop means for receiving video transmission stop time code ET and stopping video transmission when T = ET or video transmission start time code ST is received, and video transmission is performed when T = ST Video transmission start means for starting
With
The video receiver
Video receiving means for receiving a video signal from a video transmission device via a transmission path;
Video output means;
Time code measuring means for obtaining a time code generated by the video transmission device;
Video transmission stop time code generating means for generating and transmitting a video transmission stop time code ET to the current video receiving destination video transmitting apparatus, or a video transmission starting time code ST for the video switching destination video transmitting apparatus Video transmission start time code generating means for generating and transmitting the video, and switching received video from a plurality of video transmission devices. The video transmission device and the video reception device may be implemented by a personal computer, a workstation, a dedicated computer, or any computer capable of executing the above-described functions.

  FIG. 2 is a diagram for explaining the principle of the present invention.

The method of FIG. 2 transmits a video transmission stop request to the video transmission device from the state in which the video reception device is receiving one of the video transmission devices, and transmits the video to another video transmission device. A video switching method for transmitting a start request and switching a received video,
In each video transmission device,
Generating a time code (step S1);
Performing a step (step S2) of transmitting a time code to the video receiver via the video transmission path regardless of whether or not the video is transmitted;
In the video receiver,
And step (step S3) for generating a video transmission stop time code ET _A,
A step (step S4) of transmitting ETA to the video transmission device A which is a video switching source;
Generating a time code OT _B and timecode OT _A difference DT _B to ET _A addition to video transmission start time code ST _B from the video transmission apparatus A from the video transmitting apparatus B that is measured by the video receiver (Step S5),
A step (step S6) of transmitting ST _B to the video transmission device B as a video switching destination;
In the video transmitting apparatus A, the step (step S7) receiving the ET _A,
Performs the step of the time code T _A which itself produced to stop at the same time video transmission becomes to ET _A (step S8), and the,
In video transmission device B,
Receiving ST _B (step S9);
A step (step S10) that the time code _{T B} which itself produces starts simultaneously video transmission becomes in ST _B,
The received video is switched from the video of the video transmission device A to the video of the video transmission device B.

  FIG. 3 is a diagram for explaining the operation principle of the video transmission start time code generation processing of the present invention.

The transmission paths of the two video transmission apparatuses A and B and the two video reception apparatuses are combined into one by the transmission path coupling apparatus 10 on the way. The transmission path coupling device 10 indicates a packet switching device in a packet transmission network, a device that electrically adds signals of two routes, and the like. When video transmission is performed simultaneously from each of the video transmission devices A and B, This is where congestion or video signal interference occurs. The time codes generated by the video transmission devices A and B are T _A and T _B , respectively, and the time codes from the video transmission devices A and B measured by the video reception device 20 are OT _A and OT _B , respectively. If the transmission delay time from A, B to the transmission path coupling device 10 is D _A , D _B , and the transmission delay time from the transmission path coupling device 10 to the video reception device 20 is DC,
T _A = OT _A + D _C + D _A (1)
T _B = OT _B + D _C + D _B (2)
This relationship holds. When the video transmission apparatus A performs control so that video transmission is stopped when T _A = ET _A and video transmission apparatus B is controlled to start video transmission when T _B = ST _B , The conditions for preventing congestion or interference in the transmission path coupler 10 are as follows:
_{ET A + D A -T A '} = ST B + D B -T B' (3)
It becomes. Here, T _A ′ and T _B ′ indicate the values of T _A and T _{B at} a certain time. Assuming that the time code measured by the video receiver 20 at this time is OT _A ′ and OT _B ′, according to Equation (1), Equation (2), and Equation (3),
_{ST B = ET A + OT B} '-OT A' (4)
Holds.

In the transmission path coupling device 10,
_{ET A '= ET A + D} A -T A', ST B '= ST B + D B -T B'
When, by the video transmission fadeout portion which will be described later in the video transmitting apparatus A, the bit rate of the video signal A is remained as _'from time ET _A' time ET A in FIG. 4 to + FT, described later in the video transmitting apparatus B the video transmitting fade-section of the bit rate of the video signal B changes as from time ST _B in FIG. 4 to time ST B ₊ FT. This cross-fading process can be performed by consuming the buffer of the video receiving device 20 at the time of video transmission fading out, and the transition of the buffer amount in the video transmitting devices A and B and the video receiving device 20 at this time is as follows. As shown in FIG.

As a result, the transmission delays D _A and D _B shown in FIG. 3 fluctuate due to network jitter and the like, so that when the total bit rate of the video signal A and the video signal B at the instant of video switching varies, The ratio can be suppressed and the occurrence of instantaneous congestion as shown in FIG. 6 can be prevented.

  According to the principle of the present invention described with reference to FIGS. 1 to 6, the temporal granularity of the switching control depends on the granularity of the time code and the granularity of the processing unit in the video transmission / reception apparatus. For example, when the time code granularity is in units of one frame of video and the transmission / measurement of the time code and the start / stop processing of video transmission are performed in units of one frame of video in the video transmission / reception apparatus, the accuracy is less than the time of one video frame Switching control cannot be performed. This means that the time at which the stream is switched is at most around one frame time of video, and it is unavoidable that overlap occurs at the time of switching. In order to prevent network congestion due to this overlap, crossfading processing is performed according to the above-described principle.

  The present invention further performs switching control for one frame or less of video, that is, for each video line, in order to prevent stream overlap itself. However, if the granularity of the time code sent from the video transmission apparatus is set on a line basis or the granularity of processing on the video transmission / reception apparatus is set on a line basis, the network load and the processing load increase, and the cost of the system increases. Therefore, the present invention prevents an increase in the cost of the system and performs switching control in line units. Further, in a long-time stream transmission, by adjusting the buffer amount at the video switching timing, it is possible to suppress the buffer overflow and the buffer underflow caused by the clock difference between the transmission device and the reception device.

In order to realize line-by-line switching control, in the present invention, the time code indicating the position of the video in the time axis direction is a frame number in units of one video screen, and a line in units of one scanning line as a finer unit. Contains a number. If the time code is T, the frame number is F, and the line number is L, T = F. L. If the number of video lines constituting one video frame is L _MAX , 0 ≦ L ≦ L _MAX −1. When L = L _MAX −1, when L is increased by 1, F is increased by 1 and L becomes 0. . Ta = Fa. La, Tb = Fb. For Lb, addition and subtraction are performed as follows:
Ta + Tb
= (Fa + Fb). (La + Lb)
... When La + Lb <L _MAX = (Fa + Fb + 1). (La + Lb-L _MAX )
... When La + Lb ≧ L _MAX (5)
Ta-Tb
= (Fa-Fb). (La-Lb)
... When La ≧ Lb = (Fa−Fb−1). (La-Lb + L _MAX )
... When La <Lb (6)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 7 shows the configuration of the transmission / reception system according to the first embodiment of the present invention.

  The transmission / reception system shown in the figure includes video transmission devices 600A and 600B and a video reception device 700.

  The video transmission apparatus 600 includes a video input unit 610, a video transmission unit 620, a time code generation unit 630, a time code transmission unit 640, a buffer 650, a video fade-out unit 660, a video transmission fade-in unit 670, and a buffer control unit 680. The

  The video reception device 700 includes a video reception unit 710, a video output unit 720, a time code measurement unit 730, a video transmission stop time code generation unit 740, a video transmission start time code 750, and a buffer 760.

  The transmission paths between the plurality of video transmission apparatuses 600A and 600B and the video reception apparatus 700 are combined into one in the middle path coupling apparatus 10 as in FIG. The transmission path is a line occupation type or packet transmission type path. When the transmission path is a line occupation type path, the path coupling device 10 is a line switching unit or a signal addition unit. When the transmission path is a packet transmission type path, the path coupling unit is a packet switching unit.

  FIG. 8 is a sequence chart of the operation in the first embodiment of the present invention.

In step S101, the video signal is input to the video input units 610A and 610B in the video transmission device 100A that is the video switching source and the video transmission device 100B that is the video switching destination. At the same time, time codes T _A and T _B associated with the input video signal are generated in time code generation units 630A and 630B, respectively. The time code is generated as follows. In the video transmission device 600A as the video switching source and the video transmission device 600B as the video switching destination, video signals are input to the video input units 610A and 610B. At the same time, time codes T _A and T _B associated with the input video signal are generated in time code generation units 630A and 630B, respectively. The time code is generated based on the clock of the input video signal, or when the time code is given to the input video signal, the time code may be used as it is as the generation time code. In the SMPTE time code or the like that is generally used, the minimum unit of time information is a video I frame. However, a time code in a finer unit may be generated using a horizontal synchronization signal of video. That is, the time code may include a frame number in units of one video screen and a line number in units of one scanning line as a finer unit.

  Next, in step S102, video transmission apparatus 600A transmits the input video signal from video signal transmission unit 620A via the transmission path. At this time, the video transmission device 600A transmits the video for a predetermined time BT from the video signal transmission unit 620A while buffering the video in the buffer 650A. Note that buffering may be omitted if video switching from another video transmission device to the video transmission device 600A has not been performed before this.

  In step S103, the video reception device 700 receives the video transmitted from the video transmission device 600A by the video reception unit 710, and outputs the video from the video output unit 720 while buffering the video of at least a predetermined time BT in the buffer 760. I do.

In step S104, the time code measuring unit 730 of the video receiving device 700 receives and measures the time codes from both the video transmitting devices 600A and 600B, and the measured time code OT _A and the video from the video transmitting device 600A. The measured time code OT _B is obtained from the transmission device 600B.

In step S105, the video transmission stop time code generator 740 generates the ET _A, is transmitted to the video transmission apparatus 600A. ET _A may be a value designated in advance by the user, or may be generated based on OT _A when a video switching request is received from the user. However, in this case, when the ET _A video transmission start time code ST _B reaches the video transmitter 600A and a video transmission device 600B, you must already have to generate ET _A so that time is not past . Therefore, to set a sufficiently long time compared to previously transmission delay time, or to generate an ET _A adds that value to OT _A, both from the video receiving device 700 the video transmission apparatus 600A, the transmission delay time to the 600B measured, the longer transmission delay time of adding the OT _a, it is desirable to generate ET _a. The transmission delay time is measured using ICMP (Internet Control Message Protocol) Echo Message, Echo Reply Message, and the like. Further, the value of the crossfade time FT may be generated and transmitted to the video transmission device 600A.

The video transmission start time code generation unit 750 generates ST _B as follows using the time codes OT _A and OT _B measured with the accuracy of the number of video lines:
_{ST B = ET A + (OT} B - (OT A -OL A)) (7)
Here, OL _A is the value of the line number portion of OT _A. The video transmission start time code generation unit 750 transmits the generated ST _B to the video transmission device 600B. At this time, similarly, a value of the crossfade time FT may be generated and transmitted to the video transmission device 600B. In generating the crossfade time FT, DT _B may be measured a plurality of times at different times in advance, and the value of FT may be increased according to the standard deviation of the statistical value.

In step S106, the buffer control unit 680A of the video transmission apparatus 600A receives the ET _A from the video transmission stop time code generator 740 of the video receiver _apparatus, and at the same time the T A = ET _A, to stop buffering buffer 650A is controlled and a transmission stop process is performed. When the fade-out process is not performed, the video signal in the transmission buffer 650A is transmitted at a normal bit rate, and the video transmission stops when the transmission buffer 650A becomes empty. In the video transmission fade-out unit 660A of the video transmission device 600A, when performing the fade-out process in the n frame time, the fade-out process is started when the remaining data amount in the buffer becomes n / 2. In addition, the number of lines of the ET _A, namely EL _A is always zero. In the video transmission fade-out, the transmission bit rate is decreased stepwise so that the transmission of the video existing in the buffer 650A at that time is completed simultaneously with the elapse of the crossfade time n frames, or the normal bit rate is exceeded. The video transmission is performed while maintaining a low and constant bit rate, and then the video transmission is stopped.

In step S107, in parallel with the step S106 described above, the buffer control unit of the video transmission apparatus 600B receives the ST _B from the video transmission start time code generator 750 of the video receiver 700, ST _B timecode _{T B} The buffer 650B is controlled so as to start buffering only for the time of the line number SL _B of ST _{B at} the same time as the frame number SF _{B of} ST _B. After time of SL _B, it performs the transmission start processing from the head data in the buffer. In the video transmission fade-in unit 670B of the video transmission device 600B, when the fade-in process is performed in the n frame time, it starts at this point. In video transmission fade-in, the transmission bit rate is increased stepwise so that transmission of video for n / 2 frame time is completed as soon as n frame time has elapsed, or a fixed amount lower than the normal bit rate. This is done by starting video transmission while maintaining the bit rate. At this time, the fade-in process is completed at the same time as the buffering of the video for n / 2 frame time is completed.

  This enables video switching at an optimal switching timing with video line accuracy without increasing the load on the video transmission device.

  In step S108, the video reception device 700 performs buffering of the video from the video transmission device 600B until the reproduction of the video from the video transmission device 600A is completed.

  In step S109, the video receiving device 700 starts playback of the video from the video transmitting device 600B at the same time that the buffered video transmitting device 600A runs out of video and the playback ends.

[Second Embodiment]
FIG. 9 shows a configuration of a transmission / reception system according to the second embodiment of the present invention. FIG. 9 shows a configuration in which a buffer monitoring unit 770 is added to the video reception device 700 of FIG.

  FIG. 10 is a sequence chart of the operation in the third embodiment of the present invention. Steps S201 to S204 in FIG. 10 are the same as steps S101 to S104 in FIG.

Step S205 differs from step S105 described above in the following points. The buffer monitoring unit 770 sets a target value, an upper limit threshold value, and a lower limit threshold value for the buffer amount of the buffer 760, and receives a stream in the video reception device 700 and is in a steady state that is not a video switching period. The excess line number L _ov whose buffer amount exceeds the upper limit threshold and exceeds the target value is monitored. The video transmission stop time code generation unit 740 obtains the excess line number L _ov from the buffer monitoring unit 770 and obtains ST _B as follows:
_{ST B = ET A + (OT} B - (OT A -OL A)) + L ov (8)
Conversely, when the buffer amount is lower than the lower limit threshold and is less than the target value by L _ud lines, the number of short lines L _ud below the target value is monitored. The video transmission stop time code generation unit 740 obtains the excess line number L _ud from the buffer monitoring unit 770 and obtains ST _B as follows:
ST _B = ET _A + (OT _B − (OT _A −OL _A )) − L _ud (9)
Due to the deviation between the video source clock on the video transmission device 600 side and the system internal clock of the video reception device 700, the buffer amount at the client may gradually change during long-time streaming, which may cause buffer overflow or buffer underflow. There is. On the other hand, according to the above-described method, it is possible to adjust the buffer amount of the video receiving apparatus 700 within a specified range at the time of video switching, and it is possible to avoid the occurrence of buffer overflow and buffer underflow.

  Steps S206 to S209 are the same as steps S106 to S109 in FIG.

[Third Embodiment]
FIG. 11 shows the configuration of a video transmission / reception system according to the third embodiment of the present invention.

  The video transmission / reception system shown in the figure includes video transmission devices 600A and 600B, a video reception device 400, and a control device 500. The control device may be implemented by a personal computer, workstation, dedicated computer, or any computer capable of performing the functions described above.

  In the present embodiment, the video transmission stop time code generation unit 740 and the video transmission start time code generation unit 750 of the video reception device 700 in the first embodiment are moved to the control device 500, and a measurement time code is newly added. Is configured to include a measurement time code transmission unit that transmits the information to the control device 500.

  The video reception device 400 includes a video reception unit 410, a video output unit 420, a time code measurement unit 430, a measurement time code transmission unit 440, and a buffer 460.

  The control device 500 includes a video transmission stop time code 510 and a video transmission start time code generation unit 520. These configurations have the same functions as the video transmission stop time code generation unit 740 and the video transmission start time code generation unit 750 of the video reception device 700 according to the first embodiment.

  FIG. 12 is an operation sequence chart according to the third embodiment of the present invention. Steps S301 to S304 in FIG. 10 are the same as steps S101 to S104 in FIG. 8, and the description is omitted because the video reception device 700 may be replaced with the video reception device 400.

In step S305, the calculated measurement time codes OT _A and OT _B are transmitted from the measurement time code transmission unit 440 to the control device 500.

In step S306, video transmission stop time code generation unit 510 of control device 500 receives OT _A , and video transmission start time code generation unit 520 receives OT _B.

In step S307, the video transmission stop time code generation unit 510, in the same manner as step S105 of FIG. 8 to generate a video transmission stop time code ET _A, is transmitted to the video transmission apparatus 600A. The video transmission start time code generation unit 520 also transmits the generated ST _B to the video transmission device 600B by the same method as step S105 in FIG.

  Steps S308 to S311 are the same as steps S106 to S109 in FIG.

[Fourth Embodiment]
FIG. 13 shows the configuration of a video transmission / reception system according to the fourth embodiment of the present invention. FIG. 13 shows a configuration in which a buffer monitoring unit 470 and a line number transmission unit 480 are added to the video reception device 400 of FIG.

  FIG. 14 is a sequence chart of operations in the fourth embodiment of the present invention. Steps S401 to S404 in FIG. 14 are the same as steps S201 to S204 in FIG.

In step S405, the buffer monitoring unit 470 sets a target value, an upper limit threshold value, and a lower limit threshold value for the buffer amount of the buffer 460, and receives a stream in the video reception device 400 in a steady state that is not a video switching period. The excess line number L _{ov in} which the buffer amount of the receiving device 400 exceeds the upper threshold and exceeds the target value is monitored. On the other hand, when the buffer amount is lower than the lower limit threshold value and less than the target value by the L _ud line, the buffer monitoring unit 470 monitors the number L _ud of insufficient lines that are below the target value.

In step S406, the calculated measurement time codes OT _A and OT _B are transmitted from the measurement time code transmission unit 440 to the control device 500. Also, L _ov and L _ud are transmitted from the line number transmission means 480 to the video transmission stop time code generation unit 510.

In step S407, the video transmission stop time code generation unit 510 of the control device 500 receives OT _A and L _ov or L _ud , and the video transmission start time code generation unit 520 receives OT _B. When the video transmission stop time code generation unit 510 obtains the excess line number L _ov from the line number transmission means 480, it obtains ST _B as follows:
_{ST B = ET A + (OT} B - (OT A -OL A)) + L ov (8)
When the video transmission stop time code generation unit 340 obtains the excess line number L _ud from the line number transmission means 480, the ST _B is obtained as follows:
ST _B = ET _A + (OT _B − (OT _A −OL _A )) − L _ud (9)
Steps S408 to S411 are the same as steps S206 to S209 in FIG.

Referring to FIGS. 15 to 18, the number of lines constituting one frame L _MAX = 1125, the line number L satisfies 0 ≦ L ≦ 1124, and the measurement time code calculation period dRT in the video receiving apparatus is one frame. A case will be described.

FIG. 15 is a diagram for explaining the relationship between the transmission delay and each time code when switching from the video transmission device A to the video transmission device B. In the control device, to determine the video transmission stop timing ET _A by the user of the request to the video transmission apparatus A. When performing video switching in response to switching operation by the user, the OT _A when the user performs the switching operation, the value obtained by adding the larger of round trip transmission delay as a margin time of switching target as ET _A Transmit to the video transmission device A. Since ET _A must be in the range of frames, OT _A performs calculation by rounding up to the frame. The round trip transmission delay is the sum of the delay time from each video transmission device to the video reception device and the delay time from the control device to each video transmission device. In Figure 15, for round trip transmission delay _{d A} of the video transmission apparatus A is less than 5 frames, _ET A = 109 by the value of _{d A} was added to the OT _A switching operation time of the user, rounded up to the frame. Get 0.

Next, the video stop timing ST _B is obtained using the above equation (7). That means
_{ST B = ET A + (OT} B - (OT A -OL A))
= 109.0 + (86.175- (103.1025-0.1025))
= 92.175
The the obtained ET _A to the video transmission device A, the ST _B in the video transmission apparatus B, and transmitted from the respective control device.

FIG. 16 is a diagram illustrating transmission stop processing in the video transmission apparatus A when the cross-fade period is 2 frames. When the internal time code T _A server A is equal to the ET _A, since the buffer amount at this time is one frame and the 1025 line, until the buffer amount becomes 1 frame is half of the cross-fade period That is, transmission is performed at a normal bit rate for 1025 lines. At this time, the actually transmitted stream is video data with a time code of 107.100 to 108.0. Subsequently, fade-out processing for transmitting one frame of video data in two frame times is performed. As a result, the transmission of the stream A is stopped after the video frame having the time code 108.0.

FIG. 17 is a diagram for explaining a transmission start process in the video transmission apparatus B. When the internal time code T frame number _B of the video transmission apparatus B which becomes equal to the frame number, i.e. 92 ST _B, starts buffering of the video frame of the time code 92.0. Then T line number is the line number of the ST _B of _B, ie when becomes equal to 175, it performs the fade-in process of transmitting the image data of one frame in two frame times. Thereby, after completion of the fade-in process, the buffer amount of the video transmission apparatus B becomes 1 frame and 175 lines.

FIG. 18 is a diagram illustrating changes in the bit rate of each video transmission device on the same time axis. Although transmission of the stream B is started one frame later than the stream A, since d _A1 = 2 and d _B1 = 1 from FIG. 15, the stream B arrives at the video receiving apparatus one frame earlier than the stream A. It can be seen that in the video receiver, the two streams are switched at exactly the same timing.

Incidentally, such switching by playback list, when the ET _A is designated in advance by the user, _{OT A} is ET _A - before reaching the margin time, transmits the ET _A and ST _B in the video transmission apparatus.

When the cross-fade period is 2 frames, the buffer amount of the video receiving apparatus needs at least 1 frame. The target buffer amount is 1.100, the lower threshold is 1.0, and the upper threshold is 1.200. When the buffer amount of the video reception device is 1.300 at the time of switching in FIG. 15, the upper limit threshold is exceeded and there are 200 lines more than the target value, so the above equation (8) is used,
_{ST B = ET A + (OT} B - (OT A -OL A)) + 0.200
= 92.400
Is required. As a result, the start of the stream B is delayed by 200 lines, so that the buffer amount of the video receiving apparatus is reduced by 200 lines to the target value of 1.100.

On the contrary, when the buffer amount of the video receiving device is 0.1000, since it is lower than the lower limit value and 225 lines less than the target value, the above equation (9) is used.
ST _B = ET _A + (OT _B − (OT _A −OL _A )) − 0.225
= 91.1100
Is required. As a result, the start of the stream B is advanced by 225 lines, so that the buffer amount of the video receiving apparatus increases by 225 lines to reach the target value of 1.100.

  Note that when the start of the stream B is advanced, the total bit rate during the cross-fade period is increased, and therefore, it is necessary to perform within a range not exceeding the bandwidth of the transmission path.

  The functions of the video transmission device and the video reception device described above can be constructed as a program, installed in a computer used as these devices, executed, or distributed via a network.

  Further, the constructed program can be stored in a portable storage medium such as a hard disk, a flexible disk, or a CD-ROM, and can be installed or distributed in a computer.

  The present invention is not limited to the above-described embodiment, and various modifications and applications can be made within the scope of the claims.

  As described above, according to the present invention, the lime code measuring means receives the time code from the video transmitting apparatus in parallel with the video stream receiving process in the video receiving means, and receives the time code and the time code. The measurement time code can be calculated based on the time code counted inside the video receiver at the time. Thereby, the time granularity of the time code can be shortened to the video line unit, and as a result, the video switching time can be shortened.

  The present invention is applicable to a video transmission / reception system that relays and transmits video.

It is a principle block diagram of this invention. It is a figure for demonstrating the principle of this invention. It is a figure for demonstrating the operation principle of the video transmission start time code production | generation process of this invention. It is a figure which shows the bit rate of the video signal of the video transmission apparatus of this invention. It is a figure which shows transition of the buffer amount of the video transmission apparatus and video reception apparatus of this invention. It is a figure which shows the fluctuation | variation of the total bit rate of this invention. It is a block diagram of the video transmission / reception system in the 1st Embodiment of this invention. It is a sequence chart of the operation | movement in the 1st Embodiment of this invention. It is a block diagram of the video transmission / reception system in the 2nd Embodiment of this invention. It is a sequence chart of operation in a 2nd embodiment of the present invention. It is a block diagram of the video transmission / reception system in the 3rd Embodiment of this invention. It is a sequence chart of operation in a 3rd embodiment of the present invention. It is a block diagram of the video transmission / reception system in the 4th Embodiment of this invention. It is a sequence chart of operation in a 4th embodiment of the present invention. It is a figure explaining the relationship between the transmission delay at the time of switching from 100 A of video transmission apparatuses to the video transmission apparatus 100B, and each time code. It is a figure explaining the transmission stop process in the video transmission apparatus A in case a cross fade period is 2 frames. It is a figure explaining the transmission start process in the video transmission apparatus. It is a figure explaining the change of the bit rate of each video transmission device on the same time axis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Video transmission device 110 Video input part 120 Video transmission part 130 Time code production | generation means 140 Time code transmission means 150 Video transmission stop means 160 Video transmission start means 300 Video reception apparatus 310 Video reception means 320 Video output means 330 Time code measurement means 340 Video transmission stop time code generation means 350 Video transmission start time code generation means 400 Video reception device 410 Video reception section 420 Video output section 430 Time code measurement section 440 Measurement time code transmission section 460 Buffer 470 Buffer monitoring section 480 Line number transmission section 500 Control device 510 Video transmission stop time code generation unit 520 Video transmission start time code generation unit 600 Video transmission device 610 Video input unit 620 Video transmission unit 630 Time code generation unit 640 Code transmission unit 650 Buffer 660 Video transmission fade-out unit 670 Video transmission fade-in unit 680 Buffer control unit 700 Video reception device 710 Video reception unit 720 Video output unit 730 Time code measurement unit 740 Video transmission stop time code generation unit 750 Video transmission start time Code generator 760 buffer

Claims (6)

A video transmission / reception system in which a video reception device switches received video from one video transmission device to another video transmission device among a plurality of video transmission devices,
The video receiver is
Time code measuring means for measuring the time code received from the video transmission device with the accuracy of the number of video lines;
Based on the measured time code, the video transmission stop time code generating means for generating and transmitting the video transmission stop time code ET to the current video receiving destination video transmitting device, or the measured time code A video transmission start time code generating means for generating and transmitting a video transmission start time code ST to the video transmission device of the video switching destination,
The video transmission device includes:
Time code generation means for generating a time code T;
A transmission buffer for holding a video signal for a predetermined time;
When the ET is received, the buffer is controlled to stop buffering when T = ET, or when the ST is received and the frame numbers of T and ST are equal, the buffer is provided for the time corresponding to the ST line number SL. A buffer control unit for controlling the transmission buffer to start a ring;
A video transmission / reception system comprising: video transmission means for starting transmission from the video signal at the head of the transmission buffer to the video reception device after elapse of the SL time. The video receiver is
A reception buffer that holds video for a predetermined time with respect to the input video;
A target value, an upper limit threshold value, and a lower limit threshold value are set for the amount of video signal in the reception buffer, and the number of excess lines exceeds the upper limit threshold value and exceeds the target value, or the amount is lower than the lower limit threshold value. A buffer monitoring unit that monitors the number of insufficient lines below a target value, and transmits the number of excess lines or the number of insufficient lines to the video transmission start time code generation unit,
The video transmission start time code generation unit obtains the ST based on the number of excess lines or the number of insufficient lines, the ET, and the measurement time code.
The video transmission / reception system according to claim 1. The video transmission device includes:
When the video signal in the transmission buffer becomes half of the predetermined crossfade time FT, the transmission bit rate is decreased stepwise or the normal bit so that the video signal in the transmission buffer is completed simultaneously with the FT. Video transmission fade-out means for performing video transmission with a constant bit rate lower than the rate, and then stopping video transmission;
After the SL time, the transmission bit rate is increased stepwise or a certain amount of bit rate lower than the normal bit rate so that video transmission for half the time of the FT is completed simultaneously with the FT. 2. The video transmission / reception system according to claim 1, further comprising video transmission fade-in means for starting video transmission while maintaining and buffering video signals corresponding to half the time of the FT. A method of controlling a transmission buffer of the video transmission device in a video transmission / reception system in which the video reception device switches received video from one video transmission device to another video transmission device among a plurality of video transmission devices,
The video receiver is
Measuring the time code received from the video transmission device with the accuracy of the number of video lines;
Based on the measured time code, a step of generating and transmitting a video transmission stop time code ET to the current video receiving destination video transmitting device, or based on the measured time code, a video switching destination Generating and transmitting a video transmission start time code ST to the video transmission device; and
The video transmission device includes:
Generating a time code T;
Holding a video signal for a predetermined time;
When the ET is received, the buffer is controlled to stop buffering when T = ET, or when the ST is received and the frame numbers of T and ST are equal, the buffer is provided for the time corresponding to the ST line number SL. Controlling the transmit buffer to initiate a ring;
And a step of starting transmission from the video signal at the head of the transmission buffer to the video reception device after the SL time has elapsed. The video receiver is
Holding a video for a predetermined time with respect to the input video;
A target value, an upper limit threshold value, and a lower limit threshold value are set for the amount of video signal in the reception buffer, and the number of excess lines exceeds the upper limit threshold value and exceeds the target value, or the amount is lower than the lower limit threshold value. Monitoring the number of insufficient lines below a target value, and transmitting the excess line number or the insufficient line number to the video transmission start time code generation unit;
5. The transmission buffer control method according to claim 4, wherein the ST is obtained based on the number of excess lines or the number of insufficient lines, the ET, and the measurement time code. The video transmission device includes:
When the video signal in the transmission buffer becomes half of the predetermined crossfade time FT, the transmission bit rate is decreased stepwise or the normal bit so that the video signal in the transmission buffer is completed simultaneously with the FT. Performing video transmission while maintaining a certain amount of bit rate lower than the rate, and then stopping video transmission;
After the SL time, the transmission bit rate is increased stepwise or a certain amount of bit rate lower than the normal bit rate so that video transmission for half the time of the FT is completed simultaneously with the FT. 5. The transmission buffer control method according to claim 4, further comprising: starting video transmission while maintaining and buffering video signals corresponding to half the time of the FT.

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