JP3191439B2 - Coded image signal switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coded picture signal switching apparatus for switching compressed digital coded picture signals of a plurality of channels.

[0002]

2. Description of the Related Art Various methods for compressing and encoding an image signal have been proposed. One method of compressing and encoding the image signal is, for example, an inter-frame encoding method.

In the case of this inter-frame coding method, one intra-frame coded image (intra frame, refresh frame) is usually inserted in several frames in order to prevent propagation of an error due to coding. That is, one intra frame is inserted at regular intervals.

Here, as a specific example of the inter-frame encoding method, for example, a so-called MPEG (Moving Pictu
A standardization proposal by the Re Experts Group) specifies a high-efficiency encoding method for image signals for so-called digital storage media. Here, the storage media targeted by this method are those having a continuous transfer speed of about 1.5 Mbit / sec or less, such as a so-called CD (compact disk), DAT (digital audio tape recorder), and hard disk. is there. It is not only connected directly to the decoder, but also to the computer bus, LAN (local area network),
It is assumed that connection will be made via transmission media such as telecommunications, satellite transmission, etc. In addition to normal-order playback, special functions such as random access, high-speed playback, and reverse-order playback will be considered. Have been.

[0005] The principle of the high-efficiency encoding method for an image signal by the above-mentioned MPEG is as follows.

That is, in this high-efficiency coding method, first, the redundancy between images is reduced by taking a difference between images, and thereafter, a so-called discrete cosine transform (DCT) process and a variable length code are used. To reduce the redundancy in the space axis direction.

First, the redundancy in the time axis direction will be described below.

Generally, in a continuous moving image, an image preceding and succeeding in time is similar to an image of interest (ie, an image at a certain time). Therefore, for example, as shown in FIG. 4, if a difference between an image to be coded and a temporally forward image is obtained and the difference is transmitted, the redundancy in the time axis direction can be reduced. It is possible to reduce the amount of information to be transmitted. The image encoded in this manner is called a forward predictive encoded image (Predictive-coded picture, P picture or P frame) described later. Similarly, the difference between the image to be coded and the interpolated image formed from the front or the rear or the front and the rear in time is calculated, and the difference between the small values is transmitted. Then, it is possible to reduce the amount of information to be transmitted by reducing the redundancy in the time axis direction. An image encoded in this way is a bidirectional predictive encoded image (Bidirectio
nallyPredictive-coded picture, B picture or B
Frame). In FIG. 4, an image indicated by I in the figure is an intra-coded image (Intra-coded picture: I-picture or I-picture) described later.
The image shown by P in the figure shows the P picture, and the image shown by B in the figure shows the B picture.

In order to generate each predicted image, so-called motion compensation is performed. That is, according to this motion compensation, a block of, for example, 16 × 16 pixels (hereinafter referred to as a macroblock) composed of, for example, a unit block of 8 × 8 pixels is created, and the block is located near the position of the macroblock in the previous image. By searching for a place with a small difference and calculating the difference with the searched macroblock, data to be sent can be reduced. Actually, for example, in the P picture (forward prediction coded image), the difference between the prediction image after motion compensation and the difference between the prediction image after motion compensation and Those with a small amount are selected and coded in macroblock units of 16 × 16 pixels.

However, in the case described above, for example, a large amount of data must be sent for a portion (image) that comes out after the object has moved. Therefore, for example, in the above B picture (bidirectional predictive coded image), the already decoded temporally forward or backward image after motion compensation and the interpolated image formed by adding both of them will be coded from now on. And the image which does not take the difference, that is, the image having the smallest data amount among the four images to be encoded from now.

Next, the redundancy in the space axis direction will be described below.

The difference between the image data is not transmitted as it is, but is subjected to discrete cosine transform (DCT) for each unit block of 8 × 8 pixels. The DCT expresses an image not by a pixel level but by how many frequency components of a cosine function are included. For example, by a two-dimensional DCT, data of a unit block of 8 × 8 pixels is two-dimensional. It is converted into a coefficient block of an 8 × 8 cosine function component by DCT. For example, an image signal of a natural image taken by a television camera is often a smooth signal. In this case, the DCT is applied to the image signal.
By performing the processing, the data amount can be efficiently reduced.

That is, for example, in the case of a smooth signal such as the above-described image signal of a natural image, by applying the DCT, a large value is concentrated around a certain coefficient. When these coefficients are quantized, most of the 8 × 8 coefficient blocks become 0, and only large coefficients remain. Therefore, when transmitting the data of the 8 × 8 coefficient block, a set of non-zero coefficients and a so-called zero run indicating how much 0 continues before the coefficient in the order of so-called zigzag scanning. By transmitting the so-called Huffman code, the amount of transmission can be reduced. On the decoder side, an image is reconstructed in the reverse procedure.

FIG. 5 shows the structure of data handled by the above-described high-efficiency coding method. That is, the data structure shown in FIG. 5 includes, in order from the bottom, a block layer, a macroblock layer, a slice layer, a picture layer, a group of picture (GOP) group, and a video sequence layer. . Hereinafter, description will be made in order from the lower layer in FIG.

First, in the above-mentioned block layer, a block of the block layer is composed of 8 × 8 pixels (8 lines × 8 pixels) having adjacent luminance or color difference. The DCT (discrete cosine transform) described above is applied to each unit block.

In the macroblock layer, the macroblocks in the macroblock layer include four luminance blocks (luminance unit blocks) Y0,
Y1, Y2, Y3 and a color difference block (color difference unit block) C at the same position as the luminance block on the image.
r and Cb are composed of a total of six blocks. The order of transmission of these blocks is Y0, Y1, Y2, Y3, C
r, then Cb. Here, in the encoding method, what is used for a predicted image (a reference image for obtaining a difference)
Alternatively, whether or not the difference need not be transmitted is determined in units of this macroblock.

The above-mentioned slice layer is composed of one or a plurality of macro blocks connected in the scanning order of the image. At the beginning of this slice (header), the difference between the motion vector and the DC (direct current) component in the image is reset, and the first macroblock has data indicating the position in the image, so that an error occurs. It is designed to allow you to return if something happens. Therefore, the length of the slice and the starting position are arbitrary, and can be changed according to the error state of the transmission path.

In the picture layer, a picture, that is, each picture is composed of at least one or a plurality of the slices. Then, each of the above-described intra-coded images (I
Picture or I frame), forward predictive coded picture (P picture or P frame), bidirectional predictive coded picture (B picture or B frame), DC intra coded picture (DC coded (D) picture) Classified into images.

Here, in the above-mentioned intra-coded image (I picture), at the time of coding, only closed information in one image is used. Therefore, in other words, when decoding, an image can be reconstructed using only the information of the I picture itself. Actually, encoding is performed by DCT processing without taking a difference. This encoding method is generally inefficient, but if it is included everywhere, random access and high-speed reproduction can be performed.

In the forward predictive coded picture (P picture), an I picture or P picture which is located temporally earlier in the input and has already been decoded is used as a predicted picture (picture serving as a reference for obtaining a difference). I do. In practice, the more efficient one of coding the difference from the motion-compensated predicted image and coding the difference without taking the difference (intra code) is selected in units of the macroblock.

The above bidirectional prediction coded image (B picture)
Uses three types of predicted images, i.e., an I-picture or a P-picture that is located earlier in time and has already been decoded, and an interpolated image created from both of them. This allows
The most efficient one of the above three types of difference-encoded differential coding and intra-coding can be selected in macroblock units.

The DC intra-coded image is an intra-coded image composed only of DCT DC coefficients.
It cannot exist in the same sequence as the other three images.

The group of pictures (GOP) layer includes one or more I-pictures and zero or more non-I-pictures.
And a picture. Here, the input order to the encoder is, for example, 1I, 2B, 3B, 4P * 5B, 6
B, 7I, 8B, 9B, 10I, 11B, 12B, 13
P, 14B, 15B, 16P * 17B, 18B, 19
When I, 20B, 21B, and 22P are used, the output of the encoder, that is, the input of the decoder is, for example, 1I, 4
P, 2B, 3B * 7I, 5B, 6B, 10I, 8B, 9
B, 13P, 11B, 12B, 16P, 14B, 15B
* 19I, 17B, 18B, 22P, 20B, 21B. The reason why the rearrangement of the order is performed in the encoder is, for example, in the case of encoding or decoding the B picture, the I picture or the P picture which is a temporally backward prediction image. This is because the picture must be coded first. Here, the interval between the I pictures (for example, 9) and the interval between I or B pictures (for example, 3) are free. Also, I picture or P
The picture interval may vary within the group of pictures layer. The breaks in the group of picture layers are indicated by *. In addition, I indicates an I picture, P indicates a P picture, and B indicates a B picture.

The video sequence layer has an image size,
It is composed of one or more group of picture layers having the same image rate.

As described above, when transmitting a moving image standardized by the above-described MPEG high efficiency coding method, an image obtained by compressing one image in a picture is transmitted first, and then this image is transmitted. The difference from the motion-compensated image is transmitted.

[0026]

By the way, the future digital television broadcasting may be performed with a compressed and coded image signal by the above-mentioned inter-frame coding method which can be expected to have a low bit rate and a large number of channels. There is. Therefore, for example, in a broadcasting station, a cable television station, a local distribution station, or the like, when broadcasting a digitally coded image signal adopting the inter-frame coding method, for example, a switching operation of a plurality of channels ( There is a possibility that an encoded program sent from a program supplier in each region is switched, or a unique local program or a so-called CM is inserted.

However, in the above-mentioned inter-frame coding method, as described above, since the other frames except the intra-frame inserted at a certain interval depend on the previous data in time, However, if switching is performed at an arbitrary timing when switching signal sequences of a plurality of channels, there is a problem that signals before and after switching are difficult to be connected well (signals cannot be connected without failure).

Although switching of a digitally coded image signal to which inter-frame coding is applied is currently discussed as a future necessity, there is no device disclosed.

The present invention has been made in view of such circumstances, and can appropriately switch digitally encoded image signals of a plurality of channels to which interframe encoding is applied (connecting signals without failure). It is an object of the present invention to provide a coded image signal switching device.

[0030]

SUMMARY OF THE INVENTION An encoded image signal switching apparatus according to the present invention has been proposed to achieve the above-mentioned object, and has a plurality of channels of digital codes compressed and encoded by inter-frame encoding. A coded image signal switching device for switching coded image signals, a memory means provided for each channel and for writing / reading the digital coded image signal for at least a period of an interval between intra-frames; And control means for controlling the memory means corresponding to the second channel so as to read from the intra frame when switching from the digitally coded image signal to the digitally coded image signal of the second channel. It is made.

Further, the coded image signal switching device of the present invention also has frame completion information extracting means for extracting information indicating the completion of a frame from the digitally coded image signal. When switching from the signal to the digital coded image signal of the second channel, the control means controls the conversion of the digital coded image signal of the first channel based on the information from the frame completion information extracting means. The memory means corresponding to the first channel is controlled so that reading is performed until the frame is completed.

Here, when the digitally coded image signal of each channel is a satellite transmission signal, a transmission signal from an optical fiber, or a transmission signal from a randomly accessible recording medium, the memory means is capable of performing the random access. It should be provided only on the channels excluding the channels corresponding to the transmission signals from the various recording media. Therefore, when switching to the channel of the transmission signal from the random accessible recording medium, the control means controls the reproduction of the random accessible recording medium so as to read out from the intra frame.

[0033]

In other words, the coded image signal switching device of the present invention is a coded image signal switching device for switching digitally coded image signals of a plurality of channels, the information of which is compressed by inter-frame coding. When switching from the digitally encoded image signal of the first channel to the digitally encoded image signal of the second channel,
The end of the appropriate video frame of the digitally encoded image signal of the first channel is searched for and cut off, and the digitally encoded image signal of the second channel is previously stored in memory means (F
This is to search for the immediately preceding refresh frame (intra frame) from the image signal stored in the IFO memory and connect it.

[0035]

According to the present invention, in the case of inter-frame coding, normal decoding can be performed later by using intra-frames. Therefore, when switching from the first channel to the second channel, The memory means is controlled so as to read from the intraframe of the digitally encoded image signal of the second channel. As a result, the switched digital coded image signal of the second channel becomes a signal after the intra frame, and therefore, the switched digital coded image signal of the second channel becomes a normal image after the intra frame. It can be decoded as a signal.

Further, according to the present invention, when switching from the first channel to the second channel, the first channel
The reading from the memory means corresponding to the first channel is continued until the frame of the digital coded image signal of the first channel is completed, and immediately after the frame of the digital coded image signal of the first channel is completed, 2
Is switched to the digitally coded image signal of the first channel.
Can be normally decoded later.

Further, of the digitally encoded image signal systems of each channel, the transmission signal system from a randomly accessible recording medium is controlled by controlling the reproduction of the randomly accessible recording medium such that it is read from an intra frame. Thus, no memory means is required.

That is, according to the present invention, since the digitally encoded image signal of each channel is switched without decoding, error correction or the like can be performed after the channel switching, and after decoding, The deterioration of the image quality is reduced as compared with the case of switching.

[0039]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a coded image signal switching apparatus according to the present invention. In the present embodiment, for example, the above-described MP
The coding method in the standardization plan by EG is adopted. In this embodiment, the digitally encoded image signal of each channel is exemplified by a digitally encoded image signal by satellite transmission and a digitally encoded image signal from, for example, a digital video disk as a randomly accessible recording medium. ing.

That is, in FIG. 1, for example, a digital television broadcast wave from a satellite
20. Signals modulated for digital satellite broadcasting received by these antennas 10 and 20 are demodulated by demodulation circuits 1 and 21, respectively.
Further, by channel decoding by the channel decoders 2 and 22, digitally encoded image signals (digital video bit streams) SG _A and SG _B
Is made. The signals SG _A and SG _B from the channel decoders 2 and 22 are, for example, as shown in FIG. 2A, in addition to the image data, audio data and control data in a time slot indicated by a hatched portion AD in the figure. It contains data and error correction codes.

The image data shown in FIG.
As shown in FIG. 2B which shows only the image data of FIG. 2A, a sync signal called a picture sync ps is provided at the beginning of each picture, and the picture type pt of the I picture, B picture and P picture is followed by Is added.

Further, as shown in FIG.
(Before intra-frame picture sync ps)
Contains a GOP sync code gs indicating the synchronization of the GOP.
And a GOP header gh.

Such a digitally encoded image signal SG
_A, SG _B has to be supplied to the input terminal (channel input terminal) 6, 26 of the coded image signal switching device 8 of the present embodiment. The input terminal 36 of another channel is connected to the digital video disc reproducing device 30.
Digitally encoded image signal SG _C from is to be supplied.

The coded image signal switching device 8 of the present embodiment
Digitally encoded image signals SG _A , SG _B , S compressed by the encoding method in the standardization plan by MPEG.
A switching device for switching a plurality of channels of signals such as G _C, the digitally coded image signal SG _A, S
At least an intra-frame with provided for each channel of the G _B (I-picture, the refresh frame)
FIFO (firsr-in) which is a memory means for writing / reading the digitally encoded image signals SG _A and SG _B for the interval period (1 GOP in the case of the encoding method according to the standardization scheme by MPEG). firsr-out) The memories 3 and 23 having a function as a memory and the intra frame (I) when switching from the digitally encoded image signal of the first channel to the digitally encoded image signal of the second channel. And a controller 12 for controlling a memory corresponding to the second channel so as to read from the picture.

Further, the coded image signal switching device of the present embodiment further comprises the digital coded image signals SG _A , SG
_B , SG _C is a frame completion information extracting unit that extracts information indicating the completion of a frame (a picture sync ps for each picture in the case of the encoding method according to the MPEG standardization scheme) and also extracts information of the picture type pt. Having picture sync detection circuits 4, 24, 34;
When switching from the digital coded image signal of the first channel to the digital coded image signal of the second channel, the controller 12 outputs the signal from the picture sync detection circuit corresponding to the first channel. Based on the information (picture sync detection signal), the memory corresponding to the first channel is controlled so that the digital coded image signal of the first channel is read until the frame is completed.

Further, the coded image signal switching device 8 of this embodiment has the following components in addition to the controller 12, the memories 3, 23, and the picture sync detection circuits 4, 24, 34. Is what it is.

That is, the coded image signal switching device 8 of this embodiment is provided for an interface between the operator and the device 8, and at least a channel switching designation input operation by the operator is used as a channel switching designation input signal. A man / machine interface 11 for transmitting to the controller 12, GOP sync detecting circuits 7 and 27 provided in the channels of the digitally encoded image signals SG _A and SG _B and detecting the GOP sync code gs, respectively; These GOPs
The timing of the GOP sync code gs, which is provided alongside the sync detection circuits 7 and 27 and detected by the GOP sync detection circuits 7 and 27, respectively, and the controller 12
From the memories 3 and 23 based on the control signal from
FIFO control circuit 5 for controlling reading
25 and the digitally encoded image signals SG _A and S G in response to a channel switching control signal supplied from the controller 12 based on the channel switching designation input signal.
G _B, also has a switching circuit 40 for switching the SG _C.

Hereafter, in the apparatus 8 of the present embodiment, for example, switching from the digitally encoded image signal SG _A as the first channel to the digitally encoded image signal SG _B as the second channel Will be described as an example.

[0049] First, a first digitally encoded image signal SG _A channel of the side to be switched the supplied to the channel input terminal 6, a memory having a function as and FIFO memory has a capacity of the 1GOP min 3
, And is also sent to a GOP sync detection circuit 7 for detecting the GOP sync code gs. The GO
GOP sync code g detected by P sync detection circuit 7
s is sent to the FIFO control circuit 5.

It is also assumed that the channel switching designation input operation has not yet been performed from the man / machine interface 11 at this time. That is, the controller 1
2, the channel switching designation input signal from the man / machine interface 11 has not been supplied yet.

At this time, the controller 12 performs a memory control such that if data of one GOP is written / read in the memory 3, data of the next one GOP is continuously written / read. To output a signal.
It controls the IFO control circuit 5. In other words,
FIF of the first channel system on the side to be switched
The O control circuit 5 controls the memory 3 while the channel switching designation input signal from the man / machine interface 11 is not supplied to the controller 12.
In outputting a memory control signal (address control signal) with respect to the memory 3 as read / write of the digital coded image signal SG _A at the timing based on the GOP sync code gs is made. In other words, the FIFO control circuit 5 at this time sends the first intra-frame (I
Picture 0), address 0,
.., And at the time of data reading, a memory control signal to the memory 3 is output such that data of one GOP is read in order from address 0 of the address. After the writing / reading of one GOP worth of data to / from the memory 3 is completed, the next one GO
Writing / reading of P data is performed.

The data read from the memory 3 is
The signal is sent to the channel changeover switch 8 and sent to the output terminal 41 via the channel changeover switch 8. The output signal from the output terminal 41 is transmitted to a subsequent configuration via a channel coding circuit 61 and a modulation circuit 62 and further through a cable (for example, a cable for a so-called cable television) 63.

Further, the man /
If channel switching designation input signal from the machine interface 11 is not yet supplied, the channel digitally encoded image signal supplied to the input terminal 26 SG _B also has the same capacity of 1GOP min and the memory 3 And a memory 23 having a function as a FIFO memory
And is sent to a GOP sync detection circuit 27 for detecting the GOP sync code gs. The GOP sync code gs detected by the GOP sync detection circuit 27 is sent to the FIFO control circuit 25.

[0054] At this time, the controller 12 at the time of channel switching designation input signal from the interface 11 is not yet supplied, the system of digitally encoded image signal SG _B of the second channel of the cutting switched side If writing for one GOP is performed in the memory 3 to the FIFO control circuit 25, the inside of the memory 23 is reset, and a memory control signal such that writing for the next one GOP is performed continuously is performed. Output a control signal to be output. In other words, the second side of the switching side
FIFO control circuit 25 of channel system
The GOP is stored in the memory 23 while the channel switching designation input signal from the man / machine interface 11 is not supplied to the controller 12.
And outputs a memory control signal at a timing based on the sync code gs for the memory 23 such that only the writing of the digital coded image signal SG _B is performed (address control signal). That is, at this time, the FIFO control circuit 25 stores data at address 0, address 1, address 2,... In order from the head data of the head intra frame (I picture) of the one GOP. However, the data read is not performed, and a memory control signal to the memory 23 is output such that the write reset is performed every one GOP.

Here, for example, when the operator performs a channel switching designation input operation (a switching request from the signal SG _A of the first channel to the signal SG _B of the second channel),
A channel switching designation input signal is sent from the man / machine interface 11 to the controller 12.

When the channel switching designation input signal is supplied, the controller 12 converts the information of the picture sync ps and the picture type pt from the picture sync detecting circuit 4 of the first channel system to be switched. Based on the FIFO control circuit 5
In response to this, a memory control signal is output to read out the data stored in the memory 3 up to the data immediately after the completion of the frame (immediately after the completion of the frame). In other words, after the channel switching designation input signal is supplied to the controller 12, the FIFO of the first channel system on the switching side is supplied.
The O control circuit 5 stores data from the memory 3 until the frame is completed in the GOP sync code g.
A memory control signal to be read at a timing based on s is output. Thereafter, outputs a memory control signal (address control signal) with respect to the memory 3 as only writing of the digital coded image signal SG _A at the timing based on the GOP sync code gs is made in the memory 3.

When the channel switching designation input signal is supplied, the controller 12 sends the completion of the frame from the memory 3 to the FIFO control circuit 25 of the second channel system on the switching side. Immediately after the read (completed frame) data is read, the memory 23 is controlled so as to output a memory control signal for reading 1 GOP worth of data from the beginning (from the beginning of the intra frame). In other words, after the channel switching designation input signal from the man / machine interface 11 is supplied to the controller 12, the FIFO control circuit 25 of the second channel system on the switching side reads the frame from the memory 3. Immediately after the completed (frame completed) data is read, one GOP worth of data already stored in the memory 23 is sequentially read from the memory 23 at a timing based on the GOP sync code gs. Thereafter, it outputs a memory control signal (address control signal) with respect to the memory 23 as read / write of the digital coded image signal SG _B at the timing based on the GOP sync code gs is made in the memory 23.

Further, the controller 12 supplied with the channel switching designation input signal supplies the switch circuit 40 with the last data (the last of the frame) at which the frame read from the memory 3 is completed. ,
It outputs a channel switching control signal that connects the leading data of the intra-frame of 1 GOP read from the memory 23.

As a result, signals can be connected without failure between the first and second channels switched before and after the channel switching designation input operation.

In other words, according to the apparatus 8 of the present embodiment, for example, the digitally encoded image signal SG _A of the first channel on the side to be switched before and after the channel switching designation input operation is input to the data series of FIG. and then, in the case of a second channel of the digital coded image signal SG _B of the cut-switched side the data sequence c in FIG. 2 before and after the channel switching designation input operation, for example in b of FIG. FIG. 2 arrow TS If channel switching designation input signal to the controller 12 is supplied at the timing indicated by the read from the memory 3 of the digitally coded image signal SG _a at completion point of the frame timing of the channel switching designation input signal belongs The operation is stopped, and thereafter, as shown in FIG. Reading starts from the beginning of the GOP of the digital coded image signal SG _B of 2 channels (reading start at the timing shown by the arrow RR in d of FIG. 2) is, in the first channel digitally encoded image It made to be connected with the last frame of the signal SG _a. An arrow WR in FIG. 2C indicates a timing of the write reset in the memory 23 before the channel switching.

As described above, in the case of the encoding method according to the MPEG standardization scheme, as described above, the I picture (intra frame) is self-contained only with this picture, but the P picture is the last I picture or P picture. Depending on the picture, the B picture depends on the two immediately preceding I or P pictures. Therefore, in the present embodiment, when the timing of the channel switching designation input operation is given at the time indicated by the arrow TS in FIG. 3, the digitally encoded image signal SG _A of the first channel to be switched.
On the side, it is necessary to cut immediately before the next I picture or P picture. That is, in the example of FIG. 3, the picture is cut just before the P _A8 picture. On the other hand, the cut-switched digitally encoded image signal of the second channel side SG _B, (switched) connect is from the beginning of the immediately preceding I picture back in time it is necessary. That is, FIG.
In the example, so that it is linked from the head of I _B2 picture. In the MPEG format, by performing the above-described switching, a well-connected signal SW can be obtained.

[0062] Further, in the embodiment described above, although cited satellite transmission as an example, can respond to the transmission by the optical fiber, also can cope the reproduced signal SG _C from a random accessible recording medium . At this time, in the device 8 of the present embodiment, the memory means can not be provided in the transmission signal system from the digital video disk reproducing device (or the recording and reproducing device) 30 which is the recording medium which can be randomly accessed. . That is, the memory means is provided only on the channels excluding the channel corresponding to the transmission signal SG _C from the digital video disc reproducing apparatus 30. The controller in this case 12, when switched to the channel of the transmission signal SG _C from the digital video disk reproducing apparatus 30, the reproduction apparatus 3 to read out from said intraframe
A control signal for controlling the reproduction of “0” is sent to the reproducing device 30 via the terminal 37.

Further, in the above-described embodiment, the coded image signal of the standardization plan by MPEG is used. However, the present invention is not limited to this, and it is possible to cope with a digital coded image signal of another format.

As described above, according to the present embodiment,
Since the signal can be switched without failure, for example, in a local distribution station such as a CATV station headend, an encoded program sent from a program supplier in each place can be switched, or a unique local program or CM can be switched. Can be inserted.

Further, according to the present embodiment, since the digitally coded image signal of each channel is switched without decoding, error correction or the like can be performed after switching of the channel. Image quality is less degraded than in the case of switching after the conversion.

[0066]

As described above, in the coded image signal switching device of the present invention, when switching from the first channel to the second channel, the digital code of the first channel to be switched is used. Immediately after the completion of the frame of the coded image signal, by connecting data after the intra-frame of the digitally coded image signal of the second channel to be switched, digital coding of a plurality of channels to which inter-frame coding is applied is connected. The image signal can be properly switched (signals can be connected without failure).

Further, of the digitally encoded image signal systems of each channel, the transmission signal system from a randomly accessible recording medium is controlled by controlling the reproduction of the randomly accessible recording medium so as to be read from an intra frame. In addition, no memory means is required, and the configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram illustrating a schematic configuration of a coded image signal switching device according to the present embodiment.

FIG. 2 is a diagram for explaining a state of channel switching in the apparatus of the embodiment.

FIG. 3 is a diagram for explaining a state of switching corresponding to a signal format used in the embodiment.

FIG. 4 is a diagram for explaining each prediction image.

FIG. 5 is a diagram showing a data structure.

[Explanation of symbols]

 3, 23 ... memory 4, 24, 34 ... picture sync detection circuit 5, 25 ... FIFO control circuit 7, 27 ... GOP sync detection Circuit 11 ... Man / machine interface 12 ... Controller

Claims (3)

(57) [Claims] A coded image signal switching device for switching digitally coded image signals of a plurality of channels compressed and coded by inter-frame coding, wherein the coded image signal switching device is provided for each channel and includes at least a period corresponding to an interval between intra-frames. A memory means for writing / reading the digitally coded image signal;
And control means for controlling the memory means corresponding to the second channel so as to read from an intra frame when switching to the digitally encoded image signal of the channel. Image signal switching device. 2. A frame completion information extracting means for extracting information indicating the completion of a frame from the digitally encoded image signal, wherein a second frame is obtained from the digitally encoded image signal of the first channel.
When switching to the digital coded image signal of the first channel, the control means completes the frame of the digital coded image signal of the first channel based on the information from the frame complete information extracting means. 2. The coded image signal switching device according to claim 1, wherein a memory means corresponding to the first channel is controlled so as to read out the data up to the first channel. 3. The digitally coded image signal of each channel is a satellite transmission signal, a transmission signal from an optical fiber, or a transmission signal from a randomly accessible recording medium, and the memory means is a storage device that is capable of storing the randomly accessible recording signal. 3. The coded image signal switching device according to claim 1, wherein the coded image signal switching device is provided only on a channel other than a channel corresponding to a transmission signal from a medium.