JP4371066B2 - Editing apparatus and editing method - Google Patents

Description

The present invention records a moving image signal, an audio signal, etc. on a recording medium such as a magneto-optical disk or a magnetic tape, and reproduces it for display on a display, or a video conference system, a video phone system, a broadcasting device. A digital signal editing apparatus and editing method suitable for use in the case of transmitting a moving image signal, an audio signal, etc. from a transmitting side to a receiving side via a transmission line, and receiving and displaying the received signal on the receiving side. About.

  In recent years, for example, a digital bit stream data is generated by compressing an image signal and an audio signal using a compression method of a predetermined standard, and these are multiplexed and transmitted as necessary.

  As a specific example of the above-mentioned standard, the MPEG (Moving Picture Coding Experts Group) standard can be cited. This MPEG is for the accumulation of ISO / IEC JTC1 / SC29 (International Organization for Standardization / International Electrotechnical Commission, Joint Technical Committee 1 / SuBCommittee 29: International Organization for Standardization / International Electrotechnical Commission Joint Technical Committee 1 / Technical Committee 29) This is an abbreviation for an organization that considers moving image coding. ISO11172 is the MPEG1 standard and ISO13818 is the MPEG2 standard. In these international standards, ISO11172-1 and ISO13818-1 are standardized for multimedia multiplexing, ISO11172-2 and ISO13818-2 are standardized for video, and ISO11172-3 and ISO13818-3 are standardized for audio. Has been.

  Here, in ISO11172-2 or ISO13818-2 as an image compression coding standard, an image signal is compressed and coded in units of images (frames or fields) using the correlation of the time and space directions of the images. Is what you do.

  Schematic configuration of the entire apparatus used for compressing and encoding such an image signal to generate a digital encoded bit stream and decoding the obtained bit stream via a medium such as a recording medium or a transmission medium Is shown in FIG.

  In FIG. 5, the image signal supplied to the input terminal 101 is sent to the encoding unit 102 corresponding to the so-called MPEG1 (ISO11172-2) or MPEG2 (ISO13818-2) described above and compressed and encoded. In this case, each image is a unit of compression, but since the size of the compression-encoded image data is not constant, a transmission buffer 103 is provided at the output stage, and the occupancy of this buffer is encoded. Thus, the code amount of the image is adjusted so that the transmission buffer 103 does not overflow / underflow. Also, by adjusting the code amount, a bit stream at a stable bit rate is output from the output stage of the transmission buffer 103.

  The output encoded bit stream is sent to the decoding side via a medium 105 such as a transmission medium or a storage medium. On the decoding side, the operation completely opposite to the encoding is performed. That is, the reception buffer 106 receives a bit stream transmitted at a constant rate, and the decoding device 107 reads out the encoded image data (access unit: AU) as an encoding unit from the reception buffer 106. Accordingly, reading from the reception buffer 106 is intermittent. The read image data is restored to the original image data by the decoding device 107 and is taken out from the output terminal 108.

Next, FIG. 6 is a diagram for explaining the operation of the decoding-side reception buffer (decoder buffer) 106 in FIG. FIG. 6 illustrates the occupation rate of the image bit stream input to the reception buffer 106. Image data is input to the reception buffer 106 at a constant rate, and the input at the constant rate is indicated by a straight line rising to the right. Each of the image data P1, P2, P3,... Is basically in encoding units (access unit units: AU units) at predetermined decoding times t ₁ , t ₂ , t ₃ ,. Pulled out of the buffer. For this reason, the buffer occupation amount draws a sawtooth locus as shown in FIG.

  The content of encoding such a decoder buffer so as not to overflow or underflow is the definition of VBV (Video Buffer Verifier) defined in Annex C of the standard ISO11172-2 or ISO13818-2. This content is a necessary condition for the bitstream to be recognized as satisfying the MPEG conditions.

ISO13818-2 standard

  By the way, when handling a plurality of image signals encoded based on the MPEG1 (ISO11172-2) and MPEG2 (ISO13818-2) standards as described above, bitstreams encoded independently in different systems are combined. It is generally difficult to do. In particular, a so-called seamless combination in which images are continuously combined without being frozen at the combination point is almost impossible with a bitstream generated without any limitation.

FIG. 7 shows an example in which two bit streams are simply combined. In the example of FIG. 7, the decoding of the next second bit stream BS ₂ is started immediately after the display of the first bit stream BS ₁ preceding in time is finished. Generally, at the beginning of a bit stream, a waiting time called a start-up delay is required to start decoding after accumulating a certain amount of data in a buffer. For this reason, at the connection point J, the decoding / display of the next decoded image is delayed by this delay, and a phenomenon occurs in which the display frame is frozen for several frames. Therefore, in such a case, so-called seamless reproduction cannot be performed. In FIG. 7, the data supply stops at the time point x ₁ in the figure, the last picture of the first bit stream BS ₁ is extracted at the connection point J, and the frame is frozen (still) at the time point x _2. and it combines the bit stream, the first picture at the next time point x ₃ second bit stream BS ₂ has been withdrawn.

Next, FIG. 8 shows an example in which data input to the buffer is advanced by the amount corresponding to the start-up delay in order to seamlessly reproduce the same bit stream as in FIG. In the example of FIG. 8, since seamless playback is given priority, decoding of the head image of the bit stream BS ₂ that is temporally later is performed by decoding the last image of the bit stream BS ₁ that is temporally earlier (in FIG. 8). The data is decoded after a time 1 / FR (where FR is the frame rate) (time point x _{2 in} FIG. 8) from the connection point J). In this case, the bit stream BS ₂ is input to the buffer before the decoding of the last image of the bit stream BS ₁ (the picture extracted at the connection point J) (time point x _{1 in} FIG. 8). When the last picture of BS ₁ is decoded (joining point J), the decoder buffer occupancy will cause an overflow.

  That is, it has been generally impossible to seamlessly combine the bit streams of image signals encoded by the conventional encoding method.

The present invention has been made in view of the above-described circumstances. When the bit streams of two image signals are combined, the occupation amount of the decoder buffer does not overflow or underflow, and a still image is sandwiched. It is an object of the present invention to provide a digital signal editing apparatus and an editing method that can be seamlessly combined.

In order to solve the above-described problem, the present invention provides an editing apparatus that combines bitstreams to generate a first bitstream by encoding a first image signal and to encode a second image signal. Necessary for start-up of the second bit stream so that the encoding means for generating the second bit stream by the encoding process and the decoder buffer corresponding to the reception buffer of the decoder for decoding the bit stream do not overflow or underflow the limit to secure the buffer occupancy of the decoder buffer that is, to encode provided for the end portion and the top portion of the second bit stream of the first bit stream, the encoding means A control means for controlling the encoding process; and the second bit stream after the first bit stream. And a editing means for coupling the beam at the point of attachment, the control means, the relative end portion of the first bit stream, the encoding bit rate from the restriction start time of the buffer occupancy of the first bit stream So as to secure a buffer occupation amount one frame before the extraction time of the first image from the decoder buffer with respect to the head portion of the second bit stream. The encoding process of the encoding means is controlled.

The control means sets a limit for securing a buffer occupancy amount of a decoder buffer required for start-up of the second bitstream, a bit rate at the time of encoding the end portion of the first bitstream, and the first It is preferable to control the encoding process of the encoding means so that the encoding is performed with a bit rate for encoding the head portion of the second bit stream .

Further, the control means preferably controls the encoding process of the encoding means so as to reduce the deviation of the locus of the buffer occupancy of the decoder buffer before and after the coupling point, or the control means It is preferable to control the encoding process of the encoding means so that the locus of the buffer occupancy of the decoder buffer is continuous at the coupling point.

Further, it is preferable that the encoding means performs encoding processing according to the MPEG standard, and the decoder buffer is a VBV buffer .

  According to the present invention, when combining a plurality of bit streams, the decoder buffer occupancy near the end of the first bit stream before the combining point is encoded with a first predetermined limit, In addition, since the decoder buffer occupancy near the beginning of the second bitstream after the coupling point is encoded with the second predetermined restriction, seamless coupling can be performed without buffer failure. it can.

  Here, the first and second restrictions are restrictions for securing a decoder buffer amount necessary for the start-up of the second bit stream, and the first and second encoded data are added with such a restriction. By combining these bitstreams, two video bitstreams that have been compression-encoded using MPEG1 (ISO11172-2) or MPEG2 (ISO13818-2) can be maintained in compliance with VBV (Video Buffer Verifier) regulations. In addition, it is possible to continuously combine the bitstreams without causing the image display to freeze (still).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram for explaining an embodiment of the present invention. In the embodiment shown in FIG. 1, after the first bit stream obtained by encoding the first image signal supplied to the input terminal 11 by the encoding device 10, it is supplied to the input terminal 21. It is assumed that the second bit stream obtained by encoding the second image signal with the encoding device 20 is combined.

  The first image signal supplied to the input terminal 11 of the encoding apparatus 10 in FIG. 1 is sent to the encoding unit 12 corresponding to the so-called MPEG1 (ISO11172-2) or MPEG2 (ISO13818-2) and compressed. It is encoded and extracted as a first bit stream. In this case, each image is a unit of compression. However, since the size of the compression-encoded image data is not constant, a transmission buffer 13 is provided in the output stage to encode the occupied amount of this buffer. By feeding back, the code amount of the image is adjusted so that the transmission buffer 13 does not overflow / underflow. At this time, encoding is performed with a restriction on the decoder buffer occupancy near the end of the first bit stream obtained by encoding the first image signal, and in particular, concatenation after the first bit stream. A restriction is provided for the buffer occupancy near the end of the first bit stream in order to secure the decoder buffer amount required for the startup of the second bit stream. This restriction is applied according to the control signal from the terminal 14, and the contents will be described later with reference to FIG.

  Further, the second image signal supplied to the input terminal 21 of the encoding device 20 is sent to the encoding unit 22 corresponding to MPEG1 (ISO11172-2) or MPEG2 (ISO13818-2) and compressed in the same manner as described above. Encoded to be the second bit stream, but by providing a transmission buffer 23 at the output stage and feeding back the occupied amount of this buffer to the encoding device, the transmission buffer 23 is prevented from overflowing / underflowing. The code amount of the image is adjusted. At this time, a limit is set for the buffer occupation amount near the end of the second bit stream, and in particular, the limit for securing the buffer amount required for the start-up of the second bit stream is the first limit. It is provided for the buffer occupation amount near the end of two bit streams. This restriction is applied in accordance with a control signal from the terminal 24, and the contents will be described later with reference to FIG.

  The first bit stream from the encoding device 10 and the second bit stream from the encoding device 20 are combined in the bit stream combining unit 30 in the order of the second bit stream after the first bit stream, It is taken out from the output terminal 36. This coupling will be described later with reference to FIG.

  In other words, the encoding apparatus 10 encodes the first and second bitstreams combined by the combining unit 30 with a restriction on the buffer occupancy in the vicinity of the end of the first bitstream that is temporally previous. In addition, the encoding apparatus 20 encodes the above-described MPEG1 (ISO11172-2) or MPEG2 (ISO13818-) by setting a certain limit on the buffer occupancy at the beginning of the second bitstream that is temporally behind. The VBV (Video Buffer Verifier) stipulated in 2) is observed, and it is combined seamlessly, that is, so that images can be displayed continuously without freezing.

  This is because, when seamless coupling is performed at the coupling point, there is a possibility that the decoder buffer overflow as described in the above-described conventional example may occur. In view of this, encoding control is performed before and after the coupling point.

Specifically, the bit rate near the end of the _first bit stream BS ₁ located before the joining point J is limited as shown in FIG. Here, it is assumed that α is a buffer amount necessary for start-up when the second bit stream to be connected is seamlessly connected in advance. The buffer amount α is set to an appropriate value in actual operation. The encoding bit rate is represented by R _B , the total capacity of the buffer is BF, and the extraction time of the last image from the buffer is T.

In this case, if the time of the connection point J is T,
T- (α / R _B )
Since this time is t = 0, the direction of time advance is positive, and the buffer occupancy is expressed as a function of t.
BO (t) = BF−R _B × t
In this way, the vicinity of the end of the bitstream before the combination is encoded. This is a restriction on the _first bitstream BS1 before the coupling point. In FIG. 1, the control signal from the terminal 14 is given to the encoding unit 12, so that the above-described restriction is added when encoding near the end of the bit stream.

Similarly, the bit rate in the vicinity of the head of the _second bit stream BS2 located after the connection point J is limited as shown in FIG. As the buffer occupancy of the 1 / R _F before the display time of the first frame is less than the alpha, it is not kept to limit the bit rate at the time of startup. That is, when the extraction time from the buffer of the first picture of the _second bit stream BS ₂ is T ′ and the frame rate is R _F , the buffer occupancy at the time of (T′−1 / R _F ) the amount beta is, the second bit stream BS ₂ relative seamless buffer amount required for startup when linked to the α determined in advance, beta <added α become such restrictions, behind the second encoding a first portion of the bit stream BS _2. In FIG. 1, the control signal from the terminal 24 is given to the encoding unit 22, so that the above-described restriction is added when encoding near the head of the bit stream.

  The VBV_dilay in FIG. 3 is necessary for the picture extracted in the buffer on the decoder side according to the definition of VBV (Video Buffer Verifier) defined in MPEG1 (ISO11172-2) or MPEG2 (ISO13818-2). The amount of buffer storage to be performed is shown in time, and the picture of the first display unit is extracted from the buffer and decoded at the time (T ′) when the VBV_dilay period has elapsed since the start of the supply of the bit stream to the decoder. Is done.

  A specific example of the case where the first and second bitstreams encoded with the restrictions described with reference to FIGS. 2 and 3 are sent to the bitstream combining unit 30 in FIG. This will be described with reference to FIG.

FIG. 4 shows a specific example in which those encoded according to the above-described conditions are combined. In this case, the first end portion of the bitstream BS ₁ before, in order to have a minute buffer occupancy of the alpha, the minute startup delay-converted alpha / R _B this time as a margin Combining the subsequent _second bitstream BS2 does not cause a buffer overflow. Further, in the actual combination, the sequence_end_code (sequence end code) of the last part of the previous first bit stream BS ₁ is deleted, and the deleted sequence_end_code and (α−β) are filled with bits (bit By performing (stuffing), it is possible to achieve a consistent connection.

In other words, the first bit stream BS ₁ is encoded by the first encoding device 10 so as to suppress the last rate control of the first bit stream BS ₁ to the overflow level BO (t) using the α, and the second bit stream BS ₂ At the beginning, the second encoding device 20 performs encoding so that the buffer occupancy β at time (T′−1 / R _F ) is smaller than the above α (β <α). been buffer is guaranteed not to overflow even if, for the sequence_end_code the first bit stream BS ₁ beauty end portion difference and is the deletion of the α and beta, filling the invalid data (e.g., 0, etc.) Thus, bit stream combining is realized while maintaining the prescribed consistency of MPEG VBV (Video Buffer Verifier).

Here, in the bit stream combining unit 30 of FIG. 1, the sequence_end_code of the last part of the _first bit stream BS ₁ from the encoding device 10 is detected by the demultiplexer 31 and sent to the CPU 35. The sequence_start_code (sequence start code) of the head portion of the second bit stream BS ₂ from 20 is detected by the demultiplexer 32 and sent to the CPU 35. The first and second bit streams BS ₁ and BS ₂ from these demultiplexers 31 and 32 are respectively sent to the selected terminals a and b of the changeover switch 34, and the third selection of the changeover switch 34 is selected. A bit for filling from the bit filling circuit 33 is supplied to the terminal c. The changeover switch 34 is controlled by a control signal from the CPU 35. The CPU 35 determines the sequence_end_code of the last part of the _first bit stream BS ₁ from the demultiplexers 31 and 32 and the second bit stream BS _2. The sequence switch 34 is sequentially switched and connected to b via the selected terminal a to c based on the sequence_start_code of the head portion of the first portion, thereby deleting the sequence_end_code of the last portion of the _first bit stream BS ₁ , This sequence_end_code and the above α-β are supplemented with a filling bit (stuffing bit) ST from the bit filling circuit 33 and connected to the _second bit stream BS2. An output bit stream from the changeover switch 34 is taken out via an output terminal 36.

By the way, the above is an example when the second bit stream output from the encoding device 20 is connected after the first bit stream output from the encoding device 10. When the bitstream output from the encoding device 10 is combined after the bitstream, the overflow level BO (t) based on the buffer amount α is suppressed near the end of the bitstream output from the encoding device 20. Thus, the buffer occupancy β at time (T′−1 / R _F ) is smaller than α at the head of the bitstream output from the encoder 10. What is necessary is just to restrict | limit the encoding in the encoding apparatus 10 like ((beta) <(alpha)). In this case, the bitstream combining unit 30 detects the sequence_end_code at the end of the bitstream output from the encoding device 20 by the demultiplexer 32 and sends it to the CPU 35, and the demultiplexer 31 outputs from the encoding device 10. The sequence_start_code at the head of the bitstream thus detected is detected and sent to the CPU 35. Based on these pieces of information, the CPU 35 performs switching control in the order of “a” through the selected terminal “b” to “c” of the changeover switch 34, deletes the sequence_end_code at the end of the bitstream output from the encoding device 20, After the filling bits from the bit filling circuit 33 are filled by the sequence_end_code and (α−β), the bit stream output from the encoding device 10 is connected and sent to the output terminal 36.

  In addition, for one bit stream output from the encoding device 10, the first portion of the bit stream is encoded with the restriction shown in FIG. 3, and the restriction shown in FIG. 2 is added to the end portion of the bit stream. By performing the above encoding, it becomes possible to combine other bit streams before and after the bit stream.

As a specific example of the system to which the configuration of FIG. 1 as described above is applied, for example, a broadcasting network in which a main broadcasting station and a local broadcasting station are connected via a broadcasting satellite or the like can be cited. . In this broadcasting network, a program from a main broadcasting station is encoded by the encoding device 10 and provided to each local station. Each local station encodes local news, CMs, and the like for each region by the encoding device 20. These are combined, taken out from the output terminal 36, and sent to the respective areas. At this time, for the end part of the bit stream of the broadcast program from the main station, the encoding with the limitation that the buffer occupancy does not exceed BO (t) = BF−R _B t described with reference to FIG. As described above with reference to FIG. 3, the buffer occupancy β at the time (T′−1 / R _F ) is applied to the head part of the bit stream of the signal from the local station to be combined thereafter. Is encoded with a restriction that does not exceed the buffer amount α (β <α), and the bit stream obtained by seamlessly combining these including bit filling in the combining unit 30 In the decoding, there is no buffer failure, that is, no buffer overflow or underflow occurs.

  According to the embodiment as described above, when two video bit streams compression-encoded using an MPEG1 (ISO11172-2) or MPEG2 (ISO13818-2) image signal are combined, The above-mentioned VBV (Video Buffer Verifier) regulations can be observed, and the images can be seamlessly combined so that they can be displayed continuously without being frozen.

  According to the embodiment of the present invention as described above, when a plurality of bit streams are combined, the first predetermined amount with respect to the decoder buffer occupancy near the end of the first bit stream before the combining point is determined. Is encoded, and the decoder buffer occupancy near the beginning of the second bitstream after the combination point is encoded with the second predetermined limit, so that seamless combination is possible. Can be performed without buffer failure.

  Here, the first and second restrictions are restrictions for securing a decoder buffer amount necessary for the start-up of the second bit stream, and the first and second encoded data are added with such a restriction. By combining these bitstreams, two video bitstreams that have been compression-encoded using MPEG1 (ISO11172-2) or MPEG2 (ISO13818-2) can be maintained in compliance with VBV (Video Buffer Verifier) regulations. In addition, it is possible to continuously combine the bitstreams without causing the image display to freeze (still).

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

It is a block diagram which shows schematic structure of the system which couple | bonds the bit stream from the encoding system of 2 systems for describing embodiment of this invention. It is a figure for demonstrating the restriction | limiting at the time of the encoding of the 1st bit stream before the connection point in embodiment of this invention. It is a figure for demonstrating the restriction | limiting at the time of the encoding of the 2nd bit stream after the joining point in embodiment of this invention. It is a figure for demonstrating the coupling | bonding of the 1st bit stream and 2nd bit stream in embodiment of this invention. It is a block diagram which shows schematic structure of the system which consists of an image signal encoding apparatus and a decoding apparatus. It is a figure which shows the change of the buffer occupation amount of a receiving buffer (decoder buffer). It is a figure for demonstrating the example of the coupling | bonding accompanying the freeze (still) of the frame of two bit streams. It is a figure for demonstrating the example in the case of couple | bonding two bitstreams seamlessly.

Explanation of symbols

10,20 encoding device, 12,22 encoding unit, 13,23 transmission buffer, 30 bit stream combining unit, 31,32 demultiplexer, 33 bit filling circuit, 34 changeover switch, 35 CPU

Claims (6)

In an editing device that combines bitstreams,
Encoding means for encoding a first image signal to generate a first bit stream, and encoding a second image signal to generate a second bit stream;
In order to prevent the decoder buffer corresponding to the reception buffer of the decoder that decodes the bitstream from overflowing or underflowing, the restriction for securing the buffer occupancy of the decoder buffer required for the startup of the second bitstream is set as described above. to encode provided for the end portion and the top portion of the second bit stream of one bit stream, and control means for controlling the encoding processing in the encoding means,
Editing means for combining the second bit stream at a connection point after the first bit stream ;
The control means secures a buffer occupancy that decreases at a rate of an encoding bit rate from a restriction start time of the buffer occupancy of the first bitstream for the end portion of the first bitstream, An editing apparatus for controlling the encoding process of the encoding means so as to secure the buffer occupation amount one frame before the extraction time of the first image from the decoder buffer with respect to the head portion of the second bit stream . The editing apparatus according to claim 1, wherein the control means controls the encoding process of the encoding means so as to reduce a shift of the locus of the buffer occupation amount of the decoder buffer before and after the coupling point. The editing apparatus according to claim 1, wherein the control means controls the encoding process of the encoding means so that the locus of the buffer occupation amount of the decoder buffer is continuous at the coupling point. The encoding means performs encoding processing according to the MPEG standard,
The editing apparatus according to claim 1, wherein the decoder buffer is a VBV buffer. The control means deletes the sequence_end_code at the end portion of the first bitstream,
The editing apparatus according to claim 1, wherein the control means controls the encoding process of the encoding means so as to supplement stuffing bits at the end portion of the first bit stream. In an editing method that combines bitstreams,
An encoding step of encoding the first image signal to generate a first bit stream and encoding the second image signal to generate a second bit stream;
In order to prevent the decoder buffer corresponding to the reception buffer of the decoder that decodes the bitstream from overflowing or underflowing, the restriction for securing the buffer occupancy of the decoder buffer required for the startup of the second bitstream is set as described above. to encode provided for the end portion and the top portion of the second bit stream of one bit stream, and a control step of controlling the encoding processing in the encoding step,
An editing step of combining the second bitstream at a connection point after the first bitstream ,
In the control step, with respect to the end portion of the first bit stream, a buffer occupancy amount that decreases at a coding bit rate rate from the start time limit of the buffer occupancy amount of the first bit stream is secured, and Editing method for controlling the encoding process of the encoding means so as to secure the buffer occupation amount one frame before the extraction time of the first image from the decoder buffer with respect to the head portion of the second bit stream .

Images