KR100312411B1 - A conversion method of the compressed moving video on the video communication system - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a compressed video conversion method in an image system.

2. The technical problem to be solved by the invention

The present invention utilizes the information generated according to a compression algorithm common among heterogeneous videos in a variable length code, which is a fully compressed region of a video system, and provides syntax structures and other processing parameters that hinder the conversion between two other codes. To provide a compressed video conversion method for converting MPEG-2 standard video compression code directly into standard video compression code conforming to H.263.

3. Summary of Solution to Invention

According to an aspect of the present invention, there is provided a method of converting a compressed video applied to an image system, comprising: a first step of analyzing header information of an MPEG-2 stream and deleting a sequence layer and a video group (GOP) layer; And generating hierarchical information on the remaining images of the MPEG-2 stream, and compressing the compressed video of the MPEG-2 stream into a H.263 stream in a variable length code, in which a specific parameter value required for each layer is a fully compressed region. The second step of converting to a video.

4. Important uses of the invention

The present invention is used in the field of compressed video in an image system.

Description

A conversion method of the compressed moving video on the video communication system}

The present invention converts the MPEG-2 (MPEG-2: Moving Picture Expert Group-2) standard video compression code into a standard video compression code that conforms to the form of H.263 in a variable length code that is a completely compressed region of a video system. The present invention relates to a compressed video conversion method that enables easy conversion between videos.

In general, the conversion between heterogeneous image codes may be defined as a function that enables mutual compatibility by converting a code system made using different compression schemes into a desired compression syntax. This is called a transcoder, and the most common transcoder is a method of a pixel region that decodes a compressed code into a linear pulse code modulation (PCM) signal and encodes the compressed code into a compressed code that needs to be interlocked again. The processing method in such a pixel region is shown in FIG.

1 is a diagram illustrating a code conversion process in a conventional pixel area.

The transcoder of the pixel region is the most easily accessible method of converting heterogeneous images, but this requires a decoder and encoder pair for conversion, which is a dual economic burden regardless of whether a function exists in a network node or a user terminal. In addition to the loss and complexity of implementation, the transcoder of the pixel region may be used, and thus, the deteriorated image quality of the converted image may occur, and in particular, an unacceptable delay may occur in multimedia communication.

As a conventional method, there is a method (GIF to JPEG) for converting a Graphics Interchange Format (GIF) to a Joint Photographics Expert Group (JPEG).

Here, GIF is an image and graphic standard for general computers. It converts high-resolution information according to its purpose using Palette, a look-up table, and converts color information during this process. The index value to be expressed is compressed by the "Lempel-Ziv-Welch (LZW) algorithm".

On the other hand, JPEG is a standard for compressing continuous-tone still images such as photographs. This algorithm aims to convert GIF, which is widely used for displaying image and graphic information, to JPEG on the World Wide Web (WWW) of the Internet, and to reduce the file size by 10-50%. .

On the other hand, the research on "Motion JPEG to MPEG-1" conversion is performed by changing the compression code into a form that an MPEG-1 decoder can process an MJPEG video composed of independent Intra frames. Syntax changes and parts of MPEG-1, such as I, P (Predictive coded picture), B (Bidirectionally predictive coded picture) frames, and motion vectors, without generating a motion vector, such as sequences and group of picture headers. It is a simple structure for changing parameters, which is the main focus of research on enabling image editing in MPEG-1 as in JPEG, rather than converting to full MPEG-1 compression.

Besides, there is a study of converting MPEG-1 / 2 video into MJPEG in the compressed region, but this is also a method in which image editing is a main application.

As such, the video compression method has clearly distinguished applications using H.261 of "ITU-T" for interactive communication and MPEG-1 of "ISO / IEC" for storage and distributed communication. Further research Standardized H.263 and MPEG-2 have expanded their application areas to cover all multimedia communication services. This means that two compression methods can be used for the same purpose, and the compressed video algorithms of these two international standards organizations (ITU-T, ISO / IEC) are dependent on the performance of the compression method in interdependent relationships that complement each other's functions. The superiority was thus transformed into the competition of choice.

H.263 and MPEG-2, which are recommended by the International Organization for Standardization, are compression methods that target the same video, but cannot interoperate. That is, H.263 encoded streams cannot be processed by the MPEG-2 decoder, and MPEG-2 streams cannot be decoded by H.263. This did not cause major problems in H.261 and MPEG-1, which were primarily used for video telephony, video conferencing, and storage, but extended to real-time interactive communications, broadcast, communication services, and storage communications. H.263 and MPEG-2 inevitably use these compression schemes for the same purpose, and the inability to interoperate between them causes economic loss on the user side and heterogeneity on the application side.

This heterogeneity of the application side can be solved by using a corresponding decoder and a transcoder in a general pixel area connecting the encoder in multiple stages, but this also can be duplicated regardless of the position of the transcoder (network or user terminal). It is an economic burden. In addition, the use of a transcoder, which is a multi-stage codec, causes deterioration in image quality, particularly excessive processing delay, thereby limiting real-time communication.

Therefore, unlike H.261 and MPEG-1, which failed to establish the network and spread the generalized communication service due to immaturity of the multimedia market, public switched telephone network (PSTN) and local area network (LAN) Considering the current situation where the network infrastructure such as Area Network (ATM), Asynchronous Trasfer Mode (ATM), Cable Television (CATV), and digital airwaves is mostly completed, and the public's familiarity with multimedia, Various multimedia communication services using MPEG-2 will spread rapidly.

Accordingly, mutual interworking between these heterogeneous compression codes, which is currently impossible, has become a problem that must be solved.

Resolving heterogeneity from the perspective of application services and interworking of heterogeneous compression codes to provide economic advantages must be provided to ensure the efficiency that can be realized at an affordable price and the real time processing required for multimedia communication.

As mentioned above, unlike the existing standard, which clearly distinguished and recommended the field of application of video compression code, it is mainly used now and the compression code algorithm newly researched is targeted for the same application. That is, if these heterogeneous video compression schemes are used for the same multimedia communication, application services between endpoints cannot be interworked.

In an attempt to solve the problem of heterogeneity due to the difference of video compression methods, there have been studies of ITU-T and ISO / IEC, but this is also limited to unidirectional interworking that accepts the basic compression code of H.263 in MPEG-4. So far, the interworking from MPEG-4 to H.263 has not been resolved.

In particular, it is impossible to interoperate between MPEG-2 and H.263, which has emerged as a representative video compression algorithm, and when such heterogeneous compression codes are used for multimedia application services including interactive, communication, and broadcasting, communication is impossible. In addition to the problem, in order to receive a specific video application service, there is a problem of economic loss of the user side that requires a separate video compression processing unit for each service.

In order to solve the above problems, the present invention utilizes the information generated according to a compression algorithm common among heterogeneous videos in a variable length code, which is a completely compressed region of an image system, and converts two other codes. A computer recording a compressed video conversion method for directly converting MPEG-2 standard video compression codes into standard video compression codes conforming to H.263 by converting necessary syntax structures and other processing parameters and a program for realizing the same. The purpose is to provide a recording medium that can be read by.

1 is a code change process diagram of a conventional pixel region.

2 is a flowchart illustrating an embodiment of a method for converting a compressed video according to the present invention.

3 is an explanatory diagram showing the conversion relationship between layers of an MPEG-2 stream and an H.263 stream used in the present invention;

4 is an explanatory diagram showing a conversion relationship between a macroblock layer of an MPEG-2 stream and an H.263 stream used in the present invention;

5A and 5B are explanatory diagrams of a DC coefficient encoding process from an MPEG-2 stream to an H.263 stream for a block layer used in the present invention.

In accordance with another aspect of the present invention, there is provided a compressed video conversion method applied to a video system, comprising: a first step of analyzing header information of an MPEG-2 stream and deleting a sequence layer and a video group (GOP) layer; And generating hierarchical information on the remaining images of the MPEG-2 stream, and compressing the compressed video of the MPEG-2 stream into a H.263 stream in a variable length code, in which a specific parameter value required for each layer is a fully compressed region. The second step of converting to a video.

The present invention also provides a video system having a processor, comprising: a first function of interpreting header information of an MPEG-2 stream to delete a sequence layer and a video group (GOP) layer; And generating hierarchical information on the remaining images of the MPEG-2 stream, and compressing the compressed video of the MPEG-2 stream into a H.263 stream in a variable length code, in which a specific parameter value required for each layer is a fully compressed region. A computer readable recording medium having recorded thereon a program for realizing a second function of converting to a moving picture is provided.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a flowchart illustrating a method of converting a compressed video into an H.263 compressed video according to an embodiment of the present invention.

As shown in FIG. 2, the compressed video converting method of converting MPEG-2 compressed video into H.263 compressed video according to the present invention first analyzes header information of an MPEG-2 stream to obtain a sequence layer and a video group (GOP). Delete the group (Group Of Picture) layer (201).

Then, for the remaining pictures of the stream (206), the frames of the MPEG-2 stream and the H.263 stream are matched to generate a video layer of the H.263 stream (202), and the resolution and macroblock of the MPEG-2 stream. In step 203, a block group (GOB) layer of the H.263 stream is generated by analyzing the information of the H.263 stream.

Next, for the remaining pictures of the stream (206), the information of the macroblock in the MPEG-2 stream is analyzed and converted into an H.263 macroblock layer (204), and the information of the block layer of the MPEG-2 stream is analyzed. To a block layer of the H.263 stream (205).

The compressed video converting method for converting MPEG-2 compressed video into H.263 compressed video according to the present invention is a new method that satisfies the requirements of transcoder, and it is differentiated both H.263 and MPEG-2. Based on the motion estimation, compensation, Discrete Cosine Transform (DCT) and entropy coding according to Pulse Code Modulation (DPCM), information generated according to a common compression algorithm Is to make the most of it, and converts the syntax and other parameters necessary for processing other obstacles.

Accordingly, the present invention converts the MPEG-2 compression code into a video code conforming to the H.263 format, and performs the processing on the fully compressed syntax, which has the advantages of image quality improvement and real-time conversion, and is particularly easy with simple processing. It is an efficient way to implement it.

A compressed video conversion method for converting an MPEG-2 compressed video according to the present invention as described above into an H.263 compressed video will be described in more detail with reference to FIGS. 3 to 5.

3 is an explanatory diagram showing the conversion relationship between layers of an MPEG-2 stream and an H.263 stream used in the present invention.

In the present embodiment, it is possible to convert heterogeneous video codes by a simple procedure of generating and removing hierarchical information necessary for a fully compressed sub picture and changing specific parameter values required for each layer.

As shown in FIG. 3, the compressed video conversion from the MPEG-2 stream 3a to the H.263 stream 3b is performed when the MPEG-2 stream 3a is encoded at a constant bit rate (CBR). In this case, a process of requantizing a specific macroblock is required. This is because the quantization parameter of the quantization parameter of the H.263 stream 3b applied in units of macroblocks is limited, and thus cannot accommodate the quantization parameter of the MPEG-2 stream 3a, which may have an arbitrary value.

Therefore, if the difference between the quantization parameter value of the previous macroblock is ± 1 ~ ± 2 or more, inverse quantization is required, and then the quantization parameter value is set to a value within the range of ± 1 ~ ± 2 to requantize the normal conversion. . This part is about the conversion of the macroblock layer, but since the MPEG-2 stream 3a is determined by encoding CBR or Variable Bit Rate (VBR), the description will be briefly described.

In addition, in the case of changing the video compression code from the MPEG-2 stream 3a to the H.263 stream 3b, the algorithm and details used will be described in detail for each layer.

Since the sequence layer and the GOP layer of the MPEG-2 stream 3a have no layer corresponding to H.263, the necessary parameters are analyzed and then removed. That is, when the type of the current input layer is a sequence or a GOP layer by analyzing the MPEG-2 stream 3a to be processed, the resolution, the quantization matrix, the structural information of the frame, etc. are analyzed to convert the compressed syntax. Use as information. The dual quantization matrix is a different element in the quantization procedure of the H.263 stream 3b and the MPEG-2 stream 3a. In this case, since the quantization of the MPEG-2 stream 3a uses the matrix as weighting information for the Discrete Cosine Trasform (DCT) block, it is necessary to analyze the exact value of the quantization matrix included in the sequence layer. It is possible to convert the H.263 stream 3b to the video code without using the code.

The conversion of the video layer converts I, P, and B frames into I, PB, which are corresponding frame types of the H.263 stream 3b, through frame type analysis of the input MPEG-2 stream 3a.

Unlike the MPEG-2 stream 3a in which the slice layer 301 and the macroblock layer 302 have quantization parameter values, the H.263 stream 3b has a quantization parameter in the picture layer. However, this too does not mean as much as the quantization parameter in the slice layer of the MPEG-2 stream 3a. That is, corresponding parameters present in the picture layer and slice layer 301 of the H.263 stream 3b and the MPEG-2 stream 3a are updated by the quantization parameter of the macroblock, so The quantization parameter value in the slice layer 301 of the H.263 stream 3b is used without change in the picture layer of the H.263 stream 3b.

While the slice layer 301 of the MPEG-2 stream 3a has a clear purpose, the GOB layer 311 of the H.263 stream 3b is named H.261 and the structure of the MPEG-2 stream ( Introduced in 3a), the nature of the syntax hierarchy of the entire H.263 compressed image is unclear. That is, in the H.263 stream 3b, the GOB layer 311 can be regarded as a surplus layer that inherits only the syntax structure of the H.261 stream, as has the option of replacing the GOB layer 311 with the slice layer 301. .

Therefore, when changing the slice layer 301 of the MPEG-2 stream 3a, the GOB layer 311 as described above is based on the fact that the H.263 stream 3b does not include the GOB layer 311. There is no obvious use of it, so don't create a GOB. Coded macroblock indication (COD) for all macroblocks converted to H.263 stream 3b to preserve the characteristics of the macroblock of MPEG-2 stream 3a, which may be omitted depending on the code type of the data. Add to

In order to convert from the macroblock of the MPEG-2 stream 3a to the macroblock of the H.263 stream 3b, it is necessary to interpret the information on the corresponding layer of the MPEG-2 stream 3a. Here, the information to be analyzed is the coding type, type, coded block pattern (CBP) and motion vector of the macroblock.

Since the H.263 stream 3b does not use information indicating the location of the macroblock, such as the macroblock address increment (MBAI) of the MPEG-2 stream 3a, the location of the macroblock is H.263. This can be found by analyzing the COD of stream 3b. Since this indicates the presence or absence of encoding of the macroblock, the COD may be regarded as corresponding to the MBAI of the MPEG-2 stream 3a.

However, in the first intra frame of the H.263 stream 3b, since all macroblocks are intra and cannot be omitted accordingly, no COD is used to increase the compression efficiency.

H.263 stream 3b has only the first one frame unless the intra frame is specially encoded, so that the compression efficiency of COD erasure is not high. However, the H.263 stream 3b of the MPEG-2 stream 3a is periodically repeated for each GOP layer. When changing an I frame to an H.263 stream (3b), the presence or absence of this COD has a significant impact on the bit rate of the converted stream. Therefore, when converting an I frame of the MPEG-2 stream 3a into an intra frame of the H.263 stream 3b for the bit efficiency of the stream, no COD is generated.

In order to appropriately convert the macroblock type of the MPEG-2 stream 3a into the H.263 stream 3b, the corresponding hierarchical information of the MPEG-2 stream 3a is analyzed and the H.263 stream 3b is analyzed. You need to adapt the syntax to That is, the macroblock type & coded block pattern for chrominance (MCBPC) representing the type of the macroblock in the H.263 stream 3b is a quantization parameter included in the macroblock of the MPEG-2 stream 3a in order to generate this reasonably. , A coding form of a color difference signal, a motion vector, and the like are required, and the macroblock type of the H.263 stream 3b is determined based on this.

4 is an explanatory diagram showing a conversion relationship between a macroblock layer of an MPEG-2 stream and an H.263 stream used in the present invention.

The macroblock types of the MPEG-2 stream 4a are clearly distinguished, while the H.263 stream 4b needs to combine several pieces of information in order to know the exact macroblock characteristics.

Therefore, as shown in Fig. 4, the type matching of the macroblock is performed after analyzing the CBP information of the MPEG-2 stream 4a and preparing the code type of the H.263 stream 4b based on this. Process by using look-up table.

The MPEG-2 stream 4a and the H.263 stream 4b use similar algorithms for motion estimation and compensation, but the methods for encoding the resulting motion vectors are different. Here, the transformation of the motion vector solves the difference in the encoding method for the motion vector between two heterogeneous compressed codes, and restores the original absolute motion estimate from the motion vector of the MPEG-2 stream 4a represented by the difference value. This is again performed through motion vector encoding used in the H.263 stream 4b to complete the motion vector conversion for the macroblock.

If there is no motion through the comparison with the previous frame, unlike the MPEG-2 stream 4a which expresses no motion vector, the H.263 stream 4b is configured to display the motion vector for all inter macroblocks. Doing. That is, when there is no motion, the corresponding vector value is set to 0.

Therefore, in order to solve the difference between the two compression codes, the vector value of the macroblock of the MPEG-2 stream 4a without the motion vector is set to 0 like the H.263 stream 4b. However, unlike the motion vector of the H.263 stream 4b, which has an absolute value, the motion vector of the MPEG-2 stream 4a is encoded with a differential value, and according to the state of the previous macroblock and the position of the block. Since the meanings are different, the exact calculation is performed to obtain a vector according to the actual motion estimation, and then the motion vector is encoded according to the method used in the H.263 stream 4b.

As described above, the conversion of the macroblock unit applied to the VBR stream is performed by converting the quantization parameter of the H.263 stream 4b into a quantization parameter that is varied to an arbitrary value with respect to the CBR-encoded MPEG-2 stream 4a as described above. Heterogeneous video code conversion without loss of picture quality should be processed to meet the encoding conditions. In other words, in the MPEG-2 stream 4a, all values of the quantization parameter of the macroblock are allowed to be in the range of 1 to 31, whereas the H.263 stream 4b can be up to 2 based on the previous macroblock. Only variation is allowed. Therefore, it is impossible to use the quantization parameter value of the MPEG-2 stream 4a without change.

The quantization parameter conversion of the CBR stream is used unchanged when the difference between parameter values of the macroblock of the MEG-2 stream 4a is within 2, and when exceeded, the value is adjusted within the allowable range through requantization. That is, if the parameter of the macroblock has a value of +2 or more, the value of the quantized parameter is set to be the same as the quantization parameter of the previous macroblock. This is to minimize the deterioration in image quality. As a result, the converted image has a higher bit rate characteristic than the original stream, and the deterioration in image quality by the quantization error occurs.

In converting the CBR-encoded MPEG-2 stream 4a to the H.263 stream 4b, the bit rate increase and the image quality deterioration occurring are dependent on the distribution and variation of the quantization parameters of the macroblock constituting the frame.

On the other hand, block layer processing requires conversion of DC (Direct Current) coefficients of the intra DCT block and other DC and AC (Alternative Current) coefficients. The DC coefficient encoding process from the MPEG-2 stream 4a to the H.263 stream 4b for the block layer is illustrated in FIGS. 5A and 5B.

In the MPEG-2 stream 4a, the DCT block expresses the DC component as a difference value from the previous block, and the other parts of the AC coefficient and the DC and AC of the inter block represent a run-length code (RLC). After that, it is encoded by a two-dimensional variable length code (VLC). In order to change this to a form representing a block of the H.263 stream 4b, the block of the MPEG-2 stream 4a is variable length decoded (VLD), and a DC coefficient expressed as a difference value is obtained. Convert to 8-bit fixed length code (FLC) used in H.263 stream (4b), and the remaining coefficients are three-dimensional VLC expressed in RUN, LEVEL, and LAST. Processing is performed to complete the conversion between blocks.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains, and the above-described embodiments and accompanying It is not limited to the drawing.

As described above, the present invention does not perform motion estimation, compensation, and discrete cosine transform (DCT) related processing in converting MPEG-2 video compression codes to H.263 compression codes. It is easy to implement the configuration, real-time processing, which is a necessary requirement for image quality improvement and multimedia communication, and various multimedia communication without purchasing a separate device when using these heterogeneous compression codes for video conferencing or video on demand. There is an effect that can provide a service.

Claims (5)

In the compressed video conversion method applied to the imaging system, Parsing the header information of the MPEG-2 stream to delete the sequence layer and the video group (GOP) layer; And For the remaining images of the MPEG-2 stream, hierarchical information is generated, and the compressed video of the MPEG-2 stream is compressed video of the H.263 stream in a variable length code indicating a specific parameter value required for each layer. Second step to convert Compressed video conversion method comprising a. The method of claim 1, The first step is, When the header information of the MPEG-2 stream is interpreted and the type of the currently input layer is either a sequence layer or an image group layer, since there is no layer corresponding to the H.263 stream, the resolution, A method of converting a compressed video, characterized by removing the quantization matrix and frame information after analyzing the structural information and using the information as basic information for transforming a compressed syntax. The method of claim 1, The second step, Generating a video layer of the H.263 stream by matching frames of the MPEG-2 stream and the H.263 stream with respect to the remaining images of the MPEG-2 stream; A fourth step of generating a block group (GOB) layer of the H.263 stream by analyzing the resolution and macroblock information of the MPEG-2 stream; A fifth step of analyzing information of the macroblock in the MPEG-2 stream and converting the macroblock into a macroblock layer of the H.263 stream; And A sixth step of analyzing information of the block layer of the MPEG-2 stream and converting the information into a block layer of the H.263 stream; Compressed video conversion method comprising a. The method of claim 3, wherein The fifth step, And converting the coding type, type, coded block pattern (CBP), and motion vector information of the macroblock of the macroblock in the MPEG-2 stream into the macroblock layer of the H.263 stream. In an imaging system with a processor, A first function of interpreting header information of the MPEG-2 stream to delete a sequence layer and a video group (GOP) layer; And For the remaining images of the MPEG-2 stream, hierarchical information is generated, and the compressed video of the MPEG-2 stream is compressed video of the H.263 stream in a variable length code indicating a specific parameter value required for each layer. Function to convert to A computer-readable recording medium having recorded thereon a program for realizing this.