JP2007201721A - Coded data generating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coded data generating apparatus capable of accurately detecting the presence of an error at decoding of coded data by detecting a syntax and semantic error of the coded data. <P>SOLUTION: An error detection section 100 checks a flag for denoting the presence of errors included in the coded data so as to detect whether or not the errors exist in the coded data and outputs detected information 20 such as error presence information, error presence location and range information, and type information for denoting a coded type at an error presence location. A replacement information generating section 200 generates replacement information 30 on the basis of a replacement code sequence for error correction and the detected information. The replacement code sequence includes a value of resetting the flag indicating the error presence (setting zero to the flag). A bit stream replacement section 300 applies error correction to the coded data on the basis of the replacement information to produce a bit stream 50 without errors wherein zero is set to the flag. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an encoded data generation apparatus that detects an error in encoded data encoded using motion compensated prediction and generates encoded data based on an error detection result.

  When a moving image signal is transmitted or stored, it is often compressed and encoded for efficiency to obtain a compressed moving image signal (hereinafter referred to as a bit stream). As a moving picture compression encoding system, an MPEG (Moving Picture Experts Group, hereinafter referred to as MPEG) system has been standardized and widely used. As described above, it is very important for the efficient use of a transmission system or a storage system to compress a moving image signal by a method such as MPEG and handle it as a bit stream.

  By the way, if a syntax (encoded data string rule) error occurs in compressed encoded data that has been compression-encoded according to an encoding standard with compression as described above, compressed encoded data in which a syntax error has occurred. Compressed encoded data that follows can not be decoded by a decoder that does not have a function capable of avoiding errors. Here, the syntax error is an error in which parsing (decomposing syntax elements) of compressed encoded data cannot be continued.

  For example, in MPEG or the like, a syntax error is detected when a value that is not in the VLC (Variable Length Coding) table is detected during the parsing process, or when the number of blocks in the macroblock does not match the specified value. Detected when the number of macroblocks in a picture exceeds a specified value. A syntax error is corrected by an error correction process such as Reed-Solomon when an error is inherent in a compression encoding device, encoding conversion device, or multiplexing device, or an error that occurs during the transmission or storage of compressed encoded data This may occur when it is not possible or when packet loss occurs.

  When a syntax error is detected, the compression encoding apparatus performs the following operation in order to continue decoding. Since the synchronization code is inserted in the encoded data with general compression, the operation is such that the data block in which the syntax error is detected is discarded, and the next data block is acquired and decoded. Do. As a processing method when a syntax error occurs as described above, a process called error concealment is performed.

  In addition, in the case of an error in semantics (content semantic content description tool) in compressed encoded data that has been compression-encoded in accordance with an encoding standard with compression as described above, the encoded encoded data cannot be encoded correctly. Generally not possible. In addition, depending on the semantic error, a fatal failure may occur in the decoding device. Semantic error is not an error that occurs in parsing compression-encoded data, but an error that occurs because the value obtained by parsing violates the restriction defined in the standard. For example, in MPEG, which is one of the moving image compression coding standards, there is a semantic error in which a value of a certain syntax element is defined as a fixed value but not a fixed value. In MPEG-4 AVC, which is the latest moving image compression coding standard, restrictions are defined in detail by profile and level. For this reason, there is a semantic error in which compressed encoded data that conforms to the standard in the baseline profile level 2 is in violation of the standard in the baseline profile level 3.

  Semantic errors may occur when encoded by an incorrect interpretation in the compression encoding device and encoding conversion device, and may occur in the process of storing, transmitting, and acquiring compressed encoded data. In addition, when users who are not familiar with profiles and levels of video compression coding standards perform data interoperability among many models, there is a high possibility that semantic errors will occur due to misuse. . In addition, although it is not a semantic error, it may be necessary to limit the encoding standard in the operation of the system. An error that does not satisfy the predetermined encoding condition on the system cannot be handled by the corresponding system. As described above, a process called error concealment is performed as a processing method when a semantic error occurs.

  As a conventional system using such an error concealment technique, the system described in Patent Document 1 below can perform appropriate packet discard compensation according to the nature of an image and improve the image quality of a decoded image. The moving image transmission is realized. In other words, this is a system that detects packet discard of an encoded video packet, generates a decoded signal by concealment by replacing an error signal in the discarded packet with an already decoded image signal. Therefore, in the system described in Patent Document 1, the input is a bit stream that may include an error, and the output is a decoded image signal that has been corrected for the error when a bit stream that includes an error is input.

  As a conventional system using another error concealment technique, the device described in Patent Document 2 below does not require a separate disk device for error correction, and is a disk array device that takes advantage of the characteristics of video data. The video transmission provided is realized. That is, the input video data is divided and stored as a bit stream, and when an error occurs in the input video data bit stream, a concealment bit stream that is highly compressed in advance from the input video data is stored in advance. In this case, the error bit stream of the input video data is replaced by decoding and re-encoding the data bit stream. Therefore, in the apparatus of Patent Document 2, an input is a bit stream in which an error may occur, and an output is a bit stream in which the error is corrected when an error occurs.

  Further, as a conventional system using the error concealment technique, the circuit described in Patent Document 3 below uses a normal line immediately after encoding in a facsimile apparatus that requires encoding conversion in real time. When a code error is detected by a code buffer that can temporarily store the encoded information for one minute, concealment is performed by outputting the encoded information for one normal line in the buffer.

  On the other hand, it is also possible to specify an error in the encoded data. For example, an MPEG-2 TS (Transport Stream) packet shown in FIG. 8 is an example of a case where a flag that clearly indicates an error exists in encoded data. FIG. 8 shows the structure of an MPEG-2 TS packet. The field (2) shown in FIG. 8 (indicated by a circled number in FIG. 8) is called a 1-bit transport error indicator (TEI), and the TEI bit is set to 1. This clearly indicates that this packet contains an error. Detailed description regarding other fields is omitted.

As shown in FIG. 8, a packet structure in which a bit that clearly indicates the presence or absence of a syntax error is transmitted together with encoded data is known in the art. For example, it is also disclosed in Patent Documents 4 and 5 below. Yes.
Japanese Unexamined Patent Publication No. 7-111654 (Abstract) Japanese Patent No. 3482971 (Claims) JP 63-292873 A (Claims) Japanese Patent Laying-Open No. 2004-56169 (FIG. 2, paragraph 0003) Japanese Patent Laying-Open No. 2005-26990 (FIG. 2, paragraphs 0020-0022)

  However, the system or apparatus using the error concealment technique described above has the following problems. Since the moving image transmission system in Patent Document 1 is an image signal obtained by decoding the output after error concealment, the moving image signal cannot be transmitted as a bit stream using a communication path or the like after error correction. Therefore, a decoder that does not have an error concealment function cannot correctly reproduce a bitstream having an error.

  In the video transmission device in Patent Document 2, the output is a bit stream of input video data that has been error concealed, but a bit stream for concealment is prepared in advance in a storage medium for each bit stream of the input video data. This is applicable when the bit stream for concealment increases with the increase of the bit stream of the input video data, and because the storage medium is used, any bit stream is transmitted using a communication channel. I can't. In the error replacement circuit of the facsimile in Patent Document 3, the previous one normal line is stored as coding information for concealment. However, in the compression coded bit stream of a moving image using motion compensation predictive coding, If the concealment is performed only with the encoded information, the quality of the reproduced image is greatly deteriorated.

  On the other hand, when an uncorrectable error is detected when receiving the MPEG-2 TS packet, the presence of the error is clearly indicated by setting the TEI bit flag of the MPEG-2 TS packet (indicating the presence of the error). It is possible. Thereby, it is possible to detect that the flag is set at the time of decoding of the MPEG-2 TS packet and perform processing in which the presence of an error is recognized in advance.

  However, error processing at the time of decoding is arbitrary, that is, processing for an error may not be performed at the time of decoding. As described above, when processing for an error is not performed at the time of decoding, the video and audio reproduced after decoding are disturbed, and thus the reproduction is not performed correctly.

  Furthermore, even when an error exists in the MPEG-2 TS packet, the process for setting the TEI bit flag is arbitrary. Therefore, the TEI bit flag may be set to 0 even though an error exists. In such a case, the presence of an error cannot be recognized in advance at the time of decoding, and in this case as well, the video and audio played back after decoding will be disturbed and will not be played back correctly.

  In view of the problems of the conventional example described above, the present invention detects syntax errors and / or semantic errors of encoded data encoded using motion compensated prediction, and the presence of an error when decoding the encoded data. It is an object of the present invention to provide an encoded data generation apparatus that can accurately detect the presence or absence of the data.

In order to achieve the above object, according to the present invention, encoded data encoded using motion compensation prediction is input, and a flag for indicating the presence of an error set in the input encoded data is checked. Detecting whether or not the error exists, the presence information of the error, first position information indicating a position where the error exists, first range information indicating a range where the error exists, and An error detection unit that outputs at least one of classification information indicating an encoding type at a position where an error exists as error detection information;
Based on the error detection information, a replacement code string for correcting the error and generating a replacement code string for replacing the flag of the encoded data with information clearly indicating that the error does not exist is generated. Second position information indicating a position where the encoded data is to be replaced and second range information indicating a range where the encoded data is to be replaced based on the generated replacement code string and the error detection information. A replacement information generating unit that generates replacement information by adding the replacement code string to the generated second position information and second range information;
Based on the replacement information of the replacement information generation unit, the encoded data is replaced with the encoded data in which the detected error is corrected and the information indicating that the error does not exist is set in the flag. A replacement part to be
An encoded data generation apparatus is provided.

In order to achieve the above object, the present invention receives encoded data encoded using motion compensated prediction, detects an error set in the input encoded data, and An error detection unit that checks a flag for indicating the presence or absence of an error set in the data, and outputs the error presence information and the flag setting information as error detection information;
Based on the error detection information, when the error is detected in the encoded data in which the flag in which the error does not exist is set is set, the error is set to the flag of the encoded data. A replacement information generation unit that generates a replacement code string for replacement with information that clearly indicates that it exists;
A replacement unit that replaces the flag of the encoded data with the replacement code string generated by the replacement information generation unit, and generates encoded data in which the information indicating that the error exists is set in the flag And
An encoded data generation apparatus is provided.

  The present invention has the above-described configuration, and can accurately detect the presence or absence of an error when decoding encoded data encoded using motion compensated prediction. Disturbance can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment>
First, a first embodiment of the present invention will be described. FIG. 1 is a block diagram showing a transmission system in which a repeater is used as an encoded data generation apparatus according to an embodiment of the present invention. The transmission system of FIG. 1 shows a connection example of a bit stream generation device 500, an encoded data relay device 600 according to the present invention, and a playback device 700 that is a relay destination. The transmission system illustrated in FIG. 1 has a configuration common to the first to fourth embodiments of the present invention.

  The bit stream generation device 500 is configured to convert image information in the storage medium 510 into an encoded bit stream by the encoder 520 and transmit the image information to the transmission line 1001 by the transmitter 530.

  In addition, when there is an error in the bitstream received from the bitstream generation apparatus 500 via the transmission path 1001, the encoded data relay device 600 corrects the bitstream with the relay device 610 and transmits the corrected bitstream. It is configured to transmit to the reproduction apparatus 700 as a relay destination via a path 1002.

  Also, the playback device 700 that is a relay destination is configured to receive a bit stream transmitted from the encoded data relay device 600 via the transmission path 1002 by the receiver 710 and decode it by the decoder 720.

  In this path, assuming that the bit stream transmitted from the transmitter 530 has an error due to the influence of the transmission path 1001, the repeater 610 according to the present invention can verify and correct the error. Even in a decoder 720 that does not have an error concealment capability for a bitstream having an error, the bitstream can be reproduced. In addition, it is not necessary to prepare error correction information based on the input bitstream in advance, syntax error correction is possible without the need for data storage for compression coding concealment, and compression coding is also possible. A transmission system that performs error correction of a bitstream can be realized.

  The repeater 610 includes one or both of a syntax error correction unit and a semantic error correction unit. Hereinafter, syntax errors and / or semantic errors are simply referred to as errors. Further, the syntax error correction unit and / or the semantic error correction unit included in the repeater 610 will be simply referred to as an error correction unit.

  FIG. 2 shows a block diagram of the error correction unit in the first embodiment of the present invention. As shown in FIG. 2, the error correction unit includes an error detection unit 100, a decoding unit 400, a replacement information generation unit 200, and a bitstream replacement unit 300. Hereinafter, the compression-encoded bit stream is simply referred to as a bit stream. In FIG. 2, first, the bit stream 10 is input to the error detection unit 100 as an input. The error detection unit 100 detects whether or not an error is included in the bitstream 10 by checking whether or not a flag (for example, a TEI bit flag) for indicating the presence of an error is set. Presence / absence, error occurrence position, etc. are output as detection information 20.

  Similarly, the input bitstream 10 is also supplied to the decoding unit 400. The decoding unit 400 decodes the input bitstream 10, outputs header information generated at the time of decoding as an encoding parameter 60, and outputs an image configured by decoding as a decoded image 70. The encoding parameter 60 and the decoded image 70 output from the decoding unit 400 are supplied to the replacement information generating unit 200. The detection information 20 passed from the error detection unit 100 to the decoding unit 400 is also supplied to the replacement information generation unit 200.

  The replacement information generation unit 200 selects a replacement code string for correcting an error in the input bitstream 10 from several code strings prepared in advance based on the detection information 20 supplied from the decoding unit 400. To do. Then, the replacement information generation unit 200 determines the position, range, and replacement code string of the input bitstream 10 to be replaced based on the selected replacement code string and the detection information 20, and uses these pieces of information as replacement information 30. Output. However, the replacement information 30 may be obtained by some external input 40.

  At this time, in the replacement information 30 for correcting the error, the position information and replacement for lowering the bit of the flag position for indicating the presence of the error (that is, for example, setting the bit corresponding to the position of the TEI to 0) A code string is included. It is desirable that the flag position bit for indicating the presence of an error in the replacement code string is set in advance to a value indicating that no error exists.

  Based on the input bitstream 10 supplied from the error detection unit 100 and the replacement information 30 supplied from the replacement information generation unit 200, the bitstream replacement unit 300 converts the code sequence in which an error is detected into a replacement code sequence. By performing the replacement, an error-free bit stream 50 is output. The bit stream 50 without error is subjected to code replacement so that the flag for indicating the presence of the error is cleared by the replacement information 30 described above, and as a result, it is clearly indicated that there is no error in the bit stream 50. Indicated.

  Next, the operation of the error detection unit 100 illustrated in FIG. 2 will be described in detail with reference to FIG. FIG. 3 is a flowchart showing an example of the operation of the error detection unit in the first embodiment of the present invention. In addition to the processing in the error detection unit 100, the flowchart illustrated in FIG. 3 schematically illustrates information output after processing.

  In FIG. 3, the error detection unit 100 first detects an error in the input bitstream 10 while parsing the input bitstream 10 (step S10) (step S11). At this time, the error detection unit 100 checks a flag for indicating the presence of an error included in the input bitstream 10.

  In the error detection determination (step S12), when the input bitstream 10 includes an error (that is, when a flag indicating the presence of the error included in the input bitstream 10 is set), an error exists. If the flag indicating the above and the position information of the bitstream 10 in which an error has occurred, or processing that can parse the bitstream from the reverse, such as Reversible VLC, range information in which a syntax error has occurred, for example, According to the MPEG-4 AVC standard, type information indicating encoding types such as syntax error occurrence, intra prediction, and inter prediction in units of access units, slices, and macroblocks is generated (step S13). (Step S15).

  On the other hand, when the input bitstream 10 does not include an error (that is, when a flag indicating the presence of an error included in the input bitstream 10 is down), a flag indicating that no error exists (error non-existence flag) ) Is generated (step S14), and this error non-existence flag is output as detection information 20 (step S15).

  In step S11 and step S12, for example, when several macroblocks are continuously missing, the number of macroblocks with respect to the picture size is fixed. If the numbers do not match, it is determined that there is a syntax error. Therefore, the detection information 20 in this case includes type information indicating that an error has occurred in the macroblock, position information where the macroblock is missing (that is, an address where the error occurred, a bit stream such as Reversible VLC). If processing that can be parsed from the reverse is used, the address information of the missing macroblock address is obtained.

  Also, for example, in the MPEG-4 AVC encoding method, if the profile value of the sequence parameter set of the stream including B-Slice is a value indicating Baseline Profile, a semantic error occurs, and the unit of the sequence parameter set is the type. It becomes information, and the address where the sequence parameter set exists becomes position information. For example, when the motion vector exceeds a value restricted by the level of the encoding method, the unit of the motion vector becomes type information, and the macro block address where the motion vector exists becomes position information.

  Next, the operation of the decoding unit 400 illustrated in FIG. 2 will be described in detail with reference to FIG. FIG. 4 is a flowchart showing an example of the operation of the decoding unit in the first embodiment of the present invention. Note that the flowchart illustrated in FIG. 4 schematically illustrates information output after processing in addition to the processing in the decoding unit 400.

  In FIG. 4, the decoding unit 400 first decodes the input bitstream 10 (step S40). At this time, it is determined whether or not the decoded image 70 can be generated from the error occurrence position information, the range information, and the type information of the detection information 20 (step S41). If the decoded image 70 cannot be generated due to the occurrence of an error, error concealment is performed for the location where the error has occurred (step S44). Error concealment is performed by interpolating the missing pixel using the pixel values of the surrounding image. For example, if a macroblock is missing, error concealment is performed using a method of interpolation from pixel values around the macroblock. If missing in units of access units, Error concealment is performed using a method such as interpolation using a duplicate image. And the decoding part 400 produces | generates the image in which the error concealment was performed as the decoded image 70 (step S43). In addition, when a decoded image can be generated, the decoded image 70 is output to the replacement information generation unit 200.

  On the other hand, the decoding unit 400 can generate not only the decoded image 70 but also an encoding parameter 60 generated at the time of decoding as additional information in a portion having no error (step S42). Examples of the encoding parameter 60 generated at the time of decoding include information that can be used for simplification of re-encoding, such as sequence and picture header information, motion vectors, and macroblock types. The encoding parameter 60 and the decoded image 70 output from the decoding unit 400 are output to the replacement information generating unit 200. Although not shown in FIG. 4, the decoding unit 400 performs an operation of supplying the detection information 20 supplied from the error detection unit 100 to the replacement information generation unit 200.

  Next, the operation of the replacement information generation unit 200 illustrated in FIG. 2 will be described in detail with reference to FIG. FIG. 5 is a flowchart showing an example of the operation of the replacement information generation unit in the first embodiment of the present invention. In addition to the processing in the replacement information generation unit 200, the flowchart illustrated in FIG. 5 also schematically illustrates information output after processing.

  Based on the detection information 20, the replacement information generation unit 200 performs re-encoding using the decoded image 70 when the above-described encoding parameter 60 is not used (step S51). On the other hand, when the encoding parameter 60 is used, the replacement information generating unit 200 generates a re-encoding parameter based on the encoding parameter 60 (step S50). The re-encoding parameter here is a position or range of the decoded image 70 to be re-encoded. In order to simplify the re-encoding of the decoded image 70 without error, when the encoding parameter 60 such as header information and motion vector is used, based on the encoding parameter 60 output from the decoding unit 400. It is also possible to obtain a re-encoding parameter and use this re-encoding parameter. Then, the replacement information generation unit 200 re-encodes the decoded image 70 of the input bitstream 10 using the re-encoding parameter (Step S51). Note that the re-encoding parameter may be determined by the external input 40.

  In addition to the bitstream re-encoded as described above, the replacement information generation unit 200 sets a value for lowering a flag indicating the presence of an error as a replacement code string, and the replacement code string and the detection information 20 Then, the replacement information 30 including the position information and range information of the input bitstream 10 to be replaced is generated (step S52).

  As described above, according to the first embodiment of the present invention, when a flag for indicating an error included in a motion-coded bitstream that has been predicted for motion compensation is set, a decoded image Since re-encoding is performed using, motion-compensated prediction of a portion where a syntax error has occurred can be recalculated. Therefore, compared to a method in which a replacement code string is prepared in advance or a method in which error concealment is performed by simply copying the previous normal code string, the quality of the reproduced image of the bitstream after error concealment is improved. It is possible to improve. In addition, the replacement code string used when correcting the error of the encoded bitstream is set to lower (set to 0) a flag (for example, a TEI bit flag) indicating the presence of the error. By correcting the error using the replacement code string, it is possible to explicitly indicate that there is no error and to prevent video and audio disturbance due to the occurrence of an error during decoding.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. FIG. 6 is a block diagram of an error correction unit according to the second embodiment of the present invention. As shown in FIG. 6, the error correction unit in the second exemplary embodiment of the present invention includes an error detection unit 100, a replacement information generation unit 201, and a bitstream replacement unit 300. The bitstream replacement unit 300 is the same as the bitstream replacement unit 300 (shown in FIG. 2) in the first embodiment in terms of operation and connection relationship.

  The operation of the error detection unit 100 shown in FIG. 6 is the same as that of the error detection unit (shown in FIGS. 2 and 3) in the first embodiment, but the detection information 20 is sent to the replacement information generation unit 201. It is different in point.

  First, the overall operation of the error correction unit shown in FIG. 6 will be described. In FIG. 6, an input bit stream 10 is input to the error detection unit 100 as an input. The error detection unit 100 detects whether or not an error is included in the bitstream 10 by checking whether or not a flag (for example, a TEI bit flag) for indicating the presence of an error is set. The presence / absence, error occurrence position, and the like are output to the replacement information generation unit 201 as detection information 20.

  Based on the detection information 20 supplied from the error detection unit 100, the replacement information generation unit 201 selects a replacement code string for correcting an error in the input bitstream 10 from several code strings prepared in advance. select. Then, the replacement information generation unit 201 determines the position, range, and replacement code string of the input bitstream 10 to be replaced based on the selected replacement code string and the detection information 20, and uses these pieces of information as replacement information 30. Output. However, the replacement information 30 may be obtained by some external input 40.

  At this time, in the replacement information 30 for correcting the error, the bit of the flag position for indicating the presence of the error is lowered (that is, the position of the TEI, for example) as in the first embodiment of the present invention described above. Position information and a replacement code string are included. It is desirable that the flag position bit for indicating the presence of an error in the replacement code string is set in advance to a value indicating that no error exists.

  Based on the input bitstream 10 supplied from the error detection unit 100 and the replacement information 30 supplied from the replacement information generation unit 201, the bitstream replacement unit 300 converts the code sequence in which an error is detected into a replacement code sequence. By performing the replacement, an error-free bit stream 50 is output. The bit stream 50 without error is subjected to code replacement so that the flag for indicating the presence of the error is cleared by the replacement information 30 described above, and as a result, it is clearly indicated that there is no error in the bit stream 50. Indicated.

  Next, the operation of the replacement information generation unit 201 illustrated in FIG. 6 will be described in detail with reference to FIG. FIG. 7 is a flowchart showing an example of the operation of the replacement information generation unit in the second embodiment of the present invention. In addition to the processing in the replacement information generation unit 201, the flowchart illustrated in FIG. 7 schematically illustrates information output after processing.

  Based on the detection information 20 received from the error detection unit 100, the replacement information generation unit 201 uses a code string prepared in advance according to the type and position of the syntax error occurring in the input bitstream 10 for replacement. A replacement code string is selected (step S20). Then, the replacement information generation unit 201 determines a position and a range where the input bitstream 10 should be replaced based on the selected replacement code string and the detection information 20, and adds an error to the selected replacement code string. The information combined with the value for lowering the flag for indicating the presence of is generated as replacement information 30 (step S21).

  For example, the type information of the detection information 20 is a macro block, some macro blocks are missing, the macro block type before and after the missing macro block is Not Coded, and dmv (differential motion vector) is 0. In this case, the macroblock type of the missing part is similarly determined as Not Coded and dmv is 0, and becomes a replacement code string of the macroblock in which the flag indicating Not Coded of the prepared macroblock is missing. In this case, the replacement information generation unit 201 generates the number of macroblocks with missing replacement code strings as replacement information 30.

  Further, for example, when the type information of the detection information 20 is an access unit and some access units are missing, a replacement code string of the access unit lacking the NoMC / Not Coded flag is obtained. In this case, the replacement information generation unit 201 generates the number of missing access units in the replacement code string as replacement information 30. In addition, in order to match the code amount of the input bitstream 10, a stuffing byte can be added to the replacement code string of the replacement information 30.

  For example, in the MPEG-4 AVC encoding method, when the profile value of the sequence parameter set of the stream including B-Slice is a value indicating Baseline Profile, the replacement information generation unit 201 sets the replacement code string. Is selected as a replacement code string of the replacement information 30. In addition, in order to match the code amount of the input bitstream 10, a stuffing byte can be added to the replacement code string of the replacement information 30.

  Further, a method is conceivable in which the error detection unit 100 does not detect a semantic error and always replaces the same syntax of the input bitstream 10 by using the same code string in the replacement information generation unit 201. For example, it is assumed that the decoder on the receiving side has a restriction that a bit stream having a level value higher than a certain level is not reproduced by looking at the level value in the header of the bit stream. However, it is assumed that the above decoder has the capability of reproducing an image size that can be originally reproduced only at a certain level value or more according to the coding standard. At this time, if only the level value is always rewritten to a certain level or less, the bit stream can be reproduced by the decoder. Therefore, when the error detection unit 100 does not detect a semantic error, the replacement information generation unit 201 prepares a level value supported by this decoder as a replacement code string, and the input bitstream 10 is input. In addition, the bit stream can be reproduced by the decoder just by replacing the level value of the header of the input bit stream 10 with the code string of the prepared level value.

  Here, the replacement information generation unit 201 may select a replacement code string supplied from the external input 40 in selecting a replacement code string. By controlling with the external input 40 in this way, it is possible to prevent an unintended reproduced image from being output.

  As described above, according to the second embodiment of the present invention, when a flag for indicating an error included in a motion-coded video stream that has been predicted for motion compensation is set, an error is set in advance. By preparing a code string for substituting, a higher-speed error concealment process can be realized compared to the case of re-encoding the decoded image for error concealment. In addition, compared with the case where the previous normal code string is simply used as the code string for concealment, the quality of the reproduced image can be improved in the bit stream after the error concealment. In addition, the replacement code string used when correcting the error of the encoded bitstream is set to lower (set to 0) a flag (for example, a TEI bit flag) indicating the presence of the error. By correcting the error using the replacement code string, it is possible to explicitly indicate that there is no error and to prevent video and audio disturbance due to the occurrence of an error during decoding.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. In the first and second embodiments of the present invention described above, an error is detected by checking a flag for indicating the presence of an error. If an error exists, the error is corrected and a replacement character string is used. The flag for indicating the presence of an error is lowered by means of this, so that processing that recognizes the presence of an error in advance can be performed at the time of decoding. However, since the process for setting a flag is arbitrary, this flag is not always set when an error occurs.

  Therefore, in the third embodiment of the present invention, the error detection unit 100 performs error detection processing on the input bitstream (corresponding to step S11 in FIG. 3), and the presence / absence of an error, error position information, and range information. Is generated, and if an error exists, a replacement code that sets (sets to 1) a flag (for example, a TEI bit flag) to indicate the presence of an error in the input bitstream 10 A bit stream 50 is generated by performing a code replacement process according to the sequence.

  As a result, an error in the input bitstream 10 is not corrected, but a flag for explicitly indicating the presence of an error is set at an error occurrence location that does not indicate that an error exists. When decoding the output bitstream 50, it is possible to recognize in advance and accurately the presence or absence of an error and the location of the error, and prevent video and audio disturbance due to the occurrence of an error during decoding. Is possible.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described. In the fourth embodiment of the present invention, in the semantic error detection in the first to third embodiments of the present invention, for example, a restriction is imposed on the coding conditions of the standardized coding standard in system operation. Applicable to the case. For example, the error detection unit 100 operates as a restriction semantic error detection part, and detects whether or not a certain system restriction is satisfied for an input bitstream. When the system restrictions are not satisfied, the error detection unit 100 outputs the detection information 20 similar to that in the first to third embodiments of the present invention described above. Regarding the subsequent operation, the error is read as an error that does not satisfy the predetermined encoding condition, and the same operation as in the first to third embodiments of the present invention described above is performed.

  Further, in the fourth embodiment of the present invention, even if the standardized encoding method is satisfied, the standard is not satisfied by adding a finer restriction to the restriction of the encoding method for operational reasons. Bitstreams with errors can be corrected. For example, a bit stream that satisfies the MPEG-2 standard but does not satisfy the reserved bit value of the MPEG-2 bit stream restricted by a certain system cannot be handled by the corresponding system. According to the fourth embodiment, since the reserved bit value in the bit stream is corrected so as to satisfy the restrictions of the corresponding system, a bit stream that can be handled by the corresponding system can be generated.

  Further, for example, it is assumed that there is a bit stream encoded by Open GOP that satisfies the MPEG-2 standard. On the other hand, it is assumed that there is a restriction that an MPEG-2 bit stream that is restricted in a certain system must be encoded with a Closed GOP. In this case, it cannot be reproduced by the decoder of the corresponding system. However, according to the fourth embodiment of the present invention, the MPEG-2 GOP is encoded so as to satisfy the restrictions of the corresponding system. In order, the first B-picture immediately after I-picture is changed from bidirectional prediction to unidirectional prediction and re-encoded. Thus, since the generated bit stream satisfies the Closed GOP, it is possible to generate a bit stream that can be reproduced by the decoder of the corresponding system.

  The present invention makes it possible to accurately detect the presence / absence of an error when decoding encoded data encoded using motion compensated prediction, and to prevent video and audio disturbance due to the occurrence of an error. And is applicable to a coded data processing technique for detecting coded data error encoded using motion compensation prediction and generating coded data based on the error detection result. .

It is a block diagram which shows the transmission system in which a repeater is used as the encoded data generation apparatus which concerns on embodiment of this invention. It is a block diagram which shows the structural example of the error correction part in the 1st Embodiment of this invention. It is a flowchart which shows an example of operation | movement of the error detection part in the 1st Embodiment of this invention. It is a flowchart which shows an example of operation | movement of the decoding part in the 1st Embodiment of this invention. It is a flowchart which shows an example of operation | movement of the replacement information generation part in the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the error correction part in the 2nd Embodiment of this invention. It is a flowchart which shows an example of operation | movement of the replacement information generation part in the 2nd Embodiment of this invention. It is a figure which shows the structure of the MPEG-2 TS packet in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Error detection part 200, 201 Replacement information generation part 300 Bit stream replacement part 400 Decoding part 500 Bit stream generation apparatus 510 Storage medium 520 Encoder 530 Transmitter 600 Encoded data repeater 610 Repeater 700 Reproducing apparatus 710 Receiver 720 Decoder 1001, 1002 Transmission path

Claims (2)

Encoded data encoded using motion compensated prediction is input, and a flag for indicating the presence of an error set in the input encoded data is checked to determine whether the error exists. And detecting the presence information of the error, the first position information indicating the position where the error exists, the first range information indicating the range where the error exists, and the encoding type at the position where the error exists. An error detection unit that outputs at least one of the type information shown as error detection information;
Based on the error detection information, a replacement code string for correcting the error and generating a replacement code string for replacing the flag of the encoded data with information clearly indicating that the error does not exist is generated. Second position information indicating a position where the encoded data is to be replaced and second range information indicating a range where the encoded data is to be replaced based on the generated replacement code string and the error detection information. A replacement information generating unit that generates replacement information by adding the replacement code string to the generated second position information and second range information;
Based on the replacement information of the replacement information generation unit, the encoded data is replaced with the encoded data in which the detected error is corrected and the information indicating that the error does not exist is set in the flag. A replacement part to be
A coded data generation apparatus having the same. Encoded data encoded using motion compensated prediction is input, an error set in the input encoded data is detected, and the presence / absence of an error set in the encoded data is detected. An error detection unit that checks a flag for indicating and outputs the error presence information and the flag setting information as error detection information;
Based on the error detection information, when the error is detected in the encoded data in which the flag in which the error does not exist is set is set, the error is set to the flag of the encoded data. A replacement information generation unit that generates a replacement code string for replacement with information that clearly indicates that it exists;
A replacement unit that replaces the flag of the encoded data with the replacement code string generated by the replacement information generation unit, and generates encoded data in which the information indicating that the error exists is set in the flag And
A coded data generation apparatus having the same.

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