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• • H—ELECTRICITY
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  • H04N7/17318—Direct or substantially direct transmission and handling of requests

Definitions

• the present invention relates to a method and apparatus for encoding and transmitting a video signal according to a scalable scheme, a method and apparatus for decoding such an encoded data stream, and the encoded data stream.
• Scalable Video Codec is a method which encodes video into a sequence of pictures with the highest image quality while ensuring that part of the encoded picture sequence (specifically, a partial sequence of frames intermittently selected from the total sequence of frames) can be decoded to represent the video with a lower image quality.
• Motion Compensated Temporal Filtering MCTF is an encoding scheme that has been suggested for use in the scalable video codec.
• One solution to this problem is to hierarchically and additionally provide an auxiliary picture sequence for low bitrates, for example, a sequence of pictures that have a small screen size and/or a low frame rate.
• One example is to encode and transmit 4CIF (Common Intermediate Format) , CIF, and QCIF (Quarter CIF) picture sequences of a video signal to a decoding apparatus as shown in Fig. 1.
• Such picture sequences have redundancy since the same video signal source is encoded into the sequences.
• one method entails inter-sequence prediction of video frames in a higher sequence from video frames in a lower sequence temporally coincident with the video frames in the higher sequence, so as to reduce the amount of coded information of the higher sequence, as illustrated in Fig. 1.
• the original or base layer of a lower sequence may be used to predictively encode an original or base layer of a higher sequence.
• the resulting encoded sequence is referred to as a base or original layer.
• the quantization causes an information loss in the base or original layer.
• the encoder 20 k of each sequence performs inverse quantization 201 k and inverse transformation 202 k to reconstitute the sequence prior to DCT and quantization.
• a difference is then obtained between the actual sequence prior to DCT and quantization and the reconstituted sequence. This difference represents data lost during the DCT and quantization process.
• the residual sequence layer data may undergo the same process to produce a higher level of SNR enhancement layer data, and higher levels of SNR enhancement layer data may also undergo the same process to obtain still higher levels of residual sequence layer data.
• the various levels of SNR enhancement data will be collectively referred to as SNR enhancement layer data or residual sequence layer data.
• the SNR enhancement layer data is provided such that the image quality can be gradually improved by increasing the decoding level of the SNR enhancement layer data, which is referred to as Fine Grained Scalability. Namely, the more levels of residual sequence layer data that are decoded and added to the associated base layer, the higher the quality of the resulting image. Because the number of levels of SNR enhancement layer data is controllable or selectable, these fine grain improvements in quality are scalable; hence the name, Fine Grained Scalability or FGS .
• an extractor 22 transmits a stream selected depending on transmission channel bandwidth and the type of a sequence currently requested by the decoding apparatus. For example, as shown in Fig. 3, when the decoding apparatus currently requests a CIF sequence and the transmission channel bandwidth permits, data 301 of an SNR base layer of a QCIF sequence, data 302 of an SNR base layer of a CIF sequence, data 303 of an SNR enhancement layer of the QCIF sequence, and data 304 of an SNR enhancement layer of the CIF sequence are, in the named order, extracted in specific units from a storage unit 21 and a data stream including such extracted data is then transmitted.
• the enhancement layers of the sequences are transmitted after all the base layers of the sequences are transmitted, and the sequences in each layer are transmitted in increasing order of their transfer rates. If the transmission channel bandwidth is reduced during transmission, the extractor 22 transmits only up to a transmittable bit, thereby failing to transmit the subsequent bitstream in each transmission segment 310. For example, in the case of Fig. 3, part of the data bitstream, starting from high-precision error compensation data part (i.e. , the LSB of the error compensation data) of the SNR enhancement layer of the CIF sequence, is not transmitted.
• the above method which sequentially transmits sequences in increasing order of their transfer rates, may unnecessarily occupy the transmission channel due to transmission of unnecessary data, which is not used by the decoding apparatus.
• the decoding apparatus decodes only the CIF sequence to display video to the user in the example of Fig. 3, the SNR enhancement layer data of the QCIF sequence is transmitted although the SNR enhancement layer data is not used while the SNR base layer data of the QCIF sequence is used for prediction of the SNR base layer frame of the CIF sequence.
• the SNR enhancement layer data of the QCIF sequence is transmitted although it actually makes no contribution to improving the image quality, whereas the amount of transmitted data of the enhancement layer of the CIF sequence is reduced although it directly contributes to improving the image quality.
• the present invention relates to a method and apparatus for encoding, transmitting and decoding a video signal.
• a method of decoding a video signal at least a portion of a picture in a first picture sequence layer is decoded based on a second picture sequence layer if an indicator in the video signal indicates inter-layer prediction coding.
• the second picture sequence layer may have a lower frame rate than the first picture sequence layer, may have a bitrate less than a bitrate of the first picture sequence layer, may have a picture resolution less than the first picture sequence layer, and/or may have a picture display size less than the first frame sequence.
• the picture in the first picture sequence layer is a base picture, where a base picture has a base level of quality for the first picture sequence layer.
• the decoding step may include improving the quality level of the decoded base picture using enhancement layer picture information associated with the base picture.
• a value of the indicator greater than zero indicates inter-layer prediction coding for the base picture.
• a portion of a picture in a first picture sequence layer is decoded based on at least a portion of a second picture sequence layer base picture in a second picture sequence layer and enhancement layer picture information associated with the second picture sequence layer base picture according to a quality level represented by an indicator in the video signal .
• the second picture sequence layer base picture has a base level of quality for the second picture sequence layer, and the enhancement layer picture information associated with the second picture sequence layer base picture provides information to improve the quality level of the second picture sequence layer base picture.
• the second picture sequence layer base picture may be decoded based on the enhancement layer picture information according to the quality level represented by the indicator to produced an enhanced picture, and the portion of the picture in the first picture sequence layer may be decoded based on the enhanced picture.
• a decoder decodes at least a portion of a picture in a first picture sequence layer based on a second picture sequence layer if an indicator in the video signal indicates inter-layer prediction coding.
• At least a portion of a picture in a first picture sequence layer is encoded based on a second picture sequence layer and an indicator in the video signal is set to indicate inter-layer prediction coding of the picture in the first picture sequence layer.
• an encoder encodes at least a portion of a picture in a first picture sequence layer based on a second picture sequence layer and sets an indicator in the video signal to indicate inter-layer prediction coding of the picture in the first picture sequence layer.
• a bitstream representing a video signal has a data structure, includes a first stream portion representing at least a portion of a picture in a first picture sequence layer encoded based on a second picture sequence layer, and includes an indicator to indicate inter-layer prediction coding of the picture in the first picture sequence layer.
• Fig. 1 illustrates an example of sequences having different screen sizes and/or different frame rates into which a video signal is encoded through inter-sequence prediction
• Fig. 2 is a block diagram of an apparatus for encoding the video signal into the sequences as shown in Fig. 1 and transmitting the sequences;
• Fig. 3 illustrates a transmission format of data that the encoding apparatus of Fig. 2 extracts and transmits upon receiving a CIF sequence transmission request from a decoder
• Fig. 4 is a block diagram of an apparatus for encoding a video signal into sequences having different screen sizes and/or different frame rates through inter-sequence prediction of the video signal according to an embodiment of the present invention
• Fig. 5 illustrates sequences encoded by the apparatus of Pig. 4 and a transmission format of data that the apparatus of Pig. 4 ' extracts and transmits from the encoded sequences according to an embodiment of the present invention
• Fig. 6 illustrates a transmission format of data extracted from the encoded sequences according to another embodiment of the present invention.
• Fig. 7 is a block diagram of an apparatus for decoding a data stream encoded by the apparatus of Fig. 4.
• Features, elements, and aspects of the invention that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects in accordance with one or more embodiments.
• Fig. 4 is a block diagram of a video signal encoding apparatus to which an encoding and transmission method according to the present invention is applied.
• the video signal encoding apparatus of Fig. 4 is similar in structure to the apparatus of Fig. 2. However, sequence encoders 40 k and an extractor 42 in the apparatus of Fig. 4 have different features from those of the apparatus of Fig. 2. The video signal encoding apparatus of Fig. 4 will now be described in detail, focusing on the sequence encoders 40 k and the extractor 42.
• Each of the encoders 4O 2 and 4O 3 of lower picture sequences having different picture or display sizes (e.g., different resolution) and/or different frame rates provide not only data of an SNR base layer but also data of an SNR enhancement layer
• each of the encoders 40i and 4O 2 of the higher sequences uses video frames reconstructed by using both the SNR base layer data and the associated SNR enhancement layer data of the lower sequence when performing inter-sequence prediction of video frames present in the sequence produced by each of the encoders 4O 1 and 4O 2 (S500) .
• the level of the SNR enhancement layer data to be used for video reconstruction is determined and set in each encoder 40 k based on conditions, such as an image quality to be provided and a secured transmission channel capacity.
• This level is then indicated by inserting a field or flag prediction_SNR_level inserted in headers (for example, slice or picture headers) of the encoded SNR base layer data stream so that the level value is transferred to a decoder.
• the prediction_SNR_level value indicates the level value.
• the prediction_SNR_level is also set in the extractor 42 of the encoding apparatus of Fig. 4. From each encoded data stream 501 stored in a storage unit 41, the extractor 42 extracts and transmits data for a picture sequence currently requested by a decoding apparatus.
• Fig. 5 shows an arrangement of data units of each data stream segment transmitted when the decoding apparatus requests a CIF sequence and bandwidth required for the transmission channel is available.
• the extractor 42 For CIF sequence transmission, the extractor 42 first arranges a data unit aa of the SNR base layer of its lower (i.e. , QCIF) sequence and subsequently arranges data units ab, ac, ad, ae and af up to the set prediction_SNR_level from among data units ab to ah of the SNR enhancement layer of the QCIF sequence. The extractor 42 subsequently arranges a data unit ba of the SNR base layer of the CIF sequence and data units bb, be, bd, be and bf up to the set prediction_SNR_level from among data units bb to bh of the SNR enhancement layer of the CIF sequence.
• QCIF lower
• the extractor 42 arranges remaining data units ag and ah of the SNR enhancement layer of the QCIF sequence, subsequent to the data units bb to bf, and arranges remaining data units bg and bh of the SNR enhancement layer of the CIF sequence, subsequent to the remaining data units ag and ah, and then transmits the arranged data stream.
• the remaining data units ag and ah of the SNR enhancement layer of the QCIF sequence are not used when the video of the CIF sequence is presented.
• the remaining data units ag and ah of the SNR enhancement layer of the QCIF sequence, which are not used in the prediction operation, are arranged and transmitted in the data stream when the transmission channel bandwidth permits because the user may view video of the QCIF sequence using a device having a low decoding capability such as a mobile phone after storing the data transmitted from the extractor 42.
• the extractor 42 may arrange the remaining data units bg and bh of the SNR enhancement layer of the CIF sequence, subsequent to the data units bb to bf of the SNR enhancement layer of the CIF sequence up to the set prediction_SNR_level . Then the extractor 42 may arrange the remaining data units ag and ah of the SNR enhancement layer of the QCIF sequence at the end of the data stream, and transmit the arranged data stream.
• part of the data stream starting from the SNR enhancement layer data of the QCIF sequence that makes no contribution to improving the image quality of currently decoded video, is not transmitted. If the channel conditions are further deteriorated, part of the data stream is not transmitted in the order from data that slightly increases the SNR of video to data that greatly increases the SNR of video. That is, the image quality of decoded video is resistant to variations in the channel conditions, as compared to the conventional transmission method.
• the prediction_SNR_level is set to zero, SNR enhancement layer data of a lower sequence is not used for prediction of frames of a higher sequence, so that the SNR enhancement layer data of the lower sequence is not transmitted. Accordingly, a non-zero value of the prediction_SNR_level indicates that inter-layer prediction has taken place, while a zero value indicates no inter-layer prediction.
• data of an SNR enhancement layer of a currently selected sequence is arranged and transmitted in a transmission segment and data of an SNR enhancement layer of a lower sequence is subsequently arranged and transmitted in the transmission segment .
• FIG. 6 An example of such a case is illustrated in Fig. 6, in which a CIF sequence is selected so that data of an SNR enhancement layer of a QCIF sequence is not transmitted in a data stream. Even if the data of the SNR enhancement layer of the QCIF sequence is transmitted, it is arranged and transmitted at the end of the data stream (601) .
• Fig. 7 is a block diagram of an embodiment of an apparatus for decoding a data stream encoded and transmitted by the apparatus of Fig. 4.
• the decoding apparatus of Fig. 7 receives a plurality of sequences and decodes a higher sequence into a video signal, and includes a demuxer (or demultiplexer) 70, a main decoder 71, and a sub-decoder 72.
• the demuxer 70 separates a received data stream into a data stream of a main sequence and a data stream of a sub-sequence.
• the main decoder 71 converts the data stream of the separated main sequence (for example, a CIF sequence) back to an original video signal according to an MCTF scheme.
• the sub-decoder 72 decodes the data stream of the separated sub-sequence (for example, a QCIF sequence) according to a specified scheme, for example, according to the MPEG4 or H.264 standard.
• the main decoder 71 reads the prediction_SNR_level described above from a header of the input data stream and notifies the sub-decoder 72 of the prediction_SNR_level .
• the notification of prediction_SNR_level between the decoders is not necessary in an embodiment where the prediction_SNR_level is recorded and transmitted in each of the sequences.
• the sub-decoder 72 When decoding the received data stream of the sub-sequence, the sub-decoder 72 decodes SNR base layer data which may be included, together with the SNR enhancement layer, in the received data stream. Then, the sub-decoder 72 provides the main decoder 71 with frames that are decoded to improve the image quality of video using data up to the notified prediction_SNR_level, from among SNR enhancement layer data included in the received data stream of the sub-sequence.
• the main decoder 71 decodes frames in the received main sequence, for which frames in the sub-sequence are used as their predictive images, into original video signals based on images predicted from frames provided from the sub-decoder 72 or, if needed, from scaled versions of these frames.
• the decoding apparatus described above may be incorporated into a mobile communication terminal, a media player, or the like.
• an apparatus and method for encoding and decoding a video signal performs inter-sequence prediction using video frames reconstructed by additionally using error compensation data (e.g. , SNR enhancement layer data or residual sequence layer data) , thereby improving the image quality relative to the amount of coded data.
• error compensation data e.g. , SNR enhancement layer data or residual sequence layer data
• the apparatus and method also arrange and transmit encoded data units sequentially starting from data units which greatly affect the image quality of a sequence that currently needs to be decoded, thereby making the image quality less sensitive to variations in the channel capacity. Also, the transfer rate may be reduced to more efficiently allocate the transmission channel .

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• Databases & Information Systems (AREA)
• Computer Networks & Wireless Communication (AREA)
• General Engineering & Computer Science (AREA)
• Compression Or Coding Systems Of Tv Signals (AREA)

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• 2005
  • 2005-12-06 WO PCT/KR2005/004147 patent/WO2006062330A1/en active Application Filing
  • 2005-12-06 KR KR1020077012666A patent/KR100880639B1/ko active IP Right Grant
  • 2005-12-06 EP EP05819115A patent/EP1820352A4/en not_active Withdrawn

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