Partial Video Decoding Method, Device and System

Abstract

Encoded video data representing partial video images is decoded from a first video stream such as a HEVC bitstream. The first video stream comprises video images divided into a spatial array of independently decodable slices. The first video stream comprises network abstraction layer units that each contain video content data for a respective one of the slices preceded by a header that comprises parameters relating to the respective one of the slices in relation to the first video stream. Previously prepared information such as meta data about positions of parameters in the network abstraction layer units or a plurality of different versions of the network abstraction layer units for different partial image sizes (different picture sizes) is used. The meta data may be used for partially rewriting the network abstraction layer units for a sub-array of slices, the network abstraction layer units being rewritten at a location selected on the basis of meta data, to make the network abstraction layer units consistent with a second video stream of encoded video data only for the sub-array of slices. Versions of the network abstraction layer units may be selected for the sub-array of slices, from the plurality of different versions. Subsequently, the partial video images are generated by decoding the encoded video data from the rewritten network abstraction layer units.

What is claimed is: 
     
         1 . A video stream source system, comprising a storage system, a transmission interface and a controller, the controller being configured to:
 receive a first indication of a selection of a sub-array of a spatial array of independently decodable slices in a first video stream that encodes full video images divided into the spatial array, the first video stream comprising network abstraction layer units that each contain video data for a respective slice preceded by a header that comprises parameters relating to the respective slice in relation to the first video stream; and   cause network abstraction layer units for the selected sub-array in the first video stream to be retrieved from the storage system and to be transmitted via the transmission interface.   
     
     
         2 . A video stream source system according to  claim 1 , wherein the controller is configured to:
 receive a second indication of a selection of a new sub-array of a spatial array;   cause network abstraction layer units for the selected new sub-array in the first video stream to be retrieved from the storage system and to be transmitted via the transmission interface, using network abstraction layer units from a first and second version of the first video stream for slices within and outside an overlap between the previous sub-array and the new sub-array respectively, the first version comprising inter frame relation based image data and the second version comprising only data encoded independent of inter frame relations, until a frame wherein the first version comprises image data encoded independent of inter frame relations; and   subsequently cause network abstraction layer units comprising image data from the first version for all slices within the new sub-array to be retrieved from the storage system and to be transmitted via the transmission interface.   
     
     
         3 . A decoding system for decoding partial video images from a first video stream that encodes full video images divided into a spatial array of independently decodable slices, wherein the first video stream comprises network abstraction layer units that each contain video content data for a respective one of the slices preceded by a header that comprises parameters relating to the respective one of the slices in relation to the first video stream, and wherein information defining versions of network abstraction layer units corresponding to derived streams with differently sized images are provided, the decoding system comprising:
 a storage system;   a controller, configured to indicate a selection of a sub-array of a spatial array of independently decodable slices in the first video stream;   a stream generator, configured to retrieve the information defining versions of the network abstraction layer units from the storage system and to obtain the versions of the network abstraction layer units with video content data corresponding to the first video stream and headers for network abstraction layer units of a second video stream with an image size corresponding to the selected sub-array, based on the retrieved information; and   a decoder, with an input coupled to a stream pre-processor, and configured to decode partial video images containing only video data from the sub-array, from the obtained versions of the network abstraction layer units.   
     
     
         4 . A decoding system according to  claim 3 , wherein the information defining versions of network abstraction layer units comprises stored versions of the headers with field sizes for indicating the spatial location of the slices in a plurality of different image sizes. 
     
     
         5 . A decoding system according to  claim 3 , comprising:
 a stream pre-processor, coupled between the stream generator and the decoder, configured to receive the obtained versions of the network abstraction layer units from the stream generator and to modify the obtained versions of the network abstraction layer units by replacing values of the indications of the spatial location of the slices in the network abstraction layer units, using values of the indications of the spatial location of the slices from a predetermined set of shortened values of the indications of the spatial location of the slices that is independent of a location of the sub-array within the full video images.