Method and apparatus for predecoding and decoding bitstream including base layer

Abstract

A method and apparatus for extracting a higher quality video stream for a given bit-rate by replacing a specific frame by a base layer frame at a predecoder are provided. A predecoding method performed by the predecoder includes selecting a mode by determining frames to be skipped according to a predetermined criterion among frames located at positions where the base layer exists, and extracting a portion of the bitstream according to the selected mode and extraction conditions.

1 . A method for predecoding a bitstream containing at least one base layer, said method comprising:
 determining at least one frame to be skipped according to a predetermined criterion among frames located at positions where the at least one base layer exists; and   extracting a portion of the bitstream according to the determined at least one frame and at least one extraction condition.   
     
     
         2 . The method of  claim 1 , wherein the predetermined criterion is a transmissible bit-rate determined based on a transmission condition of a network connected to a decoder. 
     
     
         3 . The method of  claim 2 , wherein the determining of the at least one frame to be skipped comprises determining that all the frames located at the positions of the at least one base layer are skipped if the bit-rate is below a first threshold. 
     
     
         4 . The method of  claim 2 , wherein the determining of the at least one frame to be skipped comprises determining that at least one high-pass frame is skipped among the frames located at the positions of the at least one base layer if the bit-rate is between first and second thresholds. 
     
     
         5 . A predecoder for extracting a portion of a bitstream containing at least one base layer, the predecoder comprising:
 a mode selection module which determines at least one frame to be skipped according to a predetermined criterion among frames located at positions where the at least one base layer exists; and   a bitstream extraction module configured to extract a portion of the bitstream according to a selected mode and at least one extraction condition.   
     
     
         6 . The predecoder of  claim 5 , wherein the predetermined criterion is a transmissible bit-rate determined based on a transmission condition of a network connected to a decoder. 
     
     
         7 . The predecoder of  claim 6 , wherein the mode selection module determines to skip all frames located at least one respective position of the at least one base layer if the bit-rate is below a first threshold. 
     
     
         8 . The predecoder of  claim 6 , wherein the mode selection module determines to skip at least one high-pass frame among the frames located at least one respective position of the at least one base layer if the bit-rate is between first and second thresholds. 
     
     
         9 . A recording medium having a computer readable program recorded therein, the program for executing a method for predecoding a bitstream containing at least one base layer, said method comprising:
 determining at least one frame to be skipped according to a predetermined criterion among frames located at positions where the at least one base layer exists; and   extracting a portion of the bitstream according to the determined at least one frame and at least one extraction condition.