Method of switching video sequences and corresponding switching device and decoding system

Abstract

The invention relates to a method of switching from a first to a second video sequence, in which it is provided, in order to avoid the creation of special access points such as splicing points defined in MPEG standard, to insert at the switching point, between the two sequences, an additional sequence of k pictures. These pictures, said minimal in that sense that they are coded with a reduced number of bits, may be for instance uniform color pictures or the repetition of a single previous I or P picture. Application: decoding systems with devices for switching from programs to other ones.

1 . A method of switching from a first video sequence to a second one, both old and new sequences being composed of pictures of type T=I, P or B according to the fact that said pictures are independently coded, or predicted from earlier I or P pictures, or bidirectionally predicted from earlier and later P pictures and/or I pictures, wherein an additional sequence of k pictures is inserted at the switching point between the two sequences, k having a value sufficient in order to have compatible sequences and said additional pictures being coded with a few number of bits.  
     
     
         2 . A method according to  claim 1 , wherein the following steps are successively implemented: 
 (a) the old sequence to be replaced by the new one is cut on a P picture, at a first switching point, and a sequence of k minimal P pictures is then inserted;    (b) after this sequence of additional pictures, at a second switching point said new sequence is inserted.    
     
     
         3 . A method according to  claim 2 , wherein said sequence is a sequence of k uniform colour pictures.  
     
     
         4 . A method according to  claim 2 , wherein said sequence is a sequence of pictures that are copies of a previous I or P picture.  
     
     
         5 . A method according to anyone of  claims 2  to  4 , wherein the following additional steps are implemented after the steps (a) and (b): 
 (c) said second sequence is cut at a third switching point, in order to be replaced by the first one;  
 (d) at said third switching point, additional pictures are similarly inserted until the first old picture to occur is an I picture, the first old sequence being then re-inserted.  
 
     
     
         6 . A method according to anyone of  claims 1  to  5 , wherein, each time a B picture is predicted from a P picture not included in the same group of pictures, the first B pictures of any group of images are replaced by minimal B pictures at transitions.  
     
     
         7 . A method according to anyone of  claims 1  to  6 , wherein said old and new video sequences are bitstreams encoded according to the so-called MPEG-2 standard.  
     
     
         8 . A decoding system for decoding n parallel video bitstreams corresponding to video sequences of pictures said intra if they have been coded without any reference to any other picture or said predicted or interpolated according to the fact that they are predicted by motion-compensated prediction from an earlier intra or predicted picture or bidirectionally interpolated from an earlier and a later picture, said system comprising a switching device that includes in cascade selecting means, for the selection of the bitstream which has to be decoded, and decoding means for decoding said selected bitstream, wherein said selecting means comprise, in view of the implementation of a method according to anyone of  claims 1  to  7 , control means for a selective switchover of the bitstream which has to be decoded.  
     
     
         9 . In a decoding system for decoding n parallel video bitstreams corresponding to video sequences of pictures said intra if they have been coded without any reference to any other picture or said predicted or interpolated according to the fact that they are predicted by motion-compensated prediction from an earlier intra or predicted picture or bidirectionally interpolated from an earlier and a later picture, or in association with such a system, a switching device comprising selecting means provided for a selective switchover of the bitstream which has to be decoded according to a switching method such as described in anyone of  claims 1  to  7 .