Trick play signal generation for a digital video recorder using retrieved intra-encoded pictures and generated inter-encoded pictures

Abstract

The invention relates to the generation of a trick play information stream from a normal play information stream, so that they can be recorded together as a composite information stream on the record carrier, such that upon reproduction in a trick play reproduction mode, an information signal of sufficient quality, eg as regards visibility, can be obtained. One aspect of the invention lies in the generation of GOPs, each GOP comprising an I-frame retrieved from the original normal play information stream, and one or more so-called ‘empty P frames’.(FIG. 12) Another aspect of the invention is the requirement of generating GOPs for the trick play information stream that have a constant bitcost per GOP. Again another aspect of the invention lies in the retrieval of the I-frame for the trick play information stream from the normal play information. More specifically, an I frame is generated by retrieving from an I-frame included in the normal play information, the DC coefficient of the I frame and a number of AC coefficients from that I frame and generate the I-frame for the trick play information stream therefrom. More specifically, the number of AC coefficients for an I-frame of the trick play information signal depends on the difference between the DC coefficients of two subsequent I-frames in the normal play information from which the I-frame to be generated and the just previously generated I-frame for the trick play information signal have been derived.

1 . Apparatus for recording a digital video information signal on a record carrier, the apparatus comprising 
 input means for receiving the digital video information signal,    trick play signal generating means for generating a trick play signal from said digital video information signal, so as to enable a trick play reproduction at a speed m times the nominal reproduction speed, where m is an integer larger than 1,    merging means for merging said digital video information signal and said trick play signal into a composite information signal,    writing means for writing said composite information signal in a track on said record carrier, said trick play signal generating means being adapted to 
 (a) retrieve intra encoded pictures from said digital video information signal,  
 (b) generate inter encoded pictures,  
 (c) merge said intra encoded pictures and said inter encoded pictures, so as to obtain a trick play signal comprising subsequent groups of pictures, comprising an intra encoded picture, followed by a number of n of said generated inter encoded pictures, where n is an integer larger than 0, the generated inter encoded pictures being such that, upon reproduction at said trick play speed, an inter encoded picture following an intra encoded picture results, upon decoding, in a repeated presentation of a picture obtained from decoding said intra encoded picture.  
   
     
     
         2 . Apparatus as claimed in  claim 1 , wherein an inter encoded picture in said group of pictures has been obtained by an encoding step which is equivalent to encoding a picture which is a copy of the previous picture in the said group of pictures that led to the intra encoded picture in said group of pictures.  
     
     
         3 . Apparatus as claimed in  claim 1  or  2 , wherein the apparatus is further adapted to record a second trick play signal on said record carrier, said second trick play signal being meant for a reproduction from said record carrier at a second trick play speed p*m times said nominal reproduction speed, p being a constant larger than 1, said trick play signal generating means further being adapted to generate said second trick play signal from said video information signal by selecting each p-th group of pictures from the first mentioned trick play signal, said merging means being further adapted to merge said second trick play signal into said composite signal.  
     
     
         4 . Apparatus as claimed in  claim 3 , wherein the apparatus is further adapted to record a third trick play signal on said record carrier, said third trick play signal being meant for a reproduction from said record carrier at a third trick play speed p*m*q times said nominal reproduction speed, q being a constant larger than 1, said trick play signal generating means further being adapted to generate said third trick play signal from said video information signal by selecting each q-th group of pictures from the second trick play signal, said merging means being further adapted to merge said third trick play signal into said composite signal.  
     
     
         5 . Apparatus as claimed in  claim 1  or  2 , wherein the apparatus is further adapted to record a second trick play signal on said record carrier, said second trick play signal being meant for a reproduction from said record carrier at a second trick play speed−m times said nominal reproduction speed, said trick play signal generating means further being adapted to generate said second trick play signal from said video information signal by reversing the sequence of pictures in each group of pictures in the first mentioned trick play signal, said merging means being further adapted to merge said second trick play signal into said composite signal.  
     
     
         6 . Apparatus as claimed in  claim 1  or  2 , wherein said trick play signal generating means is adapted to generate said groups of pictures in said trick play signal such that they all have a constant bit cost.  
     
     
         7 . Apparatus as claimed in  claim 1  or  2 , wherein said intra encoded pictures in said trick play signal are data compressed versions of intra encoded pictures comprised in said digital video information signal.  
     
     
         8 . Apparatus as claimed in  claim 7 , wherein said trick play signal generating means is adapted to data compress intra encoded pictures comprised in said digital video information signal by lowering the resolution of said intra encoded pictures so as to obtain said intra encoded pictures of said trick play signal.  
     
     
         9 . Apparatus as claimed in  claim 7 , wherein said trick play signal generating means is adapted to data compress intra encoded pictures comprised in said digital video information signal by selecting a restricted number of AC coefficients of said intra encoded pictures so as to obtain said intra encoded pictures of said trick play signal.  
     
     
         10 . Apparatus as claimed in  claim 9 , wherein the trick play signal generating means is adapted to select a number of AC coefficients that may be variable for subsequent intra encoded pictures of said trick play signal.  
     
     
         11 . Apparatus as claimed in  claim 10 , wherein the trick play signal generating means is adapted to select for the generation of an intra encoded picture of said trick play signal, for a current subpicture of said intra encoded picture, a number of AC coefficients from the corresponding subpicture of said intra encoded picture of said digital video information signal, said number having a relationship with the difference between the DC coefficient of the current subpicture of said intra encoded picture of said digital information signal from which the present intra encoded picture of the trick play signal will be derived and the DC coefficient of the previous subpicture of said intra encoded picture of said digital video information signal.  
     
     
         12 . Apparatus as claimed in  claim 11 , wherein said number increases for an increasing difference.  
     
     
         13 . Apparatus as claimed in  claim 1 , wherein the trick play signal generating means are adapted to 
 (a) retrieve I pictures from said digital video information signal,    (b) generate P pictures,    (c) merge said I pictures and said P pictures so as to obtain said trick play signal comprising groups of pictures, comprising an I picture followed by a number of n P pictures, the generated P pictures being such that, upon reproduction at said trick play speed, a P picture following an I picture results, upon decoding, in a repeated presentation of a picture obtained from decoding said I picture.    
     
     
         14 . Apparatus as claimed in  claim 7 , wherein said trick play generating means are adapted to data compress an intra encoded picture comprised in said digital video information signal by deleting subpictures of the said picture, starting at the right hand side of the picture, towards the left hand side of the picture.  
     
     
         15 . Apparatus for recording a digital video information signal on a record carrier, the apparatus comprising 
 input means for receiving the digital video information signal,    trick play signal generating means for generating a trick play signal from said digital video information signal, so as to enable a trick play reproduction at a speed m times the nominal reproduction speed, where m is an integer larger than 1,    merging means for merging said digital video information signal and said trick play signal into a composite information signal,    writing means for writing said composite information signal in a track on said record carrier, said trick play signal generating means being adapted to retrieve intra encoded pictures from said digital video information signal, and are adapted to carry out a data compression step on said retrieved intra encoded pictures so as to obtain data compressed intra encoded pictures in said trick play signal.    
     
     
         16 . Apparatus as claimed in  claim 15 , wherein said trick play signal generating means is adapted to data compress intra encoded pictures comprised in said digital video information signal by lowering the resolution of said intra encoded pictures so as to obtain said data compressed intra encoded pictures of said trick play signal.  
     
     
         17 . Apparatus as claimed in  claim 15 , wherein said trick play signal generating means is adapted to data compress intra encoded pictures comprised in said digital video information signal by selecting a restricted number of AC coefficients of said intra encoded pictures so as to obtain said data compressed intra encoded pictures of said trick play signal.  
     
     
         18 . Apparatus as claimed in  claim 17 , wherein the trick play signal generating means is adapted to select a number of AC coefficients that may be variable for subsequent data compressed intra encoded pictures of said trick play signal.  
     
     
         19 . Apparatus as claimed in  claim 18 , wherein the trick play signal generating means is adapted to select for the generation of a data compressed intra encoded picture of said trick play signal, for a current subpicture of said data compressed intra encoded picture, a number of AC coefficients from the corresponding subpicture of said intra encoded picture of said digital video information signal, said number having a relationship with the difference between the DC coefficient of the current subpicture of said intra encoded picture of said digital information signal from which the present data compressed intra encoded picture of the trick play signal will be derived and the DC coefficient of the previous subpicture of said intra encoded picture of said digital video information signal.  
     
     
         20 . Apparatus as claimed in  claim 19 , wherein said number increases for an increasing difference.  
     
     
         21 . Method of recording a digital video information signal on a record carrier, the method comprising the steps of 
 receiving the digital video information signal,    generating a trick play signal from said digital video information signal, so as to enable a trick play reproduction at a speed m times the nominal reproduction speed, where m is an integer larger than 1,    merging said digital video information signal and said trick play signal into a composite information signal,    writing said composite information signal in a track on said record carrier, said trick play signal generating step comprising the substeps of 
 (a) retrieving intra encoded pictures from said digital video information signal,  
 (b) generating inter encoded pictures,  
 (c) merging said intra encoded pictures and said inter encoded pictures, so as to obtain a trick play signal comprising subsequent groups of pictures, comprising an intra encoded picture, followed by a number of n of said generated inter encoded pictures, where n is an integer larger than 0, the generated inter encoded pictures being such that, upon reproduction at said trick play speed, an inter encoded picture following an intra encoded picture results, upon decoding, in a repeated presentation of a picture obtained from decoding said intra encoded picture.  
   
     
     
         22 . Method of recording a digital video information signal on a record carrier, the method comprising the steps of 
 receiving the digital video information signal,    generating means for generating a trick play signal from said digital video information signal, so as to enable a trick play reproduction at a speed m times the nominal reproduction speed, where m is an integer larger than 1,    merging said digital video information signal and said trick play signal into a composite information signal,    writing said composite information signal in a track on said record carrier, said trick play signal generating step comprising the substeps of 
 (a) retrieving intra encoded pictures from said digital video information signal, and  
 (b) carrying out a data compression step on said retrieved intra encoded pictures so as to obtain data compressed intra encoded pictures in said trick play signal.  
   
     
     
         23 . Record carrier having a digital video information signal and a trick play signal recorded on it, said digital video information signal being meant for a reproduction from said record carrier at a nominal play reproduction speed, said trick play signal being meant for a reproduction from said record carrier at a trick play speed m times said nominal reproduction speed, m being an integer larger than 1, said trick play signal comprising subsequent groups of pictures, comprising an intra encoded picture, followed by a number of n of inter encoded pictures, where n is an integer larger than 0, the inter encoded pictures being such that, upon reproduction at said trick play speed, an inter encoded picture following an intra encoded picture results, upon decoding, in a repeated presentation of a picture obtained from decoding said intra encoded picture.