Data compression unit control for alignment of output signal

Abstract

To enable a single programme in a multiple programme MPEG transport stream (MPTS) to be replaced seamlessly by a locally generated programme, the local coder receives the MPTS as a reference signal and outputs transport packets in alignment with the packets of the programme to be replaced. Timing and other packet parameters are also copied.

1 . A method of controlling a compression unit which outputs a compressed bitstream in packets, the method comprising. 
 supplying to a reference input of the compression unit, a transport stream input with a sequence of transport packets;    supplying to a second input of the compression unit an input to be compression coded; and    nominating a set of the transport packets as reference packets and arranging for the compression unit to compression code the input and output the compression coded bit-stream in packets that are in alignment with the reference packets.    
     
     
         2 . A method according to  claim 1 , wherein the transport stream comprises a multiprogramme transport stream and wherein the nominated set of transport packets comprises those packets associated with a selected programme.  
     
     
         3 . A method according to  claim 2 , wherein the nominated set of transport packets comprises sub-sets of packets, those sub-sets being associated with respective elementary streams of the selected programme.  
     
     
         4 . A method according to  claim 1 , wherein each said compression unit is arranged to output packets having at least one parameter determined by the reference packet with which it is in alignment.  
     
     
         5 . A method according to  claim 4 , wherein said parameter is a clock reference.  
     
     
         6 . A method according to  claim 4 , wherein said parameter is the location of a frame start.  
     
     
         7 . A method according to  claim 4 , wherein said parameter is a time stamp.  
     
     
         8 . A method according to  claim 4 , wherein said parameter is a delay value.  
     
     
         9 . A method of replacing a programme within a multi-programme transport stream by the output of a programme compression unit, the method comprising: 
 supplying to the compression unit the multi-programme transport stream and a programme input;    nominating as reference packets those packets which are associated with the programme to be replaced;    arranging for the compression unit to compression code the programme input and output the encoded programme stream in packets in alignment with the reference packets; and    re-multiplexing the output of a the programme compression unit with the remaining packets of the multi-programme transport stream.    
     
     
         10 . A method according to  claim 9 , wherein the programme compression unit comprises a compression encoder receiving an uncompressed programme input.  
     
     
         11 . A method according to  claim 9 , wherein the programme compression unit comprises a compression transcoder receiving a compressed programme stream input.  
     
     
         12 . A method according to  claim 9 , wherein the compression unit is arranged to output packets having at least one parameter determined by the reference packet with which it is in alignment.  
     
     
         13 . A method according to  claim 12 , wherein said parameter is a clock reference.  
     
     
         14 . A method according to  claim 12 , wherein said parameter is the location of a frame start.  
     
     
         15 . A method according to  claim 12 , wherein said parameter is a time stamp.  
     
     
         16 . A method according to  claim 12 , wherein said parameter is a delay value.  
     
     
         17 . Apparatus for replacing a programme within a multi-programme transport stream by the output of a programme compression unit, the apparatus comprising: 
 a compression unit having a reference input and a programme input;    means for supplying the multi-programme transport stream to said reference input and a programme input to said programme input, and nominating as reference packets those packets which are associated with the programme to be replaced;    the compression unit being arranged to compression code the programme input and output the encoded programme stream in packets in alignment with the reference packets; and    a re-multiplexer for re-multiplexing the output of the programme compression unit with the multi-programme transport stream.    
     
     
         18 . Apparatus according to  claim 17 , wherein the programme compression unit comprises a compression encoder receiving an uncompressed programme input.  
     
     
         19 . Apparatus according to  claim 17 , wherein the programme compression unit comprises a compression transcoder receiving a compressed programme stream input.  
     
     
         20 . Apparatus according to  claim 17 , wherein the compression unit is arranged to output packets having at least one parameter determined by the reference packet with which it is in alignment.  
     
     
         21 . Apparatus according to  claim 20 , wherein said parameter is a clock reference.  
     
     
         22 . Apparatus according to  claim 20 , wherein said parameter is the location of a frame start.  
     
     
         23 . Apparatus according to  claim 20 , wherein said parameter is a time stamp.  
     
     
         24 . Apparatus according to  claim 20 , wherein said parameter is a delay value.  
     
     
         25 . A method of controlling a plurality of compression units which each output a compressed bit-stream, the method comprising: 
 supplying to a reference input of each of the compression units, a transport stream input with a sequence of transport packets;    supplying to a second input of each compression unit an input to be compression coded; and    nominating a different set of the transport packets as reference packets for each of the respective compression units and arranging for each compression unit to compression code the input for that compression unit and output the encoded programme stream in packets in alignment with the reference packets nominated for that compression unit.    
     
     
         26 . A method according to  claim 25 , wherein some or all of the compression units comprise a compression encoder receiving an uncompressed input.  
     
     
         27 . A method according to  claim 25 , wherein some or all of the compression units comprise a compression transcoder receiving a compressed input stream.  
     
     
         28 . A method according to  claim 25 , wherein the relative occurrences of the different sets of packets in the transport stream input are varied to control the relative bit rates of the respective compression unit outputs.  
     
     
         29 . A method according to  claim 28 , wherein the activity of each compression unit is monitored to inform said control of relative bit rates.  
     
     
         30 . A method according to  claim 25 , wherein the outputs of the respective compression units are combined to form a multi-programme transport stream in which the overall bit rate and the instantaneous allocation of that bit rate amongst the programme transport streams is defined by said transport stream reference.  
     
     
         31 . A method according to  claim 30 , wherein the outputs of the respective compression units are combined by OR'ing.  
     
     
         32 - 34 . (canceled)