(57) A secondary packetized data stream, such as a commercial, is spliced with a primary
packetized data stream, such as a network television program. The system does not
require decompression of the data in the primary data stream, and is particularly
suitable for use at a cable system headend to allow the insertion of commercials from
local businesses into a nationally broadcast television program. When a start signal
is received, a pre-splicing packet of the primary stream is determined. The pre-splicing
packet is the packet closest to the start time which carries an anchor frame (e.g.,
I or P frame) start code. To prevent a potential discontinuity at the decoder, the
pre-splicing packet is processed to discard the anchor frame data, and to insert a
number of stuffing bytes which is equal to the number of bytes discarded into an adaptation
field of the pre-splicing packet. To further maintain continuity at the decoder, identifying
data of the primary stream such as PID and PSI data, is retrieved and provided to
the secondary stream. A number of null packets are inserted into the output stream
at the transition point between the main program and the commercial to prevent a buffer
overflow at a decoder which receives the output stream.
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