Switching between bit-rate reduced signals
AssigneeBritish Broadcasting Corporation
InventorNicholas Dominic Wells
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Abstract
A switch arrangement is provided for MPEG or other bit-rate signals. An output switch (66) is arranged to switch between bitstream A; an interim bitstream developed about the switch point; and bitstream B. The interim bitstream is provided by a re-coder (64) the input to which is switched at (58) between a decoder (52) for bitstream A and a decoder (56) for bitstream B.
Claims45
A method of switching a bit-rate reduced signal, comprising the steps of:
- developing a re-coded signal in synchronism with the bit-rate reduced signal by passing the bit-rate reduced signal through a decoder and re-coder pair;
- switching between the bit-rate reduced signal and the synchronized re-coded signal at an appropriate signal point selected to produce minimal disturbance in a downstream decoder;
- and subsequently switching the input of the re-coder to an alternative signal source.
An apparatus for switching a bit-rate reduced signal at an output terminal, comprising:
- an input terminal for receiving a bit-rate reduced signal;
- an output switch, a direct appropriately delayed path for passing the bit-rate reduced signal to the output switch without decoding;
- a decoder for receiving the bit-rate reduced signal;
- a coder for receiving the decoded, bit rate reduced signal from the decoder and for supplying a re-coded signal to the output switch, wherein the coder receives buffer occupancy information from the decoder and;
- the output switch is adapted to switch at the output terminal between the bit-rate reduced signal and the re-coded signal;
- and
- re-coder switch means for receiving an alternative signal and applying it to the coder in substitution for said decoded signal.
In an arrangement of first and second signals where each signal is capable of representation in coded and decoded forms, the coded form comprising a sequence of frames including both reference frames and frames defined with respect to reference frames, the method of switching between the first signal in coded form and the second signal in coded form, comprising the steps of:
- receiving the first signal in coded form;
- decoding and recoding the first signal to provide a recoded first signal in frame synchronization with the coded first signal as received;
- switching in the coded domain between the coded first signal as received and the frame synchronized recoded first signal;
- and
- switching in the uncoded domain between the decoded first signal and the second signal.
A system comprising:
- a downstream decoder having a data buffer;
- at least one upstream coder utilizing a data buffer to derive a bit-rate reduced signal for decoding in the downstream decoder where the variation of occupancy of the downstream decoder data buffer is determined by the variation of occupancy of the upstream coder;
- and
- at least one re-coder in a path between the upstream coder and the downstream decoder, wherein the data occupancy of said re-coder is constrained to follow that of the upstream coder thereby enabling a switch to be made from said bit-rate reduced signal, without discontinuity in the downstream decoder data buffer.
Dependencies are inferred from the claim text.