Circuit and method for live switching of digital video programs containing embedded audio data

A method of providing an audio output stream in response to an input stream containing a stream of first program audio samples followed by a stream of second program audio samples, the method comprising:

• (a) receiving the stream of first program audio samples and sequentially storing the first program audio samples in a main audio data buffer;
• (b) reading the first program audio samples from the main audio data buffer and transmitting them as part of the audio output stream;
• (c) detecting a transition in the input stream from the stream of first program input samples to the stream of second program audio samples;
• (d) receiving the stream of second program audio samples and sequentially storing the second program audio samples in a second audio data buffer;
• (e) when the number of first program audio samples in the main audio data buffer reaches a fade-out threshold, transmitting each of the remaining first audio program samples in the audio output stream at progressively lower audio levels;
• and
• (f) when the number of second program audio samples in the second audio data buffer reaches a fade-in threshold, sequentially reading a set of fade-in samples from the second audio buffer and transmitting the fade-in samples as part of the audio output stream at progressively higher audio levels.

A system for transmitting an audio output stream in response to an input stream containing a stream of first program audio samples followed by a stream of second program audio samples, the system comprising:

• (a) an input terminal for receiving said input stream;
• (b) a disruption detector coupled to said input terminal for detecting a transition in said input stream between said stream of first program audio samples and said stream of second program audio samples and for generating a disruption signal corresponding to said transition;
• (c) a transition controller coupled to said disruption detector for generating a main buffer write enable signal and a second buffer write enable signal in response to said disruption signal;
• (d) an audio de-embedder coupled to said input terminal for extracting said first and second program audio samples from input stream and for generating a valid audio sample signal for indicating when valid audio samples are being received;
• (e) a main buffer coupled to said audio de-embedder for receiving and storing said stream of first program audio samples in response to said first buffer write enable signal while valid audio samples are being received;
• (f) a second buffer coupled to said audio de-embedder for receiving and storing said stream of second program audio samples in response to said second buffer write enable signal while valid audio samples are being received;
• (g) a main output controller coupled to said main buffer for reading said first program audio samples from said main buffer and for transmitting a main audio stream corresponding to said first program audio samples, wherein, when the number of said first program audio samples stored in said main buffer is at or below a selected fade-out threshold, said main output controller attenuates the audio level of each remaining first program audio sample in said main audio stream;
• (h) a second output controller coupled to said second buffer for reading said second program audio samples from said second buffer and for transmitting a second audio stream corresponding to said second program audio samples, wherein, said second output controller is configured to attenuate the audio level of a selected number of fade-in second program audio samples in said second output stream, wherein said second output controller is configured to begin reading said second program audio samples after the number of said first program audio samples stored in said main buffer is at or below the selected fade-out threshold;
• (i) a summer coupled to main output controller and to said second output controller for generating said audio output stream corresponding to said main output stream and said second output stream,
• wherein said transition controller configures said main buffer write enable signal and said second buffer write enable signal such that, prior to the detection of said transition, said main buffer is enabled and said second buffer is disabled and, after said transition, said main buffer is disabled and said second buffer is enabled.