Abstract: A digital radio broadcast system provides various interactive features, including skip forward and skip backward. In one embodiment, data is transmitted at a faster than real time rate and accumulated in a buffer at a receiver. The user can play a current track or skip to subsequent or earlier tracks. In another embodiment, two or more programming service streams (i.e., user channels) are communicated such that a user can move directly from a current track to the beginning of a track of another stream. In another embodiment, tiers of service levels are provided so that paying subscribers can bypass some or all of the commercial messages, while non-paying subscribers can not bypass the commercials. Replacement programming may be transmitted in a portion of the bandwidth of the free service. At a receiver, control data may be used with multimedia data to provide a multimedia clip which identifies features of a track, such as artist, song title or lyrics.

Abstract: A method and apparatus are provided for communicating HBI user information in digital television data streams via a generic syntax. The syntax allows the digital transport of virtually any type of user data that may be carried in the HBI or overscan portion of an analog television signal. A pixel generator is used to insert HBI data into a digital video signal using information provided in the user portion of the digital data stream. The syntax provides the pixel generator with the start time of the first symbol, the number of pixels per symbol, the high and low levels to insert, the fraction of the symbol time that is transition time, the number of symbols to insert and the first frame line number on which to insert the data.

Abstract: A digital waveform generator complies with different vertical blanking interval (VBI) standards, and is inserted into VBI portions of a digital component video signal. A buffer receives symbols carrying VBI data for a particular VBI service according to a user data syntax, which identifies a television line into which the VBI data is to be inserted. A symbol processor is responsive to information provided by the syntax. This information indicates the number of pixels represented per symbol, a symbol transition time, and the number of symbols carrying data to be inserted into the VBI portion. The symbol processor provides the VBI data in a format according to the particular VBI service. A timing circuit is responsive to a start time provided by the syntax for inserting the VBI data. A level control circuit adjusts the level of the VBI data prior to insertion into the VBI portion in response amplitude values provided by the syntax.

Abstract: Audio data is processed from a packetized data stream carrying digital television information in a succession of fixed length transport packets. Some of the packets contain a presentation time stamp (PTS) indicative of a time for commencing the output of associated audio data. After the audio data stream has been acquired, the detected audio packets are monitored to locate subsequent PTS's for adjusting the timing at which audio data is output, thereby providing proper lip synchronization with associated video. Errors in the audio data are processed in a manner which attempts to maintain synchronization of the audio data stream while masking the errors. In the event that the synchronization condition cannot be maintained, for example in the presence of errors over more than one audio frame, the audio data stream is reacquired while the audio output is concealed.

Abstract: Variable rate data is reformatted for communication to an external device at a fixed rate. Fixed length packets of the variable rate data are recovered from a multiplex of data packets. A packet start byte is added to the beginning of each of the recovered packets. Fill bits are added to the recovered packets as necessary to maintain the desired fixed output rate if the output rate is greater than an information rate of the variable rate data. The recovered packets with the added packet start byte and fill bits are provided as output to the external device at the fixed rate. The recovered packets with the added packet start byte and fill bits are advantageously encoded using alternate mark inversion (AMI) and binary eight zero substitution (B8ZS). The packet start byte and B8ZS substitution can comprise unique AMI violation sequences.

Abstract: The apparent accuracy of a clock circuit used to recover timing and transmitted information signals in a data receiver is improved. A timing relationship inherent in a received signal is detected prior to the acquisition of a timing component embedded in a desired information portion of the received signal. The timing relationship has an accuracy that is greater than the accuracy of the clock circuit. The clock circuit is controlled in response to the timing relationship to operate with an improved range of accuracy. Thereafter, the embedded timing component is acquired and used to control the clock circuit. In an illustrated embodiment, the timing relationship is derived from a symbol rate of the received signal. In an alternate embodiment, the timing relationship is obtained from a separate transmitted reference signal, such as a transmitted television signal.

Abstract: Television distribution apparatus includes a satellite television receiving station for receiving and demodulating a television signal transmitted as a frequency modulated signal from a satellite. Timing information is recovered from the demodulated television signal. The amplitude of data portions of the demodulated television signal is adjusted in response to the timing information to a level suitable for transmission using amplitude modulation. The original amplitude of television information portions of the signal is maintained. The demodulated television signal with the adjusted data portions is amplitude modulated for distribution to a plurality of subscriber locations.