Device and method for decoding digital TV broadcast
View Patent ↗For use as or in connection with a set-top box, a digital TV broadcast signal is decoded by processing its audio stream into and read from a FIFO buffer. According to certain embodiments, fullness of the FIFO buffer is compared to a reference fullness, which can be updated based on changes to the bit rate of the audio stream. In response to the FIFO buffer fullness, the set top box regulates the rate at which the audio stream is decoded. The disclosed decoding methods do not need to rely on the accuracy or presence of a system time encoded into the broadcast signal.
1. For use in a set-top box (STB) that receives a digital TV broadcast having an audio stream with a coded bit rate, and that processes a representation of the audio stream through a first-in-first-out (FIFO) buffer, a method performed in the STB, comprising:
comparing an indication of FIFO fullness to a reference FIFO fullness, the reference FIFO fullness being based on the coded bit rate, and in response thereto, adjusting a local clock frequency to regulate a rate at which a representation of the audio stream of the original TV broadcast is processed from the FIFO; and
identifying changes in the coded bit rate, and in response thereto, updating the reference FIFO fullness.
2. The method of claim 1 , wherein the indication of FIFO fullness is a measurement based on the number of bytes written into the FIFO buffer, the number of bytes read from the FIFO buffer, and the FIFO buffer size.
3. The method of claim 1 , wherein the indication of FIFO fullness is an estimation based on an initial FIFO fullness, a determined bit rate into the FIFO buffer, and a determined bit rate out of the FIFO buffer.
4. The method of claim 1 , wherein the bit rate is an average bit rate.
5. The method of claim 1 , further including initializing the reference FIFO fullness.
6. The method of claim 1 , wherein the method is performed upon an indication that a system time encoded into the broadcast does not match the local clock time at the set-top box.
7. The method of claim 1 , further comprising decoding the audio stream using the local clock of the set-top box.
8. The method of claim 1 , wherein regulating the rate at which a representation of the audio stream is processed from the FIFO comprises correcting a local clock that regulates the rate.
9. A set-top box that receives a digital TV broadcast having an audio signal with a coded bit rate and that processes a representation of the audio signal through a first-in-first-out (FIFO) buffer, the set-top box comprising:
a data-decoding circuit to decode and extract the bit rate from the digital TV broadcast's audio signal;
a circuit for providing an indication of FIFO fullness based on an indication of bytes written to the FIFO buffer, an indication of bytes read from the FIFO buffer, and FIFO buffer size; and
a rate-adjustment circuit to compare the indication of FIFO fullness to a reference FIFO fullness, the reference FIFO fullness being based on the extracted bit rate, and, in response thereto, adjusting a local clock frequency to regulate a rate at which a representation of the audio signal is processed from the FIFO, the rate-adjustment circuit also serving to update the reference FIFO fullness in response to changes in the extracted bit rate.
10. A device for decoding a received digital TV broadcast signal, the device comprising:
a de-multiplexer configured to extract an audio stream from the received digital TV broadcast signal;
an audio decoder configured for decoding the audio stream using a local clock;
a first-in-first-out (FIFO) buffer to which the de-multiplexer writes audio stream data and from which the audio decoder reads audio stream data;
a correction circuit configured to develop a correction for the local clock based on a comparison of a fullness reference of the FIFO buffer developed from bit rate information in the extracted audio stream and a FIFO fullness; and
a circuit to update the fullness reference in response to changes in the bit rate information.
11. The device of claim 10 , wherein FIFO fullness is a measurement based on the number of bytes written into the FIFO buffer, the number of bytes read from the FIFO buffer, and the FIFO buffer size.
12. The device of claim 10 , wherein FIFO fullness is an estimation based on an initial FIFO fullness, a determined bit rate into the FIFO buffer, and a determined bit rate out of the FIFO buffer.