Data stream processor

#The present invention relates to a data stream processor that performs processing such as encoding or decoding for data, particularly data including video and/or audio information.

#The international standard MPEG2 (Moving Picture Experts Group 2) is one method for compressing audiovisual information. MPEG2 is a method that individually compresses video and audio and synchronizes and multiplexes the compressed video, audio, data, etc. MPEG2 is suitable for storage media, networks, etc. There are two types of MPEG2: MPEG2-PS (Program Stream) for multiplexing and demultiplexing a single program and MPEG2-TS (Transport Stream) for a plurality of programs. MPEG2-TS can handle a plurality of program data as a sequence of data (hereafter referred to as a “data stream”) and is mainly used for television broadcasting services.

#Data to be compressed by MPEG2-TS includes a Decoding Time Stamp (DTS) and Presentation Time Stamp (PTS) for times of decoding and presenting each frame of video and audio information. Further, compressed data include two types of time information: System Clock Reference (SCR) and Program Clock Reference (PCR). These types of information are used for a decoder to decode compressed data (hereafter simply referred to as “decoder”). The decoder uses SCR and PCR to correct a System Time Clock (STC) value to an intended value for a coder to compress data (hereafter simply referred to as “coder”).

#FIG. 1 shows a configuration of a data stream processor according to the present invention;

#FIG. 2 shows a configuration of a data stream decoder according to the present invention;

#FIG. 3 shows another configuration of a data stream coder according to the present invention;

#FIG. 1 shows a configuration of a data stream processor 1 according to a preferred embodiment of the present invention. The term data stream processor is used herein as a generic name for a data coder, a data decoder, and a data coder/decoder. Data stream processor 1 has a reference frequency control section 11 and a data stream control section 12. Reference frequency control section 11 provides a reference frequency that defines timings for data transmission etc. in the apparatus based on time information supplied from the outside of data stream processor 1. Data stream control section 12 temporarily stores an externally supplied data stream and outputs the data stream based on the reference frequency determined by a signal generated from reference frequency control section 11. Reference frequency control section 11 includes an oscillator 13, a reference time counter 16, an oscillator control section 17, and a reference time information acquisition section 15.

#Reference time counter 16 is incremented synchronously with the reference frequency (27 MHz in this embodiment) defined by a clock signal generated from oscillator 13. Oscillator control section 17 controls oscillator 13 using a difference between a value of reference time counter 16 and the external time information obtained by reference time information acquisition section 15. The NTP (Network Time Protocol) is an example of the time information obtained by reference time information acquisition section 15.

#FIG. 10 is a diagram of an NTP format. The NTP time information is a 232 Hz (approximately 4 GHz) counter value comprised of the number of seconds (32 bits representing time since Jan. 1, 1900 and the fractional portion (32 bits) of a second. Oscillator control section 17 holds the NTP external time information and a value of reference time counter 16 when the NTP was obtained. Thereafter, oscillator control section 17 compares next obtained NTP time information and a value of reference time counter 16 at that time with the previously stored time information and the value of reference time counter 16 to compute each increase. Further, oscillator control section 17 compares an increase in the NTP time information with an increase in the value of reference time counter 16 and controls oscillator 13 according to the difference.