JP4296652B2 - Digital signal recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital signal recording apparatus that generates a bit stream such as an MPEG (Motion Picture Expert Group) transport stream and records the bit stream on a recording medium.
[0002]
[Prior art]
A D-VHS (registered trademark) video tape recorder (VTR) is known as a device for recording digitized image signals and audio signals. This type of VTR has a function of storing an MPEG transport stream transmitted from a television station in a predetermined sync block and recording and reproducing it as it is.
[0003]
[Problems to be solved by the invention]
When recording an analog image signal and an audio signal on a VTR having such a function, the analog image signal and the audio signal are digitized and subjected to information compression processing conforming to the MPEG standard, and transmitted from a television station. A method of recording by converting into a bit stream similar to the transport stream is conceivable. In that case, if the encoding rate in the encoder that generates the bitstream is arbitrarily set, the packet interval may not be constant.
[0004]
For example, when the reference clock frequency is 27 MHz and one packet is 1504 bits (188 bytes × 8 bits) and the bit rate is set to 1,505,504 bps (bits / second), the number of packets per second is 1001 packets. However, if the packet interval is 26974 clocks, the bit rate will be less than 1,505,504 bps, and if it is 26973 clocks, it may be greater than 1,505,504 bps. Therefore, in order to make the bit rate always constant 1,505,504 bps, the interval of 27 packets out of 1001 packets must be 26974 clocks, the interval of 974 packets must be 26973 clocks, and the packet interval is constant. Can not do it.
[0005]
The packet interval at the time of encoding in the encoder is a predetermined constant interval TPC, but when transferring from the encoder to the VTR as the recording device, the transfer efficiency is higher when the packet interval is shortened. Therefore, it is advantageous to perform recording by shortening the packet interval and transferring it to the original interval TPC on the VTR side. However, when the packet interval at the time of encoding is not constant, there arises a problem that the process of returning the packet interval on the VTR side becomes complicated.
[0006]
The present invention has been made paying attention to this point, and includes an encoder that generates a packetized bit stream such as an MPEG transport stream, and a recording unit that records the bit stream on a recording medium. It is an object of the present invention to provide a digital signal recording apparatus that can change the encoding rate of the recording unit as required, and can simplify the packet interval reproduction processing of the recording unit.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 is a function for generating a packetized bitstream by performing predetermined information compression processing on one or more input signals and time-division multiplexing. And an encoder capable of changing the encoding rate, and a bit stream recording unit that performs a predetermined process on the output signal of the encoder and records it on a recording medium. The encoder encodes at a predetermined packet interval. However, the packet interval is transferred to the bit stream recording unit without maintaining the packet interval, and the bit stream recording unit returns the packet interval of the transferred bit stream to the predetermined packet interval for recording. When the encoding rate is set as a bit rate, the predetermined packet interval is set as a reference clock. And k is a period that is k times (k is a positive integer), and k is selected and set from a divisor of (number of reference clocks per second fCLK × number of bits of one packet nBP). To do.
[0008]
According to a second aspect of the present invention, in the digital signal recording apparatus according to the first aspect, the integer k corresponding to the predetermined packet interval is set to a reference clock number fCLK / 10 or less per second. To do.
[0009]
The invention according to claim 3 has a function of generating a packetized bit stream by performing predetermined information compression processing on one or more input signals and time-division multiplexing the encoding signal. And a bit stream recording unit that performs a predetermined process on the output signal of the encoder and records it on a recording medium, and the encoder performs encoding at a predetermined packet interval. The bit stream recording unit is configured to perform recording by returning the packet interval of the transferred bit stream to the predetermined packet interval without holding the interval. The encoding rate is the number of packets nPFLD per predetermined period equal to m times the reference clock period (m is a positive integer). When the constant is characterized by selecting and setting the number of packets nPFLD from the divisor of the integers m.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of a digital signal recording apparatus according to an embodiment of the present invention. This apparatus is based on the MPEG2 standard for three systems of input signals SIN1, SIN2, and SIN3 consisting of image and audio signals. MPEG-TS encoder 1 that generates an MPEG transport stream and outputs a transfer packet stream STR with a changed packet interval by performing an information compression encoding process and a time-division multiplexing process compliant with the above, and a transfer packet stream STR The original MPEG transport stream is returned, the bit stream recording unit 2 that performs predetermined processing and records it on the recording medium, and the clock generation that generates the 27 MHz reference clock signal SCLK used in the encoder 1 and the bit stream recording unit 2 Part 3.
[0011]
The encoder 1 is configured so that an encoding rate (amount of data encoded per unit time) ER can be changed according to a control signal from the outside. When the encoding rate ER is designated, the encoder 1 generates a packet with a constant packet interval TPC corresponding to the rate and stores it in the memory, and generates a transfer packet stream STR with the original packet interval TPC shortened. Then, the data is transferred to the bit stream recording unit 2.
[0012]
As shown in FIG. 2, the bit stream recording unit 2 includes a packet interval restoration circuit 11 that restores the transfer packet stream STR to an MPEG transport stream STS having an original packet interval TPC, and a D- DVHS format signal processing circuit 12 that performs recording signal processing compliant with the VHS standard, recording amplifier 13 that amplifies the output signal of DVHS format signal processing circuit 12, and magnetic head that records the output signal of recording amplifier 13 on magnetic tape 50 14. The packet interval of the transfer packet stream STR transferred from the encoder 1 is returned to the original packet interval TPC by the packet interval restoration circuit 11 and subjected to recording signal processing of the D-VHS standard to be applied to the magnetic tape 50 as a recording medium. To be recorded.
[0013]
As shown in FIG. 3, the packet interval restoration circuit 11 includes a memory 21 that temporarily stores a transfer packet stream STR and a read control unit 22 that performs read control of the memory 21. The read control unit 22 performs control so that one packet is read at every fixed reference clock number set according to the encoding rate ER so that the packet interval becomes the original packet interval TPC.
[0014]
Next, in the present embodiment, when the encoding rate ER of the encoder 1 is controlled, when the encoding rate ER is set at the bit rate BR, (the number of reference clocks fCLK = 27,000,000 per second) × 1504 bits A packet interval TPCCLK is set from the divisors, and a bit rate BR corresponding to the packet interval TPCCLK is set. Here, the packet interval TPCCLK is the number of reference clocks generated during the period of the packet interval TPC (sec), that is, the packet interval indicated by the number of reference clocks (corresponding to the integer k described in claim 1), and the reference clock cycle. Is TCLK (= 1 / fCLK), it is defined as follows.
TPCCLK = TPC / TCLK = TPC × fCLK
1504 bits are the number of bits of one packet (188 bytes × 8 bits) constituting the MPEG2 transport stream.
[0015]
The setting condition of the packet interval TPCCLK is derived as follows. Assuming that the number of bits per packet is 1504 bits and nBP and the number of packets per second is nPSEC, the bit rate BR is
BR = nBP × nPSEC (1)
Further, the number of packets nPSEC per second can be expressed by the following equation (2) using a reference clock number fCLK per second and a one-packet interval TPCCLK (clock).
nPSEC = fCLK / TPCCLK (2)
[0016]
Therefore, when the formula (2) is applied to the formula (1), the following formula (3) is obtained.
BR = nPB × fCLK / TPCCLK (3)
Equation (3) shows that the bit rate BR can be made an integer by setting the packet interval TPCCLK to a divisor of fCLK × nPB (= 27,000,000 × 1504).
[0017]
If the packet interval TPCCLK is set so as to satisfy the above condition, the bit rate BR can be set to an integer, and a constant bit rate BR and a constant packet interval TPCCLK can always be realized. As a result, the packet interval restoration circuit 11 only needs to perform a process of reading out one packet for every fixed reference clock number, so that the packet interval can be restored with a simple circuit. Further, when the encoding rate ER is changed, it is only necessary to change the read cycle from the memory 21, which is also advantageous in this respect.
[0018]
As a specific example, when the packet interval TPCCLK is 1,350,000 which is a divisor of (27,000,000 × 1504), the number of packets per second nPSEC is 27,000,000 / 13,000,000 = 20. Thus, the bit rate BR becomes constant at nPSEC × 1504 = 30,080 (bps).
[0019]
On the other hand, for example, if the packet interval is a value that is not a divisor of (27,000,000 × 1504), the bit rate BR varies depending on how to take a sampling period of 1 second. FIG. 4 is a time chart for explaining this point. In FIG. 4, t0, t1, t2, .about.ti, ti + 1, ti + 2 indicate times at intervals of one second. FIG. 5A shows the case where the packet interval TPCCLK = 1,350,000, which is constant at 20 packets per second and the bit rate BR = 30080, whereas the packet interval TPCCLK is slightly less than 1,350,000. The number of packets nPC per second is slightly increased from 20 (20.x), and the bit rate BR1 from time t0 to ti + 1 and the bit rate BR2 after time ti + 1 are It becomes different (BR1> BR2 in the illustrated example), and the condition that the bit rate is always constant (however the sampling period of 1 second is set) is not satisfied.
[0020]
The MPEG standard stipulates that an effective PCR (Program Clock Reference) should be transmitted at intervals of 0.1 seconds or less, so the number of packets per second nPSEC is 10 or more. In other words, it is necessary to set the packet interval TPCCLK ≦ fCLK / 10.
[0021]
In this embodiment, when the encoding rate ER of the encoder 1 is controlled, when the encoding rate ER is set by the number of packets nPCFLD per field of the image signal, a divisor of the number of reference clocks corresponding to one field period TFLD. Select from and set.
[0022]
Since one field period TFLD is 450,000 times or 450,450 times the reference clock period TCLK (= 1 / 277,000,000), 450,000 or 450,450 (= 1 indicated by the number of reference clocks). By selecting the number of packets nPFLD from a divisor of the field period TFLDCLK), TFLDCLK / nPFLD (= TPCCLK) becomes an integer, and the number of packets nPFLD in one field period is always constant at a constant packet interval. Can do. TFLDCLK corresponds to the integer m described in claim 3.
[0023]
The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, an encoder that generates an MPEG transport stream and outputs it after changing the packet interval has been described. However, the information compression process and the time-division multiplexing process are performed to perform the same as the MPEG transport stream. If the packetized bit stream is generated, the present invention can be applied.
[0024]
The present invention is applicable not only when the one-field period TFLD is 450,000 times or 450450 times the reference clock period TCLK but also when the predetermined period for defining the encoding rate is an integral multiple of the reference clock period TCLK. is there.
[0025]
【The invention's effect】
As described above in detail, according to the first aspect of the present invention, predetermined information compression processing is performed on one or more input signals, and a packetized bit stream is generated by time division multiplexing. And an encoder capable of changing the encoding rate, and a bit stream recording unit that performs a predetermined process on the output signal of the encoder and records it on a recording medium, wherein the encoder has a predetermined packet interval The bit stream recording unit transfers the packet interval of the transferred bit stream back to the predetermined packet interval for recording without holding the packet interval. In the digital signal recording apparatus configured to perform, when the encoding rate is set as a bit rate, When the predetermined packet interval is a period of k times the reference clock period (k is a positive integer), k is selected from a divisor of (the number of reference clocks fCLK × the number of bits of one packet nPKT per second). Thus, the packet interval is always constant, the bit rate can be a constant integer value, and the packet interval reproduction process of the bit stream recording unit can be simplified.
[0026]
According to a third aspect of the present invention, when the encoding rate is set by the number of packets per predetermined period equal to m times a reference clock period (m is a positive integer), a divisor of the integer m Therefore, the packet interval can be made constant and the number of packets within a predetermined period can be made constant, and the packet interval reproduction process of the bit stream recording unit can be simplified.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a digital signal recording apparatus according to an embodiment of the present invention.
2 is a block diagram showing a configuration of a bit stream recording unit in FIG. 1; FIG.
FIG. 3 is a block diagram showing a configuration of a packet interval restoration circuit.
FIG. 4 is a time chart for explaining a change in bit rate when the setting of a packet interval is inappropriate.
[Explanation of symbols]
1 MPEG-TS encoder 2 Bit stream recording unit 3 Reference clock generation unit 11 Packet interval restoration circuit

Claims (3)

An encoder capable of performing a predetermined information compression process on one or more input signals and generating a packetized bitstream by time-division multiplexing, and capable of changing an encoding rate;
A bitstream recording unit that performs a predetermined process on the output signal of the encoder and records it on a recording medium;
The encoder performs encoding at a predetermined packet interval, but transfers the packet interval of the transferred bit stream to the bit stream recording unit without holding the packet interval. Is configured to record back to the packet interval of
When the encoding rate is set as a bit rate, the predetermined packet interval is set to a period of k times the reference clock period (k is a positive integer), and k is (the number of reference clocks fCLK × 1 packet per second). A digital signal recording apparatus characterized in that it is selected and set from divisors of bit number nBP). 2. The digital signal recording apparatus according to claim 1, wherein the integer k corresponding to the predetermined packet interval is set to a reference clock number fCLK / 10 or less per second. An encoder capable of performing a predetermined information compression process on one or more input signals and generating a packetized bitstream by time-division multiplexing, and capable of changing an encoding rate;
A bitstream recording unit that performs a predetermined process on the output signal of the encoder and records it on a recording medium;
The encoder performs encoding at a predetermined packet interval, but transfers the packet interval of the transferred bit stream to the bit stream recording unit without holding the packet interval. Is configured to record back to the packet interval of
When the encoding rate is set by the number of packets nPFLD per predetermined period equal to m times the reference clock period (m is a positive integer), the number of packets nPFLD is selected from the divisors of the integer m. A digital signal recording apparatus characterized by setting.

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