Transmission rate adjustment device and method

Abstract

A transmission rate adjustment device for supplying MPEG-TS at a desired transmission rate includes: a buffer; a buffer write unit for both sequentially writing to the buffer transport packets of the transport stream that have been read from an MPEG2-TS file and detecting time stamps in the transport stream; and a buffer read unit for transmitting to the MPEG decoder transport packets that have been sequentially read from the buffer at a transmission rate determined by a clock obtained by frequency-dividing a system clock of the MPEG decoder by a frequency division rate designated by a frequency division rate signal. The buffer read unit not only inserts NULL packets between transport packets, but also rewrites time stamps when adjustment cannot be realized by merely inserting the NULL packets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows the typical configuration of an MPEG-TS transport packet;

FIG. 2 is a block diagram showing the configuration of the transport stream reproduction device described in JP-A-2001-339688;

FIG. 3 is a block diagram showing the schematic configuration of the transmission rate adjustment device that is an embodiment of the present invention;

FIG. 4 is a view for explaining the transport packets and appended information that are stored in the buffer shown in FIG. 3;

FIG. 5 is a view for explaining the adjustment of transmission rate in the transmission rate adjustment device shown in FIG. 3;

FIG. 6 is a view for explaining PCR compensation in the transmission rate adjustment device shown in FIG. 3;

FIG. 7 is a block diagram showing the schematic configuration of an MPEG decoder;

FIG. 8 shows the relation between frequency division rate and transmission rate;

FIG. 9 is a schematic view showing an example of the transport stream in which NULL packets are uniformly inserted;

FIG. 10 is a view for explaining the example of insertion of NULL packets in the transmission rate adjustment device shown in FIG. 3;

FIG. 11 is a view for explaining another example of insertion of NULL packets in the transmission rate adjustment device shown in FIG. 3;

FIG. 12 is a view for explaining the changes in the data values that are stored in a transport buffer in the case of uniform insertion of NULL packets; and

FIG. 13 shows the transition in the data values that are stored in a transport buffer in the case of uniform insertion of NULL packets.

Claims

1. A transmission rate adjustment device for adjusting a transmission rate of an input transport stream, the transmission rate adjustment device taking as input a transport stream that comprises a plurality of transport packets having a fixed packet length in which encoded data are stored, and in which time stamps of a prescribed frequency that is a standard time interval during said encoding are inscribed at fixed time intervals, said transmission rate adjustment device comprising: a buffer;a buffer write unit that both successively writes transport packets of said input transport stream to said buffer and detects time stamps in said input transport stream; anda buffer read unit that takes as input both a frequency division rate signal that designates a frequency division rate and a system clock of a decoder for decoding said encoded data, and that transmits to said decoder transport packets that have been sequentially read from said buffer at a transmission rate determined by a clock obtained by frequency-dividing an input system clock by the frequency division rate designated by the input frequency division rate signal;wherein:said buffer write unit, upon detecting said time stamps, stores in said buffer; a difference between a first time stamp that has been detected this time and a second time stamp that was previously detected, a number of transport packets that exist in an interval between the first and second time stamps, and a value of said second time stamp as appended information of the transport packet to which said second time stamp is inscribed; andsaid buffer read unit, upon reading from said buffer a transport packet to which said second time stamp has been inscribed, based on said appended information that has been attached to the transport packet, inserts NULL packets between transport packets that have been read from said buffer to achieve adjustment such that said transport packets are transmitted at said transmission rate, and when adjustment cannot be achieved by a mere insertion of NULL packets, when reading from said buffer the transport packet in which said first time stamp has been inscribed, rewrites the time stamp of the transport packet.

2. A transmission rate adjustment device according to claim 1, wherein said buffer read unit uniformly inserts said NULL packets between transport packets that have been read from said buffer.

3. A transmission rate adjustment device according to claim 2, wherein said buffer read unit, based on the difference between said first and second time stamps and a transmission rate determined by a clock obtained by frequency-dividing said input system clock: calculates a number of transport packets between said first and second time stamps after transmission rate adjustment, and from results of this calculation, calculates a number of NULL packets that should be inserted; and when a calculation result of dividing the calculated number of NULL packets by said calculated number of transport packets contains a quotient and a remainder, inserts a number of NULL packets that corresponds to said quotient for each of transport packets that have been read from said buffer; and further, uniformly inserts a number of NULL packets that corresponds to said remainder in a state in which said NULL packets are inserted.

4. A transmission rate adjustment device according to claim 2, wherein said buffer read unit, based on the difference between said first and second time stamps and a transmission rate determined by a clock obtained by frequency-dividing said input system clock: calculates a number of transport packets between said first and second time stamps after transmission rate adjustment, and from results of this calculation, calculates a number of NULL packets that should be inserted; when a standard average insertion spacing obtained by dividing the calculated number of NULL packets that should be inserted by said number of transport packets that exist between said first and second time stamps is a decimal, takes a value of a whole number portion as a first insertion spacing and a value obtained by adding 1 to this value as a second insertion spacing; and, based on a size relation of an average insertion spacing of NULL packets after NULL packets have been inserted and said standard average insertion spacing, selects between said first and second insertion spacing and inserts one NULL packet for each of transport packets of a number of the value of the selected insertion spacing.

5. A transmission rate adjustment device according to claim 2, wherein said difference between a number of NULL packets that are inserted between each packet of transport packets read from said buffer is 1 or less.

6. A transmission rate adjustment method for adjusting a transmission rate of a transport stream comprising a plurality of transport packets of a fixed packet length in which encoded data are stored and in which time stamps of a prescribed frequency which is a standard time interval during said encoding are inscribed at fixed time intervals, said transmission rate adjustment method comprising: sequentially writing transport packets of said transport stream to a buffer; anda frequency-dividing system clock of a decoder for decoding said encoded data by a frequency division rate designated by a frequency division rate signal supplied externally, and transmitting transport packets that have been sequentially read from said buffer to said decoder at a transmission rate determined by the frequency-divided system clock, said method further comprising:in writing transport packets to said buffer: detecting time stamps in said transport stream; andupon detecting said time stamps, storing in said buffer: a difference between a first time stamp that is detected this time and a second time stamp that was detected previously, a number of transport packets that exist between the first and second time stamps, and a value of said, second time stamp, as appended information of the transport packet in which said second time stamp is inscribed;in transmitting transport packets to said decoder: upon reading from said buffer a transport packet in which said second time stamp is inscribed, based on said appended information that has been attached to the transport packet, inserting NULL packets between transport packets that have been read from said buffer to implement adjustment such that said transport packets are transmitted at said transmission rate; andwhen adjustment cannot be realized by merely inserting said NULL packets, when reading from said buffer a transport packet to which said first time stamp is inscribed, rewriting the time stamp of said transport packet.

7. A transmission rate adjustment method according to claim 6, wherein, in transmitting transport packets to said decoder, said NULL packets are uniformly inserted between transport packets that are read from said buffer.

8. A transmission rate adjustment method according to claim 7, wherein, in the uniform insertion of said NULL packets: based on the difference between said first and second time stamps and a transmission rate determined by a clock obtained by frequency-dividing said input system clock, calculating a number of transport packets between said first and second time stamps after adjustment of transmission rate, and from a result of this calculation, calculating a number of NULL packets that should be inserted; andwhen a calculation result of dividing said calculated number of NULL packets by said calculated number of transport packets includes a quotient and a remainder, inserting a number of NULL packets that corresponds to said quotient for each transport packet that has been read from said buffer, and further, uniformly inserting a number of NULL packets that corresponds to said remainder in a state in which said NULL packets have been inserted.

9. A transmission rate adjustment method according to claim 7, wherein, in said uniform insertion of said NULL packets: based on the difference between said first and second time stamps and a transmission rate determined by a clock obtained by frequency-dividing said input system clock, calculating a number of transport packets between said first and second time stamps after adjustment of transmission rate, and from a result of this calculation, calculating a number of NULL packets that should be inserted; andwhen a standard average insertion spacing obtained by dividing said calculated number of NULL packets that should be inserted by a number of transport packets that exist between said first and second time stamps is a decimal, taking a value of a whole number portion of this decimal as a first insertion spacing and a value obtained by adding 1 to this value as a second insertion spacing, selecting between said first and second insertion spacing, based on a size relation between the average insertion spacing of NULL packets after NULL packets have been inserted and said standard average insertion spacing, and inserting one NULL packet for transport packets of the number of the value of the selected insertion spacing.

10. A transmission rate adjustment method according to claim 7, wherein the difference between the number of NULL packets that are inserted between each packet of the transport packets that have been read from said buffer is 1 or less.

11. A transmission rate adjustment device for adjusting a transmission rate of an input transport stream, the transmission rate adjustment device taking as input a transport stream that comprises a plurality of transport packets having a fixed packet length in which encoded data are stored, and in which time stamps of a prescribed frequency that is a standard time spacing during said encoding are inscribed at fixed time intervals, said transmission rate adjustment device comprising: a buffer;a buffer write means for both successively writing transport packets of said input transport stream to said buffer and detecting time stamps in said input transport stream; anda buffer read means for taking as input both a frequency division rate signal that designates a frequency division rate and a system clock of a decoder for decoding said encoded data, and for transmitting to said decoder transport packets that have been sequentially read from said buffer at a transmission rate determined by a clock obtained by frequency-dividing the input system clock by a frequency division rate designated by an input frequency division rate signal;wherein:said buffer write means, upon detecting said time stamps, stores in said buffer: a difference between a first time stamp that has been detected this time and a second time stamp that was previously detected, a number of transport packets that exist in an interval between the first and second time stamps, and a value of said second time stamp, as appended information of the transport packet to which said second time stamp is inscribed; andsaid buffer read means, upon reading from said buffer a transport packet to which said second time stamp has been inscribed, based on said appended information that has been attached to the transport packet, inserts NULL packets between transport packets that have been read from said buffer to achieve an adjustment such that said transport packets are transmitted at said transmission rate, and when adjustment cannot be achieved by a mere insertion of NULL packets, when reading from said buffer the transport packet in which said first time stamp has been inscribed, rewrites the time stamp of the transport packet.

12. A transmission rate adjustment method for adjusting a transmission rate of a transport stream composed of a plurality of transport packets of a fixed packet length in which encoded data are stored and in which time stamps of a prescribed frequency which is a standard time interval during said encoding are inscribed at a fixed time intervals, said transmission rate adjustment method comprising: a first step of sequentially writing transport packets of said transport stream to a buffer; anda second step of frequency-dividing a system clock of a decoder for decoding said encoded data by a frequency division rate designated by a frequency division rate signal supplied externally, and transmitting transport packets that have been sequentially read from said buffer to said decoder at a transmission rate determined by the frequency-divided clock;wherein said first step comprises steps of:detecting time stamps in said input transport stream; andupon detecting said time stamps, storing in said buffer: a difference between a first time stamp that is detected this time and a second time stamp that was detected previously, a number of transport packets that exist between the first and second time stamps, and a value of said second time stamp, as appended information of the transport packet in which said second time stamp is inscribed;and said second step comprises steps of:upon reading from said buffer a transport packet in which said second time stamp is inscribed, based on said appended information that has been attached to the transport packet, inserting NULL packets between transport packets that have been read from said buffer to implement an adjustment such that said transport packets are transmitted at said transmission rate; andwhen adjustment cannot be realized by merely inserting said NULL packets when reading from said buffer a transport packet to which said first time stamp is inscribed, rewriting the time stamp of said transport packet.

13. The transmission rate adjustment device of claim 1, wherein said transport stream comprises data in a MPEG2-TS format.

14. A transmission rate adjustment device for a decoder, comprising: a buffer to receive an input transport stream comprising a plurality of input transport packets having a fixed packet length in which encoded data are stored, and in which time stamps of a prescribed frequency that is a standard time interval during said encoding are inscribed at fixed time intervals; anda buffer control unit that sequentially transmits said input transport packets from said buffer to said decoder, at a transmission rate determined by calculating a ratio of a frequency division rate of said input transport stream, as determined by said time stamps of said input transport stream, and a frequency division rate of said decoder, as determined from an input signal from said decoder to said transmission rate adjustment device,said buffer control unit transmitting NULL packets between input transport packets to achieve a transmission rate adjustment required for said decoder as calculated by said ratio.

15. The transmission rate adjustment device of claim 14, wherein said input transport stream comprises data in a MPEG2-TS format.