Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Patent
1998-04-23
2000-10-03
Patel, Ajit
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
370464, H04J 316
Patent
active
061283169
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a transmitting apparatus transmitting video and audio signals between digital video/audio apparatuses, acquiring a part of a bandwidth of a transmitting medium before communication.
TECHNICAL BACKGROUND
There is standardization for a bandwidth compression system of a digital video signal and a digital audio signal. The system is called MPEG (Moving Picture Experts Group) and is divided into two groups, MPEG1 subject to storage media at a low rate and MPEG2 which realizes a high picture quality for broadcast and can correspond to different picture sizes. In MPEG2, because compression ratio is variable for a picture size or a required picture quality, the data size per time is variable for broadcast programs and contents.
Further, in MPEG2, standardization is also proceeded for data transmission system used for broadcast. In this transmission system, one program is called stream and the data size is variable in each stream (variable rate) and a system to transmit a plurality of streams all together is standardized. Especially, in the case in which a reproducing apparatus to reproduce compressed video audio signals has to isochronize with the broadcast station which makes compression, like in a case to receive a broadcast wave, a stream called transport stream is used. In this transport stream, a device to make the reproducing apparatus possible to isochronize is included, using a parameter in the stream. In the transport stream, the data is transmitted with a fixed length packet (transport stream packet, hereafter) and data necessary for isochronization is also transmitted with the same kind of packet. It is described in a reference, coding of moving picture and associated audio information Part 1, System" of ISO/IEC International Standard 13818-1, International Technology.
In the case of transmitting a plurality of streams, it is possible to vary the data size per stream if necessary although the bandwidth of the entire transmission medium is fixed. It is possible to effectively use the bandwidth of the determined transmission medium by allocating a broad bandwidth to a stream which a high rate is required and suppressing the rates of the other streams, not equally sharing the bandwidth of the entire transmission medium to each stream.
On the other hand, in the case in which broadcast signal is once received, a specific stream is selected and is transmitted or recorded again, a bandwidth for transmission or recording has to be secured on the basis of the maximum rate in the selected stream. For such a purpose, a method indicating a buffer for smoothing a stream (smoothing buffer, hereafter) and a bandwidth necessary for transmission or recording with a reading rate from the smoothing buffer (leak rate, hereafter) is adopted in MPEG2. The smoothing buffer memory size and the leak rate are shown by parameters included in the stream.
In the method using smoothing buffer and leak rate, the received stream is once stored in a smoothing buffer memory and is read from here at the leak rate. As long as a smoothing buffer memory having a size expressed by a parameter in the stream and a leak rate are used, the smoothing buffer memory is guaranteed not to overflow. Therefore, in the case of being transmitted or recorded again, transmission or recording becomes possible by securing the bandwidth equal to the leak rate. Because by once smoothing the rate, it becomes unnecessary to secure the bandwidth equal to the maximum rate which rarely occurs, the bandwidth at transmitting or recording the stream with a variable rate can be minimum and it is possible to effectively use a transmitting medium or recording medium.
However, because timing information of each transport stream packet is deteriorated by once storing the stream in a smoothing buffer memory, the reproducing apparatus of video and audio signals cannot isochronize. Therefore, in the case of transmission or recording, timing information written in the smoothing buffer memory is added to each packet. On the o
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Japanese language search report for International Appln. No. PCT/JP96/01123.
English translation of Japanese language search report for International Appln. No. PCT/JP96/01123.
Iitsuka Hiroyuki
Nishimura Takuya
Takeda Hidetoshi
Yamada Masazumi
Matsushita Electric - Industrial Co., Ltd.
Patel Ajit
Pizarro Ricardo M.
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