1. Field of the Invention
The present invention relates to a data switching apparatus used in transmission or broadcasting apparatuses for selecting and transmitting the data from a plurality of received data without changing coding unit.
2. Description of the Prior Art
FIG. 16 shows a conventional data switching apparatus provided in a TV studio for example. In FIG. 16, received data 110A and 110B are TV signals (NTSC signals and so on) input to the present apparatus. The received data 110A and 110B include information such as a vertical drive pulse which shows a frame (synchronization). The conventional data switching apparatus also include frame detectors 101A, 101B, and switches 102A, 102B. The switches 102A and 102B respectively turn ON/OFF the received data 110A and 110B at the timing from the frame detectors 101A and 101B under the control of a control unit 103. The control unit 103 controls either of switches 102A and 102B to turn ON/OFF by an external switching request (not shown).
The operation is explained below. A plurality of received data 110A and 110B input into the present apparatus are TV signals including synchronization signals. The timing of the synchronization signals is controlled so that respective timings of the received data 110A and 110B are the same.
The frame detectors 101A and 101B detect frames (synchronization signal) such as a vertical driving pulse of the received data and provides them to the switches 102A and 102B. This frame represents the head of the data defining the TV image. The control unit 103 instructs either of the switches 102A and 102B to be ON and the other to be OFF.
The switches 102A and 102B are switched by the instruction of the control unit 103 according to the frame timing of the frame detectors 101A and 101B. Since the frames of a plurality of received data 110A and 110B are all synchronized, the timing provided from the frame detectors 101A and 101B to the switches 102A and 102B are all synchronized. Therefore, the respective switches 102A and 102B are switched at the same time. At this time, only one switch turns ON and the other turns OFF.
In this way, the present apparatus always selects one data stream from a plurality of received data. In FIG. 16, only two pairs of frame detector 101A and switch 102A, and frame detector 101B and switch 102B are shown for simplicity of explanation. But, the data switching apparatus of FIG. 16 may have plural pairs of the frame detectors and switches. Since the switches 102A and 102B are switched at the head of the frame upon selecting the data, the frame of the data at the vicinity of switching point can be held in a constant period.
Therefore, the data switched by this apparatus does not have bad influence to the image due to switching such as a image turbulence (noise) and a step-out of the frame synchronization, and therefore, the image can be kept in the same as a state without switching the data.
As explained above, the conventional switching apparatus has been necessary to meet frames of all data for each frame according to an externally applied clock. Accordingly, there is a problem in that the conventional switching apparatus cannot process the data whose respective frame timings are not synchronized.
Moreover, since the frame periods of all received data must be the same, the conventional apparatus cannot process the data if the received data is encoded with a variable length code.
It is an object of the present invention to provide a data switching apparatus which links any data at any point when it switches data.
It is another object of the present invention to provide a data switching apparatus which links the data without breaking the data.
It is a further object of the present invention to provide a data switching apparatus which operates normally even if the data unit detector delays in detecting the data unit.
It is a still further object of the present invention to provide a data switching apparatus which discards the undesired data by replacing undesired data with invalid data.
It is a further object of the present invention to provide a data switching apparatus which decreases the video buffer remaining quantity in the decoder to prevent the buffer from overflowing.
It is a further object of the present invention to provide a data switching apparatus which increases the video buffer remaining quantity in the decoder to prevent the buffer from underflowing.
It is a further object of the present invention to provide a data switching apparatus which holds the video buffer remaining quantity in the decoder to prevent the buffer from overflowing and underflowing.
It is a further object of the present invention to provide a data switching apparatus which increases the switching points for switching the data normally.
According to one aspect of the invention, a data switching apparatus includes plural data unit detectors each for detecting a coding unit of a data from a received data; plural data storages each for storing a received data in a buffer and transmitting the received data at a given time from a point specified by the data unit detector; and a data selecting unit for selecting and transmitting only one data stream from a plurality of data streams which are transmitted respectively from the plural data storages.
According to another aspect of the invention, in the data switching apparatus, the data storage starts and terminates the data transmission at the end of the coding unit in the data detected by the data unit detector; and the data selecting unit switches the data streams from the data storage so that each of the data stream from respective data storage is linked together in a continuous data stream.
According to other aspect of the invention, in the data switching apparatus, each respective storage include a delay unit which delays the received data for more than a predetermined time.
According to further aspect of the invention, the data switching apparatus further includes a pattern generator for transmitting a predetermined data pattern to the data selecting unit upon request from the data selecting unit.
According to further aspect of the invention, in the data switching apparatus, the pattern generator generates and transmits invalid data, that is, data quantity requested by the data selecting unit.
According to further aspect of the invention, in the data switching apparatus, the pattern generator generates and transmits data quantity requested by the data selecting unit and stuff data for video data.
According to further aspect of the invention, in the data switching apparatus, the pattern generator generates and transmits data quantity requested by the data selecting unit and unit coding video data with small information quantity.
According to further aspect of the invention, the data switching apparatus further includes a comparator for comparing each value of respective decoding start delay time included in two received data to be switched, wherein the data selecting unit inserts stuff data in the video data when the decoding start delay time before switching is larger than that after switching, and inserts unit coding video data with a small information quantity in the video data when the decoding start delay time before switching is smaller than that after switching, so that the respective decoding start delay times included in the two received data to be switched become the same.
According to further aspect of the invention, a data switching apparatus includes plural data unit detectors each for detecting a coding unit of received data; plural data storages each for storing a received data in a buffer and transmitting the received data specified from the data unit detector at a given time from a point specified by the data unit detector; and a multiplexer for multiplexing and transmitting any numbers of data streams from a plurality of data streams which are transmitted respectively from the plural data storages.
According to further aspect of the invention, the data switching apparatus further includes a pattern generator for transmitting a predetermined data pattern to the multiplexer upon request from the multiplexer.
According to further aspect of the invention, the data switching apparatus further includes a pattern generator for transmitting a predetermined data pattern to the multiplexer upon request from the multiplexer.
According to further aspect of the invention, the data switching apparatus further includes plural switching notifiers each for notifying originators for receiving data to be switched of an advance and completion notices for switching the data in response to the request from the data selecting unit upon switching.
According to further aspect of the invention, the switching notifier requests the transmission data source to generate breaking points for the data coding unit frequently.