CN110166724B

CN110166724B - Multimedia data sending method and device based on coaxial cable

Info

Publication number: CN110166724B
Application number: CN201910440936.9A
Authority: CN
Inventors: 瞿军武; 施彦; 薛骏
Original assignee: Wuxi Vimicro Corp
Current assignee: Wuxi Vimicro Corp
Priority date: 2019-05-24
Filing date: 2019-05-24
Publication date: 2021-01-12
Anticipated expiration: 2039-05-24
Also published as: CN110166724A

Abstract

The invention discloses a multimedia data sending method based on a coaxial cable, which comprises the following steps: receiving a multimedia data stream; performing data format conversion on the multimedia data stream to obtain a first data stream; sequentially using the first data packets in the first data stream for cyclic redundancy CRC calculation, and outputting CRC codes according to a preset rule; inserting a CRC code into the first data stream to form a second data stream; generating a time base reference TRS sequence according to a preset protocol; inserting the TRS sequence into the second data stream to form a third data stream; mapping the third data stream into a fourth data stream; each fourth data packet in the fourth data stream is converted to 1-bit serial data. The sending device based on the method comprises the following steps: a data receiving and format converting unit, a CRC calculating and inserting unit, a bit mapping unit and a converting unit. The invention converts the original video data stream and audio data into serial data, and transmits high-definition video and audio data through the coaxial cable, thereby greatly reducing the cost.

Description

Multimedia data sending method and device based on coaxial cable

Technical Field

The invention relates to the field of data transmission, in particular to a multimedia data sending method and device based on a coaxial cable.

Background

At present, the video monitoring market in China is stimulated and pulled by security projects such as safe city construction and the like, and factors such as rapid increase of video monitoring requirements in various industries and the like, so that the ultra-conventional rapid development is achieved, and the overall market scale is rapidly expanded. The analog monitoring system cannot meet the security requirement due to low image definition. And the adoption of the full digital monitoring system brings higher cost of network cable distribution, and is particularly obvious for the reconstruction of monitoring systems of old cells, factory buildings and the like.

The wide application of video monitoring and the increasing digital demand show the trend of replacing the traditional analog system. Conventional surveillance systems are channel coded via composite video signals (CVBS) transmitted over coaxial cable. Because the brightness and the chroma are mixed together, the receiving end is difficult to avoid the mutual crosstalk of the bright colors when decoding the bright color separation, and the image definition is influenced. And the analog system can only transmit standard definition signals and can not meet the requirements of the development of the times. The current popular full digitalization is to use a network camera to transmit high-definition video and audio data through a network cable. However, for the existing traditional monitoring environment, the network cable needs to be replaced, and the cost is increased.

Disclosure of Invention

The invention aims to solve the defects in the prior art.

In order to achieve the purpose, the invention discloses a multimedia data sending method and device based on a coaxial cable.

In one aspect, the method comprises the steps of:

receiving a multimedia data stream; and performing data format conversion on the multimedia data stream to obtain a first data stream, wherein the first data stream is composed of a plurality of first data packets with bit width L.

Sequentially using the first data packets in the first data stream for cyclic redundancy CRC calculation, and outputting a CRC code according to a preset rule, wherein the CRC code consists of a plurality of CRC data packets with bit width L; and inserting the CRC code into the first data stream to form a second data stream, wherein the second data stream is composed of a plurality of second data packets with the bit width L.

Generating a time base reference TRS sequence according to a preset protocol, wherein the TRS sequence is composed of a plurality of TRS data packets with L bit width; inserting the TRS sequence into the second data stream to form a third data stream, wherein the third data stream is composed of a plurality of third data packets with bit width L; and mapping the third data stream into a fourth data stream, wherein the fourth data stream is composed of a plurality of fourth data packets with the bit width W.

Each fourth data packet in the fourth data stream is converted to 1-bit serial data for transmission over the coaxial cable.

Wherein L, W are all positive integers.

In one example, each first data packet is bit-width expanded and then used for CRC calculation according to the data bit width required by a preset CRC calculation formula.

And if the bit width of the initial check code obtained by the CRC calculation is not L, performing data format conversion and/or bit width expansion on the initial check code to obtain a CRC code consisting of a CRC data packet with the bit width of L.

In one example, when a multimedia data stream is received, video data and/or audio data included in the multimedia data stream is obtained.

Also acquiring a horizontal synchronizing signal and a field synchronizing signal contained in the multimedia data stream; when the line synchronization signal and the field synchronization signal are not included in the multimedia data stream, the line synchronization signal and the field synchronization signal are customized according to a predetermined rule.

In one example, a first packet having a bit width L is composed of M-bit video data, a 1-bit line sync signal, a 1-bit field sync signal, and a extension bits, where L is M + a +2, and the extension bits are located at the head position or the end position of the first packet.

Wherein M, A is a positive integer.

In one example, when the row synchronization signal indicates the start of transmission of a row of multimedia data streams, a plurality of first data packets corresponding to the row of multimedia data streams are sequentially used for CRC calculation, and when the row synchronization signal indicates the end of transmission of a row of multimedia data streams, a group of CRC codes consisting of N CRC data packets with bit width L is obtained.

Wherein N is a positive integer.

In one example, a CRC code is inserted into the first data stream during the next system clock cycle in which the row sync signal indicates the end of the transmission of a row of the multimedia data stream to form the second data stream.

In one example, the method further comprises the steps of: and adding M sequences for the line synchronization signal and/or the field synchronization signal, namely adding a preset M sequence at the rising edge and/or the falling edge of the line synchronization signal and/or the field synchronization signal.

When the line synchronizing signal with the M sequence at the falling edge indicates that the transmission of one line of multimedia data stream is finished, inserting CRC codes into the first data stream after a preset time length after the M sequence to form a second data stream.

In one example, the method further comprises the steps of: an asynchronous FIFO is employed to store the second data stream.

In one example, a write operation is performed once during an effective duration of a write signal of the asynchronous FIFO, and N first packets with bit width L in the first data stream are written into the asynchronous FIFO.

When detecting that the line synchronization signal indicates that the transmission of one line of multimedia data stream is finished, prolonging the effective duration of a write signal of the asynchronous FIFO to execute two write operations; the first write operation writes the last 1 to N first data packets corresponding to the line of multimedia data stream into the asynchronous FIFO, and the second write operation writes the last 1 to N CRC data packets corresponding to the line of multimedia data stream into the asynchronous FIFO.

In one example, the second data stream is read from the asynchronous FIFO and one or more sets of TRS sequences are inserted when the asynchronous FIFO is read empty.

In one example, a TRS sequence, comprising:

header data, TRS packet count bit data, and control information data.

When the multimedia data stream contains audio data, the TRS sequence further includes: audio data, audio check bit data, and audio valid bit data.

In one example, the method further comprises the following steps:

and carrying out scrambling processing on the fourth data stream.

And compensating the high-frequency component of the scrambled fourth data stream.

In another aspect, the apparatus comprises:

a data receiving and format converting unit for receiving the multimedia data stream; and performing data format conversion on the multimedia data stream to obtain a first data stream, wherein the first data stream is composed of a plurality of first data packets with bit width L.

The CRC calculation and insertion unit is used for sequentially using the first data packets in the first data stream for CRC calculation and outputting CRC codes according to a preset rule, wherein the CRC codes are formed by a plurality of CRC data packets with L bit width; and inserting the CRC code into the first data stream to form a second data stream, wherein the second data stream is composed of a plurality of second data packets with the bit width L.

The bit mapping unit is used for generating a time base reference TRS sequence according to a preset protocol, wherein the TRS sequence is composed of a plurality of TRS data packets with L bit width; inserting the TRS sequence into the second data stream to form a third data stream, wherein the third data stream is composed of a plurality of third data packets with bit width L; and mapping the third data stream into a fourth data stream, wherein the fourth data stream is composed of a plurality of fourth data packets with the bit width W.

And the conversion unit is used for converting each fourth data packet in the fourth data stream into 1-bit serial data.

In one example, the method further comprises: and the asynchronous FIFO is used for storing the second data stream.

In one example, the method further comprises:

and the scrambling unit is used for scrambling the fourth data stream.

And the pre-emphasis unit is used for compensating the high-frequency component of the scrambled fourth data stream.

The invention has the advantages that: in the conventional monitoring system, original multimedia data is converted into 1-bit serial data in a transmitting device without rewiring. Multimedia data is transmitted through the coaxial cable, thereby greatly reducing costs.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a flow chart of a method for transmitting multimedia data based on a coaxial cable;

FIG. 2 is a block diagram of a multimedia data transmitting apparatus based on coaxial cable;

FIG. 3(a) is a timing diagram of data format conversion according to a first embodiment of the present invention;

FIG. 3(b) is a timing diagram of data format conversion of a row field signal with M sequences according to an embodiment of the present invention;

fig. 4(a) is a schematic diagram of a fourth data packet splicing according to the first embodiment of the present invention;

fig. 4(b) is a schematic diagram of a fourth data packet splicing according to the second embodiment of the present invention;

fig. 4(c) is a schematic diagram of a fourth data packet splicing according to the third embodiment of the present invention;

FIG. 5(a) is a diagram illustrating a third packet storage format in the video asynchronous FIFO according to the first embodiment of the present invention;

FIG. 5(b) is a diagram illustrating a third packet storage format in the video asynchronous FIFO according to the second embodiment of the present invention;

FIG. 5(c) is a diagram illustrating a third packet storage format in the video asynchronous FIFO according to a third embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention discloses a multimedia data transmission method based on a coaxial cable, which is shown in figure 1. The method comprises the following steps:

step S110: receiving a multimedia data stream; and performing data format conversion on the multimedia data stream to obtain a first data stream.

The first data stream is composed of a plurality of first data packets with bit width L.

When the multimedia data stream is received, video data and/or audio data contained in the multimedia data stream are acquired.

Also acquiring a horizontal synchronizing signal HSYNC and a field synchronizing signal VSYNC contained in the multimedia data stream; when the line synchronization signal and the field synchronization signal are not included in the multimedia data stream, the line synchronization signal and the field synchronization signal are customized according to a predetermined rule.

The first packet with bit width L may be formed by M-bit video data, 1-bit line sync signal, 1-bit field sync signal, and a extension bits, where L is M + a +2, the extension bits are located at the head position or the end position of the first packet, and the extension bits are used to separate the first packets.

Step S120: sequentially using the first data packet in the first data stream for cyclic redundancy CRC calculation, and outputting a CRC code according to a preset rule; the CRC code is inserted into the first data stream to form a second data stream.

The CRC code consists of a plurality of CRC data packets with bit width L; the second data stream is composed of a plurality of second data packets having a bit width L.

And according to the data bit width required by a preset CRC calculation formula, performing bit width expansion on each first data packet and then using the data packet for CRC calculation.

And when the line synchronizing signal indicates the transmission start of one line of multimedia data stream, sequentially using a plurality of first data packets corresponding to the line of multimedia data stream for CRC calculation, and when the line synchronizing signal indicates the transmission end of the one line of multimedia data stream, obtaining a group of CRC codes consisting of N CRC data packets with bit width L.

And inserting CRC codes into the first data stream in the next system clock period of which the line synchronization signal indicates the transmission end of one line of multimedia data stream to form a second data stream.

Step S130: generating a time base reference TRS sequence according to a preset protocol; inserting the TRS sequence into the second data stream to form a third data stream; the third data stream is mapped to a fourth data stream.

The TRS sequence consists of a plurality of TRS data packets with bit width L; the third data stream is composed of a plurality of third data packets with bit width L; the fourth data stream is composed of a plurality of fourth data packets having a bit width W.

A TRS sequence comprising: header data, TRS packet count bit data, and control information data.

Step S140: each fourth data packet in the fourth data stream is converted to 1-bit serial data.

In the above steps, L, W, M, A, N are all positive integers. Where M depends on the number of bits of the video data, which is typically 10 bits, 12 bits, 16 bits as conventional video data. A may be set to 1 or other positive integer as desired. N may be based on the number of system operating clocks that need to be occupied to insert the CRC code in the first video stream or on the effective duration of the write signal of the asynchronous FIFO storing the second video stream. The value can be 3 or 4. W is determined according to the transmission bandwidth of the coaxial cable, and if the transmission bandwidth of the coaxial cable, which is currently common, is 20bx74.25mhz ═ 1.485G, W ═ 20. Of course, if only a video signal with a small bandwidth (low definition) is transmitted (e.g., 10bx74.25mhz — 0.7425G, W is 10.

When step S110 is executed, when the obtained multimedia data stream contains a line synchronization signal and a field synchronization signal, in order to enhance the robustness of extracting a line field at the receiving end, an M sequence may be further added to the line synchronization signal and/or the field synchronization signal, that is, a preset M sequence is added at a rising edge and/or a falling edge of the line synchronization signal and/or the field synchronization signal.

In step S120, a step of storing the second data stream using the asynchronous FIFO is further included. The process of inserting a CRC code into the first data stream to form the second data stream is accomplished by means of the asynchronous FIFO.

And executing a write operation once within an effective duration of a write signal of the asynchronous FIFO, and writing N first data packets with bit width L in the first data stream into the asynchronous FIFO.

In performing step S130, the TRS sequence may be inserted into one or more groups when the second data stream is read from the asynchronous FIFO and when the asynchronous FIFO is read empty.

After step S130, the fourth data stream may be scrambled to reduce inter-symbol interference and jitter, so that the receiving end can extract the clock conveniently. And then the high-frequency component of the fourth data stream after scrambling processing is compensated, so that the output signal-to-noise ratio is effectively improved.

In order to implement steps S110 to S140, the present invention discloses a multimedia data transmitting apparatus based on a coaxial cable, as shown in fig. 2. The device includes: a data receiving and format converting unit, a CRC calculating and inserting unit, a bit mapping unit and a converting unit.

A conversion unit, configured to convert each fourth data packet in the fourth data stream into 1-bit serial data.

When the above apparatus is used to transmit data, the apparatus may further include: asynchronous FIFO, scrambling unit and pre-emphasis unit

And the asynchronous FIFO is used for storing the second data stream.

And the scrambling unit is used for scrambling the fourth data stream.

The asynchronous FIFO can also select a video asynchronous FIFO and/or an audio asynchronous FIFO according to the requirement; when both video data and audio data are present, a video asynchronous FIFO may be used to store the second data stream and an audio asynchronous FIFO may be used to store the audio data.

The following describes specific steps of the method and the corresponding apparatus in practical applications by specific embodiments.

Example one

When receiving the multimedia data stream, 10-bit video data, 32-bit audio data, 1-bit line synchronization signal and 1-bit field synchronization signal contained in the multimedia data stream are obtained.

The extension bits are complemented with 0 for 10-bit video data, 1-bit line sync signal, 1-bit field sync signal and 1 extension bit, forming a first data packet of 13 bits, as shown in table 1, where Din [9:0] represents 10-bit video data. The extension bit is used for carrying out data interval when the data packet is merged/spliced subsequently. The extension bit can be set to 1 bit or more bits as required, and the value of the extension bit can be customized.

Bit12

Bit11

Bit10

Bit9

Bit8

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

Din[9]

Din[8]

Din[7]

Din[6]

Din[5]

Din[4]

Din[3]

Din[2]

Din[1]

Din[0]

HSYNC

VSYNC

0

First packet of 113 bits of table

The data bit width required by the CRC calculation formula is set to be 10, and the first data packet is expanded into 20 bits. For example, the extension bit in the first data packet of 13 bits and the 7 bits for calculating the extension are set at the lower bit of the 20-bit data packet and are complemented with 0. The data format is shown in table 2.

Table 2 first packet extended to 20 bits

The specific method of CRC calculation may be implemented by a general technique in the art, and is not particularly limited in the present invention.

In this embodiment, the CRC polynomial edc (x) is used¹⁸+x⁵+x⁴+1, respectively calculating the upper 10 bits and the lower 10 bits of the first data packet expanded into 20 bits to obtain an initial check code. The initial check code includes a CRC packet CRCM [17: 0] of the upper 18 bits]And a CRC packet CRCL [17: 0] of lower 18 bits]。

Since the bit widths of the data packets in the first data stream are all 13 bits, in order to facilitate insertion of the CRC check code, bit width extension and format conversion are performed on the initial check code, so that the bit width of the data packet is the same as the bit width of the first data packet in the first data stream, thereby obtaining a 39-bit CRC code, including 3 CRC data packets with 13 bits, and the methods of bit width extension and format conversion can be set according to actual requirements. In a preferred embodiment, the data structure of the CRC code after bit width expansion and/or format conversion is as follows:

13bx3:{{CRCL[11:0],1′b0},{CRCL[17:12],CRCM[5:0],1′b0},{CRCM[17:6],1′b0}}

the first 13-bit CRC data packet is 12 bits and 1 bit extended bit in the lower 18 bits obtained by CRC calculation, the second 13-bit CRC data packet is 6 bits in the lower 18 bits obtained by CRC calculation, 6 bits in the upper 18 bits and 1 bit extended bit, the third 13-bit CRC data packet is 12 bits and 1 bit extended bit in the upper 18 bits obtained by CRC calculation, and the extended bits are complemented by 0.

In this embodiment, when the row synchronization signal indicates the start of transmission of a row of multimedia data streams, a plurality of first data packets corresponding to the row of multimedia data streams are sequentially used for CRC calculation, and when the row synchronization signal indicates the end of transmission of a row of multimedia data streams, a group of CRC codes consisting of CRC data packets with a bit width of 3 bits being 13 is obtained.

Meanwhile, as shown in fig. 3(a), in the next system clock period when the line synchronizing signal HSYNC indicates the end of the transmission of one line of the multimedia data stream, the CRC code is inserted into the first data stream by means of the video asynchronous FIFO to form the second data stream. The method specifically comprises the following steps:

and executing one-time write operation within an effective duration of a write signal of the video asynchronous FIFO, and writing 1-3 first data packets in the first data stream into the asynchronous FIFO.

When detecting that the line synchronization signal indicates that the transmission of one line of multimedia data stream is finished, prolonging the effective time length of the write signal of the asynchronous FIFO to execute two write operations. And writing 1-3 first data packets at the tail of the line into the asynchronous FIFO in the first writing operation, and writing 1-3 CRC data packets corresponding to the line into the asynchronous FIFO in the second writing operation.

For example, if the multimedia data stream has a line length of 999, i.e. a line length of 999 first packets, 3 CRC packets are inserted at the end of the line. To facilitate CRC packet insertion, the first data stream is written into the asynchronous FIFO in 3 first packet combinations at a time. Then, a write operation is performed to write the 3-bit wide 13 first data packets in the first data stream into the asynchronous FIFO within an effective duration of the write signal of the video asynchronous FIFO. In this embodiment, an effective duration of the write signal of the video asynchronous FIFO is one system clock period. When detecting that the line synchronization signal indicates that the transmission of one line of multimedia data stream is finished, prolonging the effective duration of the write signal of the video asynchronous FIFO to two system clock periods so as to execute two write operations. The first writing operation writes the last 3 first data packets at the tail of the line into the video asynchronous FIFO, and the second writing operation writes the 3 CRC data packets corresponding to the line into the video asynchronous FIFO at one time.

If the multimedia data stream has a line length of 1000, a line is 1000 first packets. The end of the line inserts 3 CRC packets. Then, when inserting CRC packets, the first write writes 1 first packet and 2 CRC packets at the end of the line into the asynchronous FIFO, and the second write writes 1 CRC packet at the end of the line into the asynchronous FIFO.

The timing reference TRS sequence is typically used to transmit synchronization signals, control signals, etc., associated with the multimedia data stream. In this embodiment, when the time-base reference TRS sequence is generated, 32-bit audio data is read from the audio asynchronous FIFO and written into the TRS data packet, in this embodiment, a set of TRS sequences including 6 TRS data packets with 13 bits is specified by a preset protocol, as shown in table 3.

TABLE 3 TRS sequences

Wherein TRS _ HEAD is 2 pieces of 13-bit header data, and TRS _ INFO is 4 pieces of 13-bit information data.

The header data is used to locate the TRS packet and to distinguish it from the video data.

In the information data, AUD _ L is left channel 16-bit data, AUD _ R is right channel 16-bit data, PN _ L/P _ L is left channel data parity check bit, PN _ R/P _ R is right channel data parity check bit, AUD _ VALID is audio data VALID bit, ctrl _ info is control information, and cnt is TRS packet count bit.

The TRS sequence is inserted into one or more groups when the second data stream is read from the asynchronous FIFO and when the asynchronous FIFO is read empty. As a preferred embodiment, 4 sets may be inserted at a time, marked with cnt (0 to 3), until the video asynchronous FIFO is not empty. Thus, when the receiving end determines that at least 2 sets of correct TRS sequences are received according to the cnt value, the receiving end can think that the correct TRS sequences are found.

A third data stream consisting of 13-bit data packets is mapped to a fourth data stream consisting of 20-bit data packets.

Wherein, the lower 7 bits of the first 13-bit data packet and the second 13-bit data packet form a first 20-bit data packet, the upper 6 bits of the second 13-bit data packet, the lower 1 bit of the third 13-bit data packet and the fourth 13-bit data packet form a second 20-bit data packet, the upper 12 bits of the fourth 13-bit data packet and the lower 8 bits of the fifth 13-bit data packet form a third 20-bit data packet, and so on. As shown in fig. 4 (a). It will be appreciated by those skilled in the art that this mapping method is merely a preferred embodiment, and that various other mapping methods may be used in the implementation.

Example two

When receiving the multimedia data stream, 12-bit video data, 32-bit audio data, 1-bit line synchronization signal and 1-bit field synchronization signal contained in the multimedia data stream are obtained.

The extension bits are complemented with 0 for 12-bit video data, 1-bit line sync signal, 1-bit field sync signal and 1 extension bit, forming a first data packet of 15 bits, as shown in table 4, where Din [11:0] represents 12-bit video data. The extension bit is used for carrying out data interval when the data packet is merged/spliced subsequently. The extension bit can be set to 1 bit or more bits as required, and the value of the extension bit can be customized.

Bit14

Bit13

Bit12

Bit11

Bit10

Bit9

Bit8

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

Din[11]

Din[10]

Din[9]

Din[8]

Din[7]

Din[6]

Din[5]

Din[4]

Din[3]

Din[2]

Din[1]

Din[0]

HSYNC

VSYNC

0

First packet of 415 bits of table

The data bit width required by the CRC calculation formula is set to be 10, and the first data packet is expanded into 20 bits. For example, the extension bit in the first data packet of 15 bits and 5 bits for calculating the extension are set at the lower bit of the 20-bit data packet and are complemented with 0. The data format is shown in table 5.

Table 5 first packet extended to 20 bits

Because the bit width of the data packet in the first data stream is 15 bits, in order to facilitate insertion of the CRC check code, bit width expansion and format conversion are performed on the initial check code, so that the bit width of the data packet is the same as the bit width of the first data packet in the first data stream, thereby obtaining a 45-bit CRC code, including 3 CRC data packets with 15 bits, and the methods of bit width expansion and format conversion can be set according to actual requirements. In a preferred embodiment, the data structure of the CRC code after bit width expansion and/or format conversion is as follows:

15bx3:{{CRCL[11:0],3′b0},{CRCL[17:12],CRCM[5:0],3′b0},{CRCM[17:6],3′b0}}

the first 15-bit CRC data packet is 12 bits and 3 extended bits of the lower 18 bits obtained by CRC calculation, the second 15-bit CRC data packet is 6 bits of the lower 18 bits obtained by CRC calculation, 6 bits and 3 extended bits of the upper 18 bits obtained by CRC calculation, the third 15-bit CRC data packet is 12 bits and 3 extended bits of the upper 18 bits obtained by CRC calculation, and the extended bits are complemented by 0.

In this embodiment, when the row synchronization signal indicates the start of transmission of a row of multimedia data streams, a plurality of first data packets corresponding to the row of multimedia data streams are sequentially used for CRC calculation, and when the row synchronization signal indicates the end of transmission of a row of multimedia data streams, a group of CRC codes consisting of CRC data packets with a bit width of 3 bits being 15 is obtained.

For example, if the multimedia data stream has a line length of 999, i.e. a line length of 999 first packets, 3 CRC packets are inserted at the end of the line. To facilitate CRC packet insertion, the first data stream is written into the asynchronous FIFO in 3 first packet combinations at a time. Then, a write operation is performed to write the first data packet with the bit width of 3 bits in the first data stream as 15 into the asynchronous FIFO within an effective duration of the write signal of the video asynchronous FIFO. In this embodiment, an effective duration of the write signal of the video asynchronous FIFO is one system clock period. When detecting that the line synchronization signal indicates that the transmission of one line of multimedia data stream is finished, prolonging the effective duration of the write signal of the video asynchronous FIFO to two system clock periods so as to execute two write operations. The first writing operation writes the last 3 first data packets at the tail of the line into the video asynchronous FIFO, and the second writing operation writes the 3 CRC data packets corresponding to the line into the video asynchronous FIFO at one time.

The timing reference TRS sequence is typically used to transmit synchronization signals, control signals, etc., associated with the multimedia data stream. In this embodiment, when the time-base reference TRS sequence is generated, 32-bit audio data is read from the audio asynchronous FIFO and written into the TRS data packet, in this embodiment, a set of TRS sequences including 6 TRS data packets with 15 bits is defined by a preset protocol, as shown in table 6.

TABLE 6 TRS sequences

Wherein TRS _ HEAD is 2 pieces of 15-bit header data, and TRS _ INFO is 4 pieces of 15-bit information data.

The TRS sequence is inserted into one or more groups when the second data stream is read from the asynchronous FIFO and when the asynchronous FIFO is read empty. As a preferred embodiment, 6 sets may be inserted at a time, marked with cnt (0 to 5) until the video asynchronous FIFO is not empty. Thus, when the receiving end determines that at least 3 sets of correct TRS sequences are received according to the cnt value, the receiving end can think that the correct TRS sequences are found.

A third data stream consisting of 15-bit data packets is mapped to a fourth data stream consisting of 20-bit data packets.

Wherein, the low 5 bits of the first 15-bit data packet and the second 15-bit data packet form a first 20-bit data packet, the high 10 bits of the second 15-bit data packet and the low 10 bits of the third 15-bit data packet form a second 20-bit data packet, and the high 5 bits of the third 15-bit data packet and the fourth 15-bit data packet form a third 20-bit data packet. As shown in fig. 4 (b). It will be appreciated by those skilled in the art that this mapping method is merely a preferred embodiment, and that various other mapping methods may be used in the implementation.

EXAMPLE III

When receiving the multimedia data stream, 16-bit video data, 32-bit audio data, 1-bit line synchronization signal and 1-bit field synchronization signal contained in the multimedia data stream are obtained.

The extension bits are complemented with 0 for 16-bit video data, 1-bit line sync signal, 1-bit field sync signal and 1 extension bit, forming a 19-bit first packet, as shown in table 7, where Din [15:0] represents 16-bit video data. The extension bit is used for carrying out data interval when the data packet is merged/spliced subsequently. The extension bit can be set to 1 bit or more bits as required, and the value of the extension bit can be customized.

Bit18

Bit17

Bit16

Bit15

Bit14

Bit13

Bit12

Bit11

Bit10

Bit9

Bit8

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

Din [15]

Din [14]

Din [13]

Din [12]

Din [11]

Din [10]

Din [9]

Din [8]

Din [7]

Din [6]

Din [5]

Din [4]

Din [3]

Din [2]

Din [1]

Din [0]

HSYNC

VSYNC

0

First packet of table 719 bits

The data bit width required by the CRC calculation formula is set to be 10, and the first data packet is expanded into 20 bits. For example, the extension bit in the first data packet of 19 bits and 1 bit for calculating the extension are set at the lower bit of the 20-bit data packet and are complemented with 0. The data format is shown in table 8.

Table 8 first packet extended to 20 bits

Since the bit widths of the data packets in the first data stream are all 19 bits, in order to facilitate insertion of the CRC check code, bit width extension and format conversion are performed on the initial check code, so that the bit width of the data packet is the same as the bit width of the first data packet in the first data stream, thereby obtaining a 57-bit CRC code, including 3 CRC data packets with 19 bits, and the methods of bit width extension and format conversion can be set according to actual requirements. In a preferred embodiment, the data structure of the CRC code after bit width expansion and/or format conversion is as follows:

19bx3:{{CRCL[11:0],7′b0},{CRCL[17:12],CRCM[5:0],7′b0},{CRCM[17:6],7′b0}}

the first 19-bit CRC data packet is 12 bits and 7-bit extended bits in the lower 18 bits obtained by CRC calculation, the second 19-bit CRC data packet is 6 bits in the lower 18 bits obtained by CRC calculation, and 6 bits and 7-bit extended bits in the upper 18 bits obtained by CRC calculation, and the third 19-bit CRC data packet is 12 bits and 7-bit extended bits in the upper 18 bits obtained by CRC calculation, wherein the extended bits are complemented by 0.

In this embodiment, when the row synchronization signal indicates the start of transmission of a row of multimedia data streams, a plurality of first data packets corresponding to the row of multimedia data streams are sequentially used for CRC calculation, and when the row synchronization signal indicates the end of transmission of a row of multimedia data streams, a group of CRC codes consisting of CRC data packets with a bit width of 3 bits of 19 is obtained.

For example, if the multimedia data stream has a line length of 999, i.e. a line length of 999 first packets, 3 CRC packets are inserted at the end of the line. To facilitate CRC packet insertion, the first data stream is written into the asynchronous FIFO in 3 first packet combinations at a time. Then, a write operation is performed to write the first packet with the bit width of 3 bits in the first data stream as 19 into the asynchronous FIFO within an effective duration of the write signal of the video asynchronous FIFO. In this embodiment, an effective duration of the write signal of the video asynchronous FIFO is one system clock period. When detecting that the line synchronization signal indicates that the transmission of one line of multimedia data stream is finished, prolonging the effective duration of the write signal of the video asynchronous FIFO to two system clock periods so as to execute two write operations. The first writing operation writes the last 3 first data packets at the tail of the line into the video asynchronous FIFO, and the second writing operation writes the 3 CRC data packets corresponding to the line into the video asynchronous FIFO at one time.

The timing reference TRS sequence is typically used to transmit synchronization signals, control signals, etc., associated with the multimedia data stream. In this embodiment, when the time-base reference TRS sequence is generated, 32-bit audio data is read from the audio asynchronous FIFO and written into the TRS data packet, and in this embodiment, a set of TRS sequences including 6 TRS data packets with 19 bits is defined by a preset protocol, as shown in table 9.

TABLE 9 TRS sequences

Wherein TRS _ HEAD is 2 pieces of 19-bit header data, and TRS _ INFO is 4 pieces of 19-bit information data.

A third data stream consisting of 19-bit data packets is mapped to a fourth data stream consisting of 20-bit data packets.

Wherein, the lower 1 bit of the first 19-bit data packet and the second 19-bit data packet forms the first 20-bit data packet, the upper 18 bit of the second 19-bit data packet and the lower 2 bit of the third 19-bit data packet form the second 20-bit data, the upper 17 bit of the third 19-bit data packet and the lower 3 bit of the fourth 19-bit data packet form the third 20-bit data, and so on. As shown in fig. 4 (c). It will be appreciated by those skilled in the art that this mapping method is merely a preferred embodiment, and that various other mapping methods may be used in the implementation.

Example four

When receiving the multimedia data stream, 16-bit video data and 32-bit audio data contained in the multimedia data stream are obtained.

At this time, the line synchronizing signal and the field synchronizing signal do not exist, and the 1-bit line synchronizing signal and the 1-bit field synchronizing signal are customized.

The extended bits are complemented with 0 for 16-bit video data, 1-bit line sync signal, 1-bit field sync signal, and 1 extended bit, to form a 19-bit first packet.

The subsequent steps are the same as those in the third embodiment, and are not described herein again.

The following steps may also be performed for the above embodiments one, two, three, and four.

In order to enhance the robustness of extracting line fields at a receiving end, the interference on signals in transmission is reduced. And adding M sequences for the line synchronization signal and the field synchronization signal, namely adding preset M sequences at the rising edge and the falling edge of the line synchronization signal and the field synchronization signal. In a preferred embodiment, adding a predetermined M-sequence at the rising edge and/or the falling edge is to change the signal 1 after the rising edge or the signal 0 after the falling edge to the value of the M-sequence, such as 16-bit binary code 0001101101011001.

And for the line synchronizing signal with the M sequence at the falling edge, when the line synchronizing signal indicates the transmission end of one line of multimedia data stream, and after a preset time length after the M sequence, such as 2, 3 or 4 system clock periods, inserting a CRC code into the first data stream to form a second data stream. As shown in fig. 3(b), HSYNC _ map indicates a line synchronization signal having an M sequence; VSYNC _ map represents a field sync signal having an M sequence; m sequence denotes an M sequence.

In order to reduce intersymbol interference and jitter, the clock extraction of a receiving end is facilitated. Using the formula G (x) ═ x⁹+x⁴+1 the fourth data stream is scrambled.

In order to obtain a better signal waveform at the receiving end, the damaged signal is compensated, that is, the fourth data stream after scrambling is subjected to pre-emphasis processing. To reduce the ISI caused by the high frequency attenuation of the coaxial cable.

In the above embodiments one, two, three, and four, the video asynchronous FIFO with the size of 32X57b and the operation clock of 74.25MHz can be used. In the first embodiment, the storage format of the 13-bit third data stream in the video asynchronous FIFO is as shown in fig. 5 (a); in the second embodiment, the storage format of the 15-bit third data stream in the video asynchronous FIFO is shown in fig. 5 (b); in the third embodiment, the storage format of the 19-bit third data stream in the video asynchronous FIFO is shown in fig. 5 (c); wherein the shaded cells indicate written data and the blank cells indicate unwritten data.

In the above embodiments one, two, three, and four, the audio asynchronous FIFO with the size of 8X32b, the write clock of 3.072MHz, and the read clock of 74.25MHz can be used.

The embodiment provides a multimedia data sending device and method based on a coaxial cable. In the conventional monitoring system, the original video data stream and audio data are converted into 1-bit serial data in the transmitting device without rewiring. High-definition video and audio data are transmitted through the coaxial cable, so that the cost is greatly reduced.

The above embodiments are provided to further explain the objects, technical solutions and advantages of the present invention in detail, it should be understood that the above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A multimedia data transmission method based on coaxial cable is characterized by comprising the following steps:

receiving a multimedia data stream, and acquiring video data, a line synchronization signal and a field synchronization signal contained in the multimedia data stream; performing data format conversion on the multimedia data stream to obtain a first data stream, wherein the first data stream is composed of a plurality of first data packets with bit width L; the first data packet with the bit width of L consists of M-bit video data, a 1-bit line synchronizing signal, a 1-bit field synchronizing signal and A extension bits, wherein L is M + A + 2;

sequentially using the first data packets in the first data stream for cyclic redundancy CRC calculation, and outputting a CRC code according to a preset rule, wherein the CRC code is composed of a plurality of CRC data packets with L bit width; inserting the CRC code into the first data stream to form a second data stream, wherein the second data stream is composed of a plurality of second data packets with bit width L;

generating a time base reference TRS sequence according to a preset protocol, wherein the TRS sequence is composed of a plurality of TRS data packets with L bit width; inserting the TRS sequence into a second data stream to form a third data stream, wherein the third data stream is composed of a plurality of third data packets with bit width L; mapping the third data stream into a fourth data stream, wherein the fourth data stream is composed of a plurality of fourth data packets with bit width W; the bit width W of the fourth data packet is determined according to the transmission bandwidth of the coaxial cable;

converting each fourth data packet in the fourth data stream into 1-bit serial data for transmission over a coaxial cable;

wherein L, W, M, A are all positive integers.

2. The method according to claim 1, wherein according to the data bit width required by the preset CRC calculation formula, each first data packet is subjected to bit width expansion before being used for CRC calculation;

3. The method of claim 1, wherein the horizontal sync signal and the field sync signal are customized according to a predetermined rule when the horizontal sync signal and the field sync signal are not included in the multimedia data stream.

4. The method of claim 1, wherein the extension bit is located at a first position or a last position of the first packet.

5. The method according to claim 1 or 3, wherein when the line synchronization signal indicates the beginning of transmission of a line of multimedia data stream, the plurality of first packets corresponding to the line of multimedia data stream are sequentially used for CRC calculation, and when the line synchronization signal indicates the end of transmission of a line of multimedia data stream, a set of CRC codes consisting of N CRC packets with bit width L is obtained;

wherein N is a positive integer.

6. A method according to claim 1 or 3, wherein the second data stream is formed by inserting a CRC code into the first data stream in the next system clock cycle in which the line synchronisation signal indicates the end of transmission of a line of the multimedia data stream.

7. A method according to claim 1 or 3, further comprising the step of: adding M sequences for the line synchronization signal and/or the field synchronization signal, namely adding a preset M sequence at the rising edge and/or the falling edge of the line synchronization signal and/or the field synchronization signal;

8. The method of claim 1, further comprising the step of: and storing the second data stream by adopting an asynchronous FIFO.

9. The method according to claim 8, wherein a write operation is performed to write N first packets with bit width L in the first data stream into the asynchronous FIFO for an effective duration of a write signal of the asynchronous FIFO;

10. The method of claim 8, wherein the second data stream is read from the asynchronous FIFO and one or more sets of TRS sequences are inserted when the asynchronous FIFO is empty.

11. The method of claim 1, wherein the TRS sequence comprises:

header data, TRS packet count bit data, and control information data;

when receiving the multimedia data stream, the method also acquires audio data contained in the multimedia data stream;

12. The method of claim 1, further comprising the steps of:

scrambling the fourth data stream;

13. A multimedia data transmitting apparatus based on a coaxial cable, comprising:

a data receiving and format converting unit for receiving the multimedia data stream; performing data format conversion on the multimedia data stream to obtain a first data stream, wherein the first data stream is composed of a plurality of first data packets with bit width L;

a CRC calculation and insertion unit, configured to sequentially use a first data packet in the first data stream for CRC calculation, and output a CRC code according to a predetermined rule, where the CRC code is formed by multiple CRC data packets with a bit width of L; inserting the CRC code into the first data stream to form a second data stream, wherein the second data stream is composed of a plurality of second data packets with bit width L;

the bit mapping unit is used for generating a time base reference TRS sequence according to a preset protocol, wherein the TRS sequence is composed of a plurality of TRS data packets with L bit width; inserting the TRS sequence into a second data stream to form a third data stream, wherein the third data stream is composed of a plurality of third data packets with bit width L; mapping the third data stream into a fourth data stream, wherein the fourth data stream is composed of a plurality of fourth data packets with bit width W;

14. The apparatus of claim 13, further comprising:

and the asynchronous FIFO is used for storing the second data stream.

15. The apparatus of claim 13, further comprising:

a scrambling unit, configured to perform scrambling processing on the fourth data stream;