1 introduction

In the process of transitioning from analog television to digital television, digital broadcasting is at the forefront. In recent years, the successful application of systems such as automatic broadcasting of advertising program hard drives and automatic broadcasting of news program hard drives in many television stations, especially the rapid development of video compression technology, large capacity storage technology, and transmission technology, has made the establishment of a digital television hard drive broadcasting system based on hard drive storage recognized in the industry and is gradually being promoted and applied. Our fully digital hard disk broadcasting system has undergone more than a year of technical personnel inspection, demonstration, installation and debugging. It was officially put into use at the end of 2001 and has been operating reliably ever since.

2、 System requirements

The digitization of the broadcasting system is an important part of the overall digitization of the television system. Our broadcasting system needs to broadcast 2-4 sets of TV programs. Therefore, in addition to the basic requirement of safety and reliability for the hard disk broadcasting system, the centralized broadcasting of multiple programs requires high requirements for the system's storage capacity, the number of program input and output channels, data transmission speed, and data read and write speed. When designing this fully digital broadcasting system, we first considered the following requirements:

1. The system supports multi-channel broadcasting. Realize hard disk broadcasting of two sets of self-produced programs, and can be expanded to hard disk broadcasting of all four sets of self-produced programs after merging with cable stations.

2. The broadcast adopts MPEG-2 (4:2:2) format to transmit and store program signals, and uses 8Mb/s-12Mb/s bitstream for encoding.

3. All internal systems use SDI digital signals (embedded with AES/EBU standard audio).

4. To ensure system security, the main components of the system, such as the hard disk server, matrix, and playback control machine, are designed with backups that work simultaneously with the host and can be switched at any time.

5. The system interface is concise and intuitive, and the operating platform adopts the Windows NT Chinese system. The operation should be simple, with minimal input, comprehensive functionality, and safety and reliability.

3、 Hardware system design

The core equipment of the digital hard disk broadcasting system is a high-performance hard disk server with large storage capacity, wide basic bandwidth, and multiple input and output channels. Multiple output channels share data from the video storage server, and multiple video servers are connected through Fiber Channels.

Our system design is centered around the hard drive and matrix, with all internal signals using SDI and external signals using SDI and analog composite coexisting forms. Based on this, all relevant equipment adopts digital format, and the hard disk server uses 2 PROFILE PVS1024720G RAID3 hard disks, which can store about 100 hours of high-quality TV programs in MPEG2 compressed format. The digital matrix uses UK QUARTZ products. The system diagram is shown in Figure 1.

1. Program upload: Our station currently broadcasts videos in DVCPRO50, MII, BetaCam, and U-matic formats. The design uses 4 types of models with 2 each and 4 signals from the main control matrix as the upload source signal. Among the four models, except for DVCPRO50, M Ⅱ and BetaCam are directly connected through GVG 8950 ADC component type AD conversion and then connected through Miranda AMX-10i audio embedding. U-matic can only be connected through GVG 8960DEC composite AD conversion and Miranda AMX-10i audio embedding due to no component output; The four signals from the overall control matrix are originally SDI and only need to be synchronized through GVG 8981 frames before being connected. After matrix switching, the source signal enters the four input ports of PVS1024 for encoding, compression into MPEG-2 format, and storage on the hard drive.

2. Program broadcasting: The system operates in parallel with two sets of video servers, the main and backup, which are completely mirrored. Once the main video server fails, it switches to the backup video server to continue broadcasting. Emergency broadcasting can achieve synchronous switching without delay. All process detection and control are completed in real-time by the broadcast control machine.

The 8-way output feedback matrix of the hard drive is used for more convenient and flexible calling. The test card generator is digital, and only needs to be embedded in the CD player audio through Miranda AMX-10i before connecting to the matrix. The hard disk output, external signals, and test cards are all controlled by the broadcast control computer and broadcasted in the order of the program list.

Our switching station uses QUARTZ QMC, which mainly plays a key mixing role. Its 4-way switching source is PGM PST、EMERGNCY、BYPASS， PST can pre monitor the content on the key. Its two keys both have soft switching function, which can be controlled by software up and down. After being connected to the matrix through Q-Link, the source signal of the matrix can be directly called, which is equivalent to a backup of the matrix control panel. Two keys are used to control the logo and subtitles respectively. QMC has a unique two-level backup, PGM and PST come from the main matrix, EMERGENCY comes from the self prepared matrix, which can be used when there is a problem with the main matrix or maintenance is needed. The BYPASS signal also comes from the self prepared matrix, which can completely bypass QMC switching. QMC can also accept embedded and digital audio, and the volume can be manually and controlled by broadcasting software. PGM and PST come from the main matrix, while EMERGNCY and BYPASS come from their own matrices. Delete this sentence)

This system (to be supplemented by your company based on actual usage) will be outputted.

The signal allocation of this system uses GVG 8941, 8931, and 89208941 with analog output, which can be used for signal monitoring; Choose WHOLER AMP2VSA for sound monitoring, which can directly receive digital audio. The analog output part uses a GVG 8960DEC DA converter and Miranda ADX-10i audio output after de embedding.

This system equipment is supplied and integrated by Yongda International Technology Co., Ltd. Due to the strong technical strength of the company and the rich experience accumulated in various system integration projects both domestically and internationally, this system has reached the most advanced level in equipment and installation technology abroad.

4、 Software system design

Software is one of the important components of the entire system. After the selection of high-quality and reliable hardware equipment, the progressiveness, reliability, broadcast quality and broadcast effectiveness of the broadcast system often depend more on the automatic broadcast control system software. We have considered the following points in software development:

1. Stable and diverse broadcasting functions: Firstly, it ensures stability and reliability, and can provide various broadcasting forms such as sequence, insertion, timing, and delayed broadcasting, and can flexibly call hard disk output signals and external signals.

2. Flexible editing functions: insertion, deletion, modification, etc. of program linking lists.

3. Improve and facilitate the upload function: provide real-time and scheduled uploads of materials.

4. Friendly human-machine interface: in line with the operator's work habits, easy to learn and use, with a Chinese interface.

5. Strong software security: Set the user's security level to ensure the security of system data, and automatically lock various destructive violations during playback.

6. Software should consider being easy to upgrade or compatible with the development and updating of system hardware. The system adopts an open architecture, providing functions for device expansion and functional expansion. Capable of accepting third-party software and supporting mainstream international standard protocols.

7. Provide diagnostic procedures. Monitor the status of major components such as video servers and matrices, and report any issues as soon as possible.

After multiple investigations, we have selected Beijing Daheng Company to develop the control software for this system. The software is based on the widely popular operating system platform Windows NT in the video industry, inheriting the characteristics of Windows NT, which is easy to learn and use.

The control software is written in VC++language, abandoning the convention of directly using the ready-made PROFILE protocol for control in the past. It is developed directly from the bottom layer. In this way, once the software needs to set parameters such as stream, it can be directly set by the software interface without the need for peer operation on PROFILE. This greatly develops the potential functions of PROFILE and improves the security of playback control.

The software includes upload, serial encoding, and broadcast control, and the system adopts two control methods: network cable and RS422. The entire control system consists of 5 industrial computers and 1 switch. Five industrial control computers are numbered 1-5, with numbers 1 and 2 being the main backup broadcast machines, number 3 being a serial single editor machine, and numbers 4 and 5 being upload control machines. They are connected to two PVS1024 through a Switch to form a subnet and controlled by a network cable. The matrix, switching station, and uploading video player are controlled by RS422. The system control diagram is shown in Figure 2

When uploading materials, the system controls the upload player, matrix, and PROFILE. Based on the video signal source of the upload channel, the corresponding activated player and external signal source are selected to input the materials into the hard disk. The system can achieve timed uploading of external signals. After the materials are uploaded, they can be transmitted to each other through the fiber optic cable between the two hard disk machines as backups. The viewing channel on the upload end can also serve as a delayed broadcast channel for the system.

Serial editing is the process of editing materials and external signals present in the hard drive into a broadcast serial single. We designed it to be completed by a serial single editing machine, which is connected to the advertising department through a gateway and can complete the import of advertising broadcast serial single. After the completion of the integrated network for production and broadcasting on the entire station, it can be upgraded to the import of the entire broadcast serial single, reducing the workload of staff and errors.

The broadcast control of software is to broadcast materials under the control of a broadcast control machine in the order of the program edited by a serial single editing machine. We use a method where one broadcast control machine controls the broadcast of two channels simultaneously, and the other broadcast control machine is in a hot backup state. The system simultaneously controls PROFILE, matrix, and broadcast switching stations, which can achieve several broadcast methods such as start, timing, sequence, sequential insertion, and delayed broadcast. It can also adjust the broadcast schedule temporarily according to broadcast requirements, and control the switching stations to move subtitles and station logos up and down. The backup PROFILE is equipped with a looping broadcast channel for emergency program filling.

5、 System security

Two hard disk servers in the system mirror and backup each other, using a RAID-3 hard disk chassis. Each hard disk server uses a Duplisk card to carry two mirrored backup system disks. The server is connected to the RAID controller via fiber channel, and when the server starts, the RAID controller can be detected. The RAID controller is also divided into two main and backup disks, which can be hot swapped.

Both the main and backup broadcasters can independently complete the hard disk playback of two channels. If the main broadcaster fails, the system will automatically switch to the backup broadcaster for operation. And issue an alarm signal to notify technical personnel to come for repair. After troubleshooting, the anchor can be manually switched back to work. Considering that the matrix bears the dual task of uploading and broadcasting signal calls, we have specially equipped QUARTZ 24x16 as a backup matrix for security reasons. On the one hand, it provides backup signals for switching stations, and on the other hand, it can directly replace the main matrix for broadcasting.

Compared to the existing hard disk systems in China, our fully digital hard disk broadcasting system has many outstanding advantages:

1. In terms of hardware, we adopt GVG's latest model PVS1000 series products, RAID-3 hard disk chassis, and the latest technology included in the latest products provide us with better choices in software control.

2. The broadcasting software was designed by Dahengyin Video Company of the Chinese Academy of Sciences. It is the earliest manufacturer in China to enter the development of GVG hard drives, with strong technological strength and rich experience accumulation. The company has settled in our station for development, and the specific requirements of our station are very clear. Therefore, the control software has almost pushed the function of GVG hard drive broadcasting to the extreme.

3. Taking the lead in moving towards digitalization, this broadcasting control system currently uses digital signal transmission internally, with only one line for video and audio transmission, greatly simplifying the wiring. Especially important, the system provides a guarantee for the future construction of an integrated network for broadcasting and editing across the entire station.

The system has been running for more than half a year now, working stably and reliably. The system's technical indicators have met the relevant standards of the State Administration of Radio, Film and Television, and the quality of program broadcasting has significantly improved. At the same time, due to the use of pre upload, the system completely eliminates incidents of poor or missed broadcasts caused by video recorders and videotapes, achieving good social benefits.

Excerpt from: hc360 Huicong Network Radio and Television Industry Channel