Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

1, MPEG-4 design and implementation of MPEG-4 encoding card

Structure of encoded cards is shown in Figure 1, including audio and video A / D, and the required compression chip VW2010 SDRAM, and the clock power supply modules.

As input and output of VW2010 audio and video are digital formats, including video input and output is ITU-R BT. 656 format, the audio input and output is the I2S format. Hence the need for audio and video analog input signal to do analog-digital conversion and format 12S audio data, ITU-R BT. 656 format video data, as VW2010 input data to encode. Therefore also need to choose some of the peripheral chips and VW2010 to coordinate with, to complete the coding process.

Coded card system block diagram shown in Figure 1, PCB shown in Figure 2. as the core of the system, VW2010 is connected to host machine by the PCI bus, mainly sent receiving VW2010 initial configuration data and real-time control information sent from host machine, while VW2010 compressed MPEG-4 video streams, audio streams connected to the host by PCI bus. VW2010 go through the I2C bus to control all audio and video A / D, to initialize for its internal configuration registers.

Analog audio and video signal go through the audio and video A / D to sample encode, the sound signal become to be I2S format to get into VW2010, the video signal become into 8-bit parallel ITU-R BT. 656 format data get into the VW2010, VW2010 program the coded format and work way sent from the host according to synchronization and compression audio/video and get MPEG-4 data to send to the host. In addition to MPEG-4 encoding chips VW2010, the design must also select the video A / D chip, audio A / D chip, SDRAM memory chips, power chips, resistors, capacitors and other discrete components.

Video A / D chip: use the Philips SAA7115, the chip has 6 analog video signal input (such as 6-channel 2-way composite video or S-video and two composite video, one S-Video 4 composite video inputs), two 9-bit ADC, the input video signal selection can achieve by I2C bus to set the internal register. A variety of PAL signals and NTSC, SECAM signal can be automatically identified and decoded the analog-digital conversion ITU-RBT. 60l, ITU-R BT. 656 format video data. To composite video signal brightness and chromaticity do a better separation ,chip has adaptive comb filter, decoded video VBI data. It is a relatively high-end video A / D chip.

Audio A / D chip: Audio A / D chip select Philips UDAl342TS, the chip has a 4-channel analog to digital converter (ADC) and 2-channel digital to analog converter (DAC). Has characteristics of low voltage and low power consumption, supports 24-bit I2S data format, can be controlled through the I2C bus. Although the chip has both A / D and D / A functions, but when the A / D and D / A the same time working, the audio sampling rate must be the same, for this reason, only the design of its A / D: function, The D / A is selected CS4331-KS. The chip is a complete stereo analog-input audio data in I2S format, left and right stereo output with 96dB of dynamic range, 24-bit conversion, 5V power supply, small package, only 8 pins.

Memory chip: when VW2010 codec , need to access for video data access, so the needs memory of 4 ~ 8MB. The design uses MT48LC2M3282 chip.     Power chip: This system requires use 3.3V and 1.8V, 5V power supply in PCI bus need to be converted. Taking into account all the chip power consumption and power efficiency, power dissipation and so on issues, also using switching power supply as the power chip LM2596.

2, MPEG-4 Design and implementation of MPEG-4 decode

Decoding is the reverse process of encoding, decompression card block diagram shown in Figure 3, PCB shown in Figure 4. VW2010 is the core processing chip of decompression card, processed MPEG stream data go by the integrated PCI interface chip input. In addition to complete MPEG decompression addition, VW2010 chip ADC also provides audio control (through the I2C bus). VW2010 MPEG stream data to the decompression processing to generate a standard ITU-656 digital video signal and a standard I2S digital audio signals; produced by ITU-656 digital video signal directly to the real-time monitoring subsystem image segmentation; generated I2S DAC digital audio signal through the audio circuit to produce analog audio signals, analog audio signal through the output processed audio directly to the real-time monitoring subsystem selector module to select the output.

The codec card has a very flexible choice for using in the actual systematic construction , because embedded PCI interface structure can be combined with  communication platform, PC platform, the IPC and other platforms. Both can be stored locally, but also for network transmission. The separation design of codec card design can effectively reduce costs, both encode and finish uploading network then connect decoders in the end of network far-end, and then restore the analog signal to directly access the monitor display, so that the monitoring center can connected with monitor , TV wall of previous module system, no necessary for a PC , to achieve a seamless upgrade requirements, and can directly access to PC and soft decode MPEG-4. In practice, achieved good results, the need to improve applications and development of the upper image management software.