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Implement broadcast video infrastructure

Posted: 16 Aug 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Tam Do? Altera? FPGA? spotlight? communications?

plds will play an increasingly important role in the digital buildup of the broadcast industry infrastructure. The key value proposition of PLDs is that they give equipment manufacturers the flexibility and upgradeability that this industry requires to remain competitive.

The first stage of the video broadcast chain is the professional digital video camera that captures A/V content. The video can either be SD or HD. This digital camera will typically have a Society of Motion Picture and Television Engineers-defined serial data interface (SDI) output. SDI is an uncompressed video stream running at either 270Mbps (SD), 1.485Gbps (HD) or 2.97Gbps (1080p HD). Altera's Stratix II GX FPGA, with an integrated Serdes and clock/data recovery, processes the video stream onto the SDI output of the camera.

Limiting the available bandwidth in the digital domain with various video compressions will manifest in different ways when displaying the decoded stream. Pushing the video compressor hard will produce block noise or blocking artifacts, due to the discrete cosine transform (DCT) of the block-based codec. Video pre/post-processing makes it easier for the encoder to compress the video, enabling it to improve picture quality and reduce delivery bandwidth requirements. This capability is critical for cable, satellite, telcos and IPTV broadcast business models, where meeting high-quality demands must be achieved within narrow bandwidth constraints. Some of the preprocessing may involve using 2D filtering to smooth out some of the high-frequency content before it enters the encoder to reduce the amount of block noise.

Video compression
The next stage sets the course for compressing the pre-processed raw video data before transmitting to the end-user. There are various generations of compression standards, ranging from MPEG-1 to MPEG-4, with four methods for compression: DCT, vector quantization, fractal compression and discrete wavelet transform.

MPEG-2 is the dominant standard for DTV across the world, with digital cable, satellite and terrestrial broadcasters still using this standard. As the broadcast industry leans toward more HD content, the given transmission bandwidth is under ever more pressure to make it fit into the predefined analog bandwidth spectrum. As IPTV starts to roll out on the traditional telco wiring systems, MPEG-2 will not be economical or feasible for carrying video programs to consumers. The ITU-T Video Coding Experts Group, together with the ISO/IEC MPEG, introduced the MPEG-4-Part 10 (also called H.264) standard. Capable of providing good video quality at bit rates substantially lower than previous standards, H.264 does so without being much more complex as to make the design impractical to implement. An additional goal was to allow the standard to be flexible enough to be applied to many applications (both low and high bit rates, and low- and high-resolution video) and to work well on a wide variety of networks and systems.

There are also other compression standards, such as JPEG2000, which use state techniques based on wavelet technology. The architecture should lend itself to portable digital cameras, video storage and advanced medical imaging.

Video distribution
The compressed video can be routed and distributed within the broadcast studio facility by using the ASI standard for short-distance routing. The industry trend is to use a video-over-IP network to distribute video data over long distances. Altera offers a video-over-IP reference design that demonstrates the transmission of MPEG-2 transport stream data over IP-based networks. The reference design bridges one or more compressed video streams and IP packets with 100MbE or 1GbE. The ASI encode and decode reference design is also available. A DVB-ASI is a serial data transmission protocol that transports MPEG-2 packets over copper-based cables or optical networks.

Production studio and head-end equipment can usually perform video scaling and de-interlacing for applications such as SD to HD conversion or vice versa. Other applications include filters for edge-detection processing, vertical motion filter and inter-field motion filter.

One of the common requirements for many professional studios is the ability to use single- or multiple-display devices to show a variety of normal SDTV or HDTV signals. Easy control of the switching between various sources via a remote control is important in creating a professional, easy-to-use system. Thus, video scaling and de-interlacing are essential for the video switcher/router capable of handling different types of video resolution for video switching, routing and local displays.

Color-space conversion
Since there are many video formats that broadcasters have to work with, the broadcast studio must be able to convert between different color spaces and video formats. Color is described using different color space domains, with each space domain associated with various applications based on system requirements. Color information is determined by two separate chrominance signals, Cb and Cr, which are a function of a third signal, Y, the brightness or luminance signal. The RGB color space is also defined by three components, red, green and blue. Color space conversion is often necessary when transferring data between devices that use different color space models.

The overall digital broadcast infrastructure originates with the video content creation from either the TV studio or the motion picture production studio. The creation process interface will use SDI for transporting raw video to a storage device or to some type of nonlinear editor for video editing and feature enhancement. The final edited video is compressed using MPEG-2, JPEG2000 or H.264 during the encoding process before being distributed to the consumers via cable, satellite, terrestrial or the latest IPTV technology network.

- Tam Do
Sr. Technical Marketing Manager
Broadcast/Consumer Applications Business Unit, Altera

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