The expansion of digital video technology from a few dedicated applications, such as camcorders and security systems, to a wider range of consumer products strains traditional video development methods. Historically, these methods include considerable amounts of hand-coding by experts who are familiar with the latest coding/decoding (codec) standards and can write assembly code for high-performance signal processing platforms.
Manufacturers of signal processing technology are addressing this problem by providing development environments that integrate processors, development tools, software and systems expertise to enable designers to work at a high system level of abstraction in developing video applications. This allows designers to focus on the application functionality and implement video, audio, voice and imaging technology through simple calls to an application programming interface (API) that handles details such as the implementation of specific codec engines and matching screen resolution.
A new generation of video applications
As the cost of implementing digital video has continued to drop, more embedded developers are incorporating video and audio technology into a wide range of products. For example, Figure 1 illustrates how set-top boxes (STBs) are integrating home surveillance security systems to enable homeowners to view visitors on their TV screens. At the same time the quality bar is rising for both traditional and nontraditional video applications. Improved computational algorithms are being developed to intelligently adjust contrast and focus. Flexible processing options will enable users to capture images using a variety of settings, including black/white, color, infrared, heat and sensor. Intelligent cameras are being developed to only capture the image when everyone in the frame has their eyes open.
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Figure 1: Example of how a set-top box can be integrated with home surveillance security systems to identify a visitor at the front door and post a notification on the television.
Traditional codec implementation methods
The increasing use of video and increasing sophistication of new video applications is focusing attention on the limitations of traditional video development methods. One of the greatest obstacles is the need for hand coding of codec algorithms that compress a digital stream for transmission or storage and decompress it for viewing and editing. Today's codec standards are very complex and they are continually being improved to enhance video quality and reduce bandwidth consumption.
Consequently, many man-months are typically required for engineers to implement them in embedded video applications. Generally codecs are initially developed in a higher-level language such as C/C++ and later parts of the code are rewritten in assembly to optimize their performance and power consumption based on the hardware implementation. This second stage of the programming effort requires considerable expertise in the specific hardware platform.
While earlier generation codecs such as MPEG2 have stabilized, newer higher-efficiency codecs such as MPEG4 and H.264 are still undergoing refinements so consideration must be given to the potential for changes during the development process and in future upgrades. Newer codecs also have larger toolsets that provide developers with more options in characterizing the video stream. For example, one codec stream may allow the use of interlaced profiles while another does not.
Hardware considerations
The codec usually runs on either an application specific integrated circuit (ASIC) or a digital signal processor (DSP). An ASIC is custom design for the application so it typically offers lower power consumption and a smaller footprint. The disadvantage of using an ASIC is that the nonrecurring engineering expenses are high and implementing changes, such as to accommodate evolving codec standards, can be expensive. The implementation of a new codec usually requires increasing the die size of the ASIC device.
The DSP provides full software programmability including field reprogramming capabilities, which enables a user to roll out an MPEG 2 product and later upgrade to H.264 video codec. The DSP also makes it easy to deliver a product that supports multiple codecs and enables updating of codecs in the field in response to changes in the standards. Additionally, the DSP may be incorporated into a system on chip (SoC) that provides the opportunity to reduce part count by combining it with additional functionality, such as a general purpose processor (GPP) and accelerators.
What about the application?
Digital video implementation is only one part of most of today's innovative applications. The application, which typically runs on a GPP, provides the user interface and specific features that differentiate the product from others in its category. One of the critical roles of the application is bringing the hardware and the software together, such as buffering video between the codec and the video ports. Additionally, the application requires an operating system, such as Linux or Windows CE, which must also handle Ethernet stacks, wireless stacks, input/output device drivers, etc.
Next: Hardware abstraction through software
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