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Video Encoding: Go for the Specialist or the Jack-of-All-Trades?

October 5, 2012 | Telepresence Options
Video_ARM_DSP.jpg
This is a general layout of a video ARM DSP. The ARM core runs the embedded operating system, working like a traffic cop to control input and output.

When it comes to video encoding, the choice between hardware and software comes down to flexibility, latency, and cost.
By Scott Grizzle

One of the hardest choices encoding technicians have to make is deciding between hardware and software. Hardware-based encoders and transcoders have had a performance advantage over software since computers were invented. That's because dedicated, limited-purpose processors are designed to run a specific algorithm, while the general-purpose processor that runs encoding software is designed to handle several functions. It's the specialist versus the jack-of-all-trades.

In the past few years, processors and workflows have changed. The great disruptor has been time and the economics of Moore's Law, which famously says that the number of transistors incorporated in a chip will approximately double every 24 months. The logical outcome of Moore's law is that the CPUs get more powerful by a factor of two every few years, but more recently processing power seems to double every few months. Lately, Intel -- whose co-founder Gordon Moore coined Moore's Law -- has been adding specialty functions along with its math co-processors to equalize the differences between general-use processors and specialty processors.

There are many layers and elements to both a general-purpose processor and a task-specific hardware processor. The general-purpose CPU is the most common -- there are literally billions of them in all manner of computing devices -- while the more purpose-oriented processors include digital signal processors (DSPs), field-programmable gate arrays (FPGAs), and integrated circuits (ICs) that are available for various industrial appliances and widely used in cellphones. Many of the structures and elements are similar across all types, but there are considerable differences. If you are not familiar with the elements of the various types, here are the basic structures of both.

The General-Purpose CPU

The general-purpose CPU is laid out with flexible core elements as the arithmetic logic unit (ALU), control unit (CU), and accessory elements that offer extra features for performance. Basically these two cores talk to each other, bring in memory as needed, and send work to the other elements. Other elements include I/O processors, logic gates, integrated circuits, and -- on most newer processors and especially on the Intel Xeon processors -- a beefy math co-processor. The math co-processor assists the ALU and can handle the more extreme and complex mathematical computations. Essentially, it gives the processor the extra horsepower it might require.

The Dedicated Processor

Specific-purpose hardware encoders have been around longer than general-purpose processors, and the latter have been slower at mathematical equations or algorithm problems. History is vitally important to understand the market and technology, not to mention get a sense of what the future holds. The earliest example of encoding was in 1965, when the Intelsat 1 (Early Bird) became the first commercial deployment of a satellite to downlink video and audio. Since then, the world has been using specific processors to process video, and the technology has made leaps and bounds to offer higher density and quality.


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