How to Add Low-Power, Multi-Codec, Digital Video and Audio to Your Next ASIC or SOC Design

How to Add Low-Power, Multi-Codec, Digital Video and Audio to Your Next ASIC or SOC Design

Since the early 1990s, video compression has grown increasingly important for the design of modern electronic products because it aids in the quest to deliver high-quality video using limited transmission bandwidth and storage capacity. Many consumer products now incorporate video-recording and video-playback functions. ASIC, SOC and ASSP design teams developing chips for such products need ways to quickly add proven, tested audio/video functions to their designs. It is now possible to obtain tested, off-the-shelf IP blocks and firmware that implement multiple digital-video and audio codecs. These products allow ASIC and SOC design teams to literally drop digital audio and video into their design without the need for detailed knowledge of the new video standards.

Video Basics

The first widely successful video-compression standard was MPEG-2. It is used in DVD players, its first big success, and then grew into other applications such as satellite and set-top boxes. The MPEG-4 and H.264/AVC video-compression standards then followed some years later. With all video-compression standards, the goal is to deliver high-quality video with minimum bandwidth. As compression technology advances, codec (coder-decoder) developers can exploit increasing processor performance to achieve higher compression ratios while delivering images with much higher visual quality.

Digital video encoding starts with a series of still images (frames) captured at a certain frame rate (usually 15, 25, or 30 frames/sec) by cameras use CCD or CMOS sensors to capture the images. These sensors capture red, green, and blue (RGB) light but the RGB images they produce do not directly correspond to the way the human eye works. The human eye uses rods and cones to separately sense light intensity (luma) and color (chroma). The eye is more sensitive to luma than chroma because it contains more rods than cones. Consequently, most video-compression systems start by transforming RGB pictures into luma and chroma (YUV) images. To save bits in the video stream, compression schemes subsample the image's chroma portion. Thus most digital video compression schemes transform a series of YUV images into a compressed video stream while video decompression streams expand a compressed video stream into a series of still images coded in YUV format.

Digital video compression schemes use many of the lossy compression techniques originally developed to compress still images. Lossy compression techniques identify and discard portions of an image that cannot be perceived by the human eye. Digital video compression benefits even more from lossy compression schemes because any image imperfections produced by compression appear fleetingly in the video stream and are therefore even less perceptible.