Digital audio/video decoder
The use of digital, as opposed to analog signals, for television broadcasts and the transmission of other types of video and audio signals has been proposed as a way of allowing improved picture quality and more efficient use of spectral bandwidth over that currently possible using analog NTSC television signals. Digital video representation of AV material facilitates its usage with computer controlled electronics and also facilitates high quality image and sound reproduction. Digital AV material is typically compressed (encoded) in order to reduce the computer resources required to store and transmit the digital data. A digital image video recording creates an enormous amount of digital data. To accommodate digital image video device bandwidth limitations, and deliver digital data at increased transmission speeds, digital image data is compressed, or encoded, before being transmitted or stored. A compressed digital video image is decompressed, or decoded, prior to its display. Examples of widely used compression techniques (standards-based) are those that comply with the Moving Pictures Experts Group (MPEG) and Joint Pictures Experts Group (JPEG) standards. Generally, a digital TV receiver receives and decodes a video signal compressed in the MPEG2 format at a decoder to display the video on a screen. Compressed audio and video information transmitted in an MPEG transmission stream to an MPEG decoder is temporarily stored in a memory of the decoder until it is needed to reproduce original sounds and images. Digital video decoders such as found in digital television receivers or in set-top boxes (STB), require accurate synchronization between the encoding rate of the incoming video signals and the decoding rate of such signal. Generally, synchronization in such video decoders occurs in a two-stage process. In the first stage, a digital video decoder analyzes the incoming video bit stream transmitted by the encoder to determine the clock frequency, or base clock, of the encoder. In the second stage of synchronization, the decoder uses the recovered base clock rate of the encoder to reproduce video frames at exactly the same rate as that of the transmitter's encoder. The ability to process audio information has become increasingly important in the personal computer (PC) environment. One of the key components in many digital audio information processing systems is the decoder. Generally, the decoder receives data in a compressed form and converts that data into a decompressed digital form. The decompressed digital data is then passed on for further processing, such as filtering, expansion or mixing, conversion into analog form, and eventually conversion into audible tones.
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