Introduction to Video Compression - A Practical Guide to Video and Audio Compression - page 11

Table 1-1 Units of Measure

Quantity Unit of measure Abbreviation

Data transfer Bits per second bps

Thousands of bits per second (Kilo) Kbps

Millions of bits per second (Mega) Mbps

Thousands of millions of bits per second (Giga) Gbps

Data storage Bytes B

Thousands of bytes (Kilo) KB

Millions of bytes (Mega) MB

Thousands of millions of bytes (Giga) GB

Millions of millions of bytes (Tera) TB

Thousands of Terabytes (Peta) PB

Audio levels Tenths of Bels (deci) dB

Frames Frames per second fps

Tape transport Inches per second ips

Screen resolution Dots per inch dpi

Film resolution Dots per mm dpmm

twice the frame rate, while for progressive displays, they are the same. For example, 525i60
and 625i50 describe the American and European display formats, respectively.
It is very easy to confuse bits and bytes when talking about video coding. Table 1-1
summarizes the basic quantities we will be using.
In the abbreviations we use, note that uppercase B refers to bytes, and lowercase b is
bits. So GB is gigabytes (not gazillions of bytes). When we multiply bits or bytes by each
increment, the value 1000 is actually replaced by the nearest equivalent base-2 number. So
we multiply memory size by 1024 instead of 1000 to get kilobytes. As you learn the num-
bers represented by powers of 2, you will start to see patterns appearing in computer sci-
ence, and it will help you guess at the correct value to choose when setting parameters.
Already this is becoming complex, and we have scarcely begun, but don't worry, we
will get to the bottom of it all in due course. Everything will become clear as we persevere
and work our way steadily through the various topics chapter by chapter.

1.31 What Did You Call That Codec?

Video compression terminology is already confusing enough without having to worry
about codecs having several names for the same thing. There are lots of unfamiliar
terms and concepts to understand. It makes it even more difficult for the beginner
when new codecs are launched with several names. The latest codecs are described
elsewhere in the topic, but one in particular leads to much confusion even amongst
experienced professionals. The MPEG-4 part 10, otherwise known as H.264 codec, is part
of a family of video encoders that is listed in Table 1-2.