Bit Rates

Bit Rates

All video formats have a specific bit rate, which is also often described as data rate. You can think of the bit rate as the "speed" of that particular format. The bit rate refers to how many bits are transferred or processed in a given period of time.

When working with video stored on hard drives, we can think of the bit rate as the speed with which a given format is read from, or written to a hard drive. Video storage needs to have data rates that exceed the specific rate of the video format in order to be able to reliably handle that format without problems. An example of a specific bit rate would be the DV format, which has a bit rate of 25 Megabits per second. (we'll re-visit specific bit rates and media hard drive storage in the section Media Storage for Post Production).

Bits and Bytes

One area of confusion for many people is that we often seem to use an apples to oranges type of comparison with bit rates, as video formats and storage tend to be quoted using two different measurement methods.

• Video formats' bit rates are usually listed in Megabits per second.
• Hard drives (storage for video) usually list bit rates in Megabytes per second.

Although the terms look similar, they are quite different.

Bit: A binary digit, either a 1 or 0.
Byte: 8 bits of data.

Megabit: 1 million bits. Usually abbreviated as Mb.
Megabyte: 1 million bytes. Usually abbreviated as MB.

When working with video, bit rates are generally calculated in Megabits or Megabytes per second. In addition, we may also see several different ways of expressing the bit rate:

• Megabit per second: Mbps, Mb/sec, Mbit/sec
• Megabyte per second: MBps, MB/sec, MByte/sec

*We'll list Megabits per second as Mbit/sec and Megabytes per second as MByte/sec to try and limit the confusion of what is being discussed.