Chapter 14

On Todays lesson 

Objectives

• Define data rate
• To calculate the file size of an uncompressed digital video
• To calculate the file size of an uncompressed audio file
• To determine the factors of graphics selection in a multimedia project 

What is a Data Rate?

A data rate is the rate at which information being transferred.

It is expressed in terms of [amount of information] per [unit of time].

Eg. Data rate used to describe the speed of a hard drive is Megabytes/second.

For compressed audio files, kilobits/second is used.

When a data rate is determined, you can calculate the estimate amount of hard drive space needed to store the video. 

 

Calculating the File Size of an Uncompressed Audio File

The formula is as follows:

8-bit mono

16-bit mono

8-bit stereo

16-bit stereo

Seconds x kHz = Size

(Seconds x kHz) x 2 = Size

(Seconds x kHz) x 2 = Size

([Seconds x kHz] x 2) x 2 = Size

([Seconds x kHz] x2) x 6 = Size

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16-bit 5.1

Eg. The file size for a 30 seconds of 16-bit, 11kHz mono audio is: (30 X 11) X 2 = 660KB

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Exercise : Let’s calculate the total file size of one minute of 24-bit full screen (VGA) video at 30fps together with its uncompressed stereo 16-bit 44.1kHz PCM audio 

 

Answers:

Total uncompressed video data size:

= 640 X 480 X 30 X 3 X 60

= 1,658,880,000 bytes

Total uncompressed audio data size:

= 60 X 44.1 X 2 X 2 = 10584KB X 1024 = 10,838,016 bytes

Total file size:

= Total video data size + Total audio data size = 1,658,880,000 bytes + 10,838,016 bytes = 1,669,718,016 / 1,073,741,824
= ~1.55GB 

 

Factors to consider when selecting graphics to be used in a

multimedia project:

Purpose:

– Avoid using images for “filler” or when they have little in common with the overall message or purpose.

– A common mistake is to trivialize products with cartoons that can be distracting to the viewer.

– If multiple images are used, make sure they reflect a common message such as providing the user with an example or an illustration. 

 

Factors to consider when selecting graphics to be used in a

multimedia project:

b) Quality:

– Any image used in a multimedia product should reflect the overall quality desired of the entire product.

– The image colour depth has to be considered, especially for applications that will be displayed on systems using a lower colour capability. 

 

Factors to consider when selecting graphics to be used in a

multimedia project:

c) Cost:

– The cost of a graphic is directly related to its purpose and quality.
– Copyright and ownership of graphics will determine who is to be paid. 

 

 

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