Digital Video and Multimedia To produce videos that are worthy of inclusion in a web-based multimedia application you need to understand: How video is

Digital Video and Multimedia

To produce videos that are worthy of inclusion in a web-based multimedia application you need to understand:

How video is captured?How video is stored?How video is transferred?How video is displayed?How to shoot a good video?


How video is transferred?

The output of the CCD (sensor) is converted by the camera (and compressed) into a signal that is tranfered to and displayed by monitors and TVs. The signal must contain:

• Luminance information (brightness)• Color information• Synchronisation information (to keep the luminance and color together)

The better this information is separated in the signal the better quality the output. If all the components of the signal are combined there can be interference between the components as the signal passes through a piece of equipment (a DVD player for instance)

The signal must also include the audio.



Several standards govern the transfer. In order from lowest to highest quality they are Composite, S-Video, Component and HDMI/DVI.

HDMI and DVI transfer the signal in digital format. The others transfer the signal in analog format.



Composite

All information is combined and carried in the one wire. Before our TV signal became digital, the analog signal coming in through a TV aerial was composite.

The problem with composite is that once the components of a video signal have been combined it is not possible to separate them again accurately. So a composite video signal gives a poor quality image.

Note that the sound is carried separately (red and white cables)



S-Video

Designed to stop the interference that can occur with a composite video signal. An S-Video cable is like the co-axial cable used with TV aerials. The color information is kept separate from the luminance and sync signal.

Note that the sound is carried separately.

S-Video plug Co-axial cable



Component

The components of the video signal are separated even more than in S-video so that there is even less chance of interference. The color information is separated into red and blue signals. Green is not required. If the amount of red and blue unknown, the remainder of the luminance signal must be green.

Note that the sound is carried separately.



HDMI/DVI

HDMI and DVI cables both carry digital information. HDMI also carries sound. Both these cables provide the highest quality digital video currently available.

http://cnettv.cnet.com/ask-anything-what-hdmi/9742-1_53-28819.html


How video is displayed

Digital video can be displayed using interlaced or progressive scanning.

Interlaced Scan

Half the picture appears on the screen at a time. The next frame (1/60th of a second later) displays the other half of the picture. When we say half of the picture we don’t mean top or bottom half for instance. The two halves interlace to give the complete image.



Digital video can be displayed using interlaced or progressive scanning.

Progressive Scan

The whole picture appears on the screen at a time.



With digital TVs and computer monitors the refresh rate is also important. Refresh rate refers to how often the screen is totally refreshed each second and is measured in hertz. Common refresh rates are 50, 100 and 200Hz.

With a higher refresh rate fast motion on a screen is smoother.

How is the situation handle where video is captures at 25fps and is shown at a refresh rate of 50Hz?



Analyse the features of this digital TV


How to shoot a good video

Types of shots

Extreme long shot (establishing shot) – let the viewer know where the action is to take placeLong shot – full body, establishing the main character(s)Medium shot – waist upClose-up – face (for interviews, etc.)

A good ration is 50% close-ups, 25% medium and 25% wide angle (long)

Angles of shots

Birds-eye – for establishing shotHigh angle – makes people look less scary and impressiveEye level – normal camera positionLow angle – makes people look more scary and powerful



Camera movement

This should be minimised for video that is going on the web.

To avoid camera movement:

•Use a tripod•Avoid quick zooming and panning•Plan a sequence of shots



Planning a sequence of shots

Example from http://multimedia.journalism.berkeley.edu/tutorials/shooting_tips/sequences/


Putting video on a web page

To put a movie from iMovie on to a web page you firstly need to save the movie in a compressed format.

Go to Share > QuickTime then Compress for Web

Open the relevant web page in Dreamweaver. Place the cursor where you need the movie to be inserted.

Insert > Media > Plugin

Select your movie and away you go.

Documents

Digital Video and Multimedia To produce videos that are worthy of inclusion in a web-based multimedia application you need to understand: How video is