VIDEO

Video: an electronic medium for the recording and display of moving visual media

Frame rate: The frequency with which the images or frames are recorded

Interlaced encoding

• The data from a single frame are encoded as two separate fields - the image is rendered by alternating between the even field and the odd field
• One contains the data for the even numbered rows and the other has the data for the odd-numbered row
• Originally used in TV broadcasting and adapted for video recordings

Spatial order: shows which should be the odd or even field

Temporal order: field or frame and which field represents an earlier moment of the time

• Field rate = 2 * frame rate
• Halves the transmission bandwidth requirements

Progressive encoding

• Stores the data for an entire frame and displays all the frame data at the same time
• Field rate = Frame rate
• Used by traditional film or video digitized from a computer displays progressive encoding

Pros of each encoding (relative to one another, i.e. pros of i = cons of p)

Interlaced encoding

• Lower bandwidth required (half to be precise), thus it's cheaper
• Refreshes faster
• Lower quality of images (blurred)

Progressive encoding

• Detailed frames with higher quality images

Purpose: decreases file size

• Removes neighbouring frames which are similar - minimising redundancy
  
• Some change in image data is redundant
• How redundant the change in an image between frames  determines the amount of compression possible 

CODEC - coder-decoder

Hardware: ADC & DAC, interprets one signal and convert it to another - usually for sounds

Sofware: Takes in the original file and pack it up in a specific format that adheres to documented standards so it can be interpreted by other software that utilises same codec

Multimedia container format: A type of file format that contains different types of media streams like video and audio and defines how the video, audio and other data is stored within the container 

• E.g. AVI or MOV
• AVI may not support new codec features like streaming media because it's in an older format

Spatial (intraframe) redundancy (within a frame)

• A sequence of pixels in a single video frame have the same value
• Only applied to individual video frame 
• An intercoded frame that is divided into macroblocks
• Blocks are not directly encoded with raw pixel values
• Encoder finds a block similar to the one in the last frame
• This frame is the reference frame

Temporal (interframe) redundancy (between the frames)

• Pixels in two or more video frames have the same value in the same location is getting compressed. There is a duplication of data between frames