Frames
Video is a stream of images.
Digital video is more efficient because it identifies portions of the frame that change instead of recreating the full image.
Frame rate - the frequency at which an imaging device displays consecutive images.
Humans can process 10 to 12 separate images per second individually.
24, 25, and 30 frames per second are standard.
Frame interlacing
Flicker is visible fading between cycles.
Flicker occurs on CRTs when driven at a low refresh rate.
There is not enough bandwidth to send frames at 24/30 frames per second on broadcast networks.
Interlaced video doubles the perceived frame rate without consuming extra bandwidth.
The interlaced signal contains two fields of a video frame captured simultaneously.
A Phase-Alternating Line (PAL)- -based TV display scans 50 fields every second: 25 odd and 25 even. The two sets of 25 work together to create a full frame every 1/25 of a second.
Allows more detailed images to be created.
Image softening occurs during fast motion sequences or strobing artifacts on patterns.
Progressive Video
Progressive Video is made up of consecutively display frames that contain all of the horizontal lines.
Images appear smoother, fast-motion sequences are sharper and with less artefacts.
Primary drawback was the higher bandwidth requirement.
Formats and Resolutions
Common analog aspect ratio - 4:3 or 1.33:1
Common digital aspect ratio - 16:9 or 1.78:1
Color Standards
Dictate number of visible lines and vertical blank interval (VBI)
VBI used fro closed caption, teletext, timecodes
Color broadcast created by 3 monochome images, red, green, and blue. when dispalyed in rapid succession image blend together to produce full color image
Quantization applied to voice
The process of conversion of analog voice into digital voice is quantization.
1 byte represents 0-255 values. Voice is limited to +127 to -127
Human audible 20-20,000 Hz
Human speech 200-9000 Hz
Telephone range 300 - 3400 Hz
Nyquist theorem 300 - 4000 Hz, sample at twice highest frequency - 8000 times per second (2 * 4000)
- Sampling - DSP periodically samples the analog signal, output is pulse amplitude modulation (PAM) measured in volts
- Quantisation - DSP matches PAM signal to a segmented scale that measures the amplitude
- Compression - DSP compresses voice samples to reduce bandwidth requirements.
Each sample is 8 bits,
- One polarity bit: indicates positive or negative signals
- Three segment bits: identifiy the logarithmically sized segment number (0-7)
- Four step bits: identify the liner step within a segment
Required bandwidth is 64 kbps, 8000 samples per second at 8 bits each.
Cisco Digital Media Suite (DMS)
- Cisco Digital Signs - interactive premise based digital signage
- Cisco Cast - provides IPTV and controls live and recorded video to displays
- Cisco Shows and Share - social video to capture, edit, and receive live and recored content on endpoints
- Cisco Digital Media Manager - central web-based management application
- Cisco Digital Media Player (DMP) drives displays
Cisco Digital Media Encoder 1000 and 2000 - single and multichannel audio and video encoding
Cisco MXE Media Experience Engine (3500 built on Cisco UCS)
Made with Bullet