MSc ICT Student ID 56579RENNIE RAMLOCHAN

THE UNIVERSITY OF TRINIDAD ANDTOBAGO

Multimedia Technologies

Assignment 1

The Virtual Museum Project Video is being streaming over the Internet Video streaming over theInternet is difficult because the Internet only offers best effort service That is it provides noguarantees on bandwidth delay jitter or loss rate Specifically these characteristics are unknownand dynamic The bandwidth available between two points in the Internet is generally unknownand time-varying If the sender transmits faster than the available bandwidth then congestionoccurs packets are lost and there is a severe drop in video quality If the sender transmits slowerthan the available bandwidth then the receiver produces sub-optimal video quality The goal toovercome the bandwidth problem is to estimate the available bandwidth and than match thetransmitted video bit rate to the available bandwidth To avoid the undesirable symptoms ofcongestion control procedures called rate control or congestion control are often employed tolimit the amount of network loadThe end-to-end delay that a packet experiences may fluctuate from packet to packet Thisvariation in end-to-end delay is referred to as the Delay jitter Delay jitter is a problem becausethe receiver must receivedecodedisplay frames at a constant rate and any late frames resultingfrom the delay jitter can produce problems in the reconstructed video eg jerks in the videoThis problem is typically addressed by including a play out buffer at the receiver A play outbuffer Caching allows nodes to quickly fetch the required documents without incurring annoyingdelays by circumventing the need to contact the original host While the play out buffer cancompensate for the delay jitter it also introduces additional delayThe third fundamental problem is losses A number of different types of losses may occurdepending on the particular network under consideration For example wired packet networkssuch as the Internet are afflicted by packet loss where an entire packet is erased (lost) On theother hand wireless channels are typically afflicted by bit errors or burst errors Losses can havea very destructive effect on the reconstructed video quality To combat the effect of losses a videostreaming system is designed with error control classes such as (1) forward error correction (2)retransmissions (3) error concealment and (4) error-resilient video codingThe goal of error-resilient video coding is to design the video compression algorithm and thecompressed bit stream so that it is resilient to specific types of errors Scalable coding essentiallyprioritizes the video data and this prioritization effectively supports intelligent discarding of thedata For example the enhancement data can be lost or discarded while still maintaining usablevideo quality The different priorities of video data can be exploited to enable reliable videodelivery by the use of unequal error protection (UEP) prioritized transmission etc

Video Window Size The digital video stores a lot of information about each pixel in eachimageframe It takes time to display those pixels on your computer screen If the window size issmall then the time taken to draw the pixels is less If the window size is large there may not beenough time to display the image or single frame before its time to start the next one and any lateframes may result in delay jitter that can produce problems in the reconstructed video eg jerksin the video 3Ways to solve this problem (1) Choose an appropriate window size The reductionof the window size to anything less than the size or resolution of the original video source willinvolve some sort of compression This is because the same information is being represented butin less space Note Reducing the window size may not always therefore produce desirableresults and will depend upon the content of the video(2)Make Use of Fast hard discs to enablingeach frame to be read from the disc faster (3)Make Use of hardware accelerated playback eggraphic cards now include facilities for acceleration and video playback

Frame Rates The issues here are similar to those above - too many pixels and not enough time tomove the data from hard disc or CD to screen One way to overcome this is to compress the dataso that less data is transferred from disc to screen At smaller window sizes eg 160 x 120 pixelsvideo played at reduced frame rates is acceptable At larger window sizes the video cansometimes appear jerky

Image Quality The image quality will depend on the quality of the original source and thedegree of compression used A lower setting will result in greater compression and smaller filesizes but the quality of the resulting video sequence will be reduced

References

http wwwencyclopediajrankorghttp wwwietforgrfchttpwwwiitbasbghttpwwwhplhpcomtechreports2002HPL-2002-260pdf