QUESTION 4 ITOTAL MARKS: 25] Q 4(a) Describe what is meant by spatial and tempor
ID: 3920748 • Letter: Q
Question
QUESTION 4 ITOTAL MARKS: 25] Q 4(a) Describe what is meant by spatial and temporal compression for videos and for each give a simple example of an encoding scheme. [8 Marks] 4 Marks] Q 4(b) Briefly describe the purpose of the DASH protocol in streaming videos. Q 4(c) Consider the following two FEC schemes for VolP. Scheme 1: Send a redundant encoded chunk after 10 packets. [13 Marks] Scheme 2: Send a second lower resolution audio stream in parallel to the original stream. Assume the low bit rate encoding transmission rate is 10% of the transmission rate of the nominal stream. i) How much additional bandwidth does each scheme require? (3 marks) ii) How much playback delay does each scheme introduce? (4 marks) ) Suppose the first of every 6 data packets is lost. Which scheme will have better audio quality? Be sure to give your reason. (3 marks) iv) Suppose the first of every three data packets is lost. Which scheme has better audio quality? (3 marks) [End of Question 41Explanation / Answer
Spatial (or intraframe) compression takes place on each individual frame of the video, compressing the pixel information as though it were a still image. Spatial compression is often called intraframe compression. Spatial compression is applied to a single frame of data, independent of any surrounding frames. It is done with Spectral Encoding
Temporal (or interframe) compression happens over a series of frames and takes advantage of areas of the image that remain unchanged from frame to frame, throwing out data for repeated pixels.Temporal compression is often called interframe compression. Temporal compression identifies the differences between frames and stores only those differences, so that frames are described based on their difference from the preceding frame. Unchanged areas are repeated from the previous frames.
Temporal compression relies on the placement of key frames interspersed throughout the frames sequence. The key frames are used as masters against which the following frames (called delta frames) are compared. It is recommended that a key frame be placed once every 3 to 10 seconds. Videos without a lot of motion, such as talking head clips, take the best advantage of temporal compression . Videos with pans and other motion are compressed less efficiently.