Processing

prediction

sound and vision

(MPEG) stands for Moving Picture Experts Group is a working group of experts that was formed by ISO and IEC to set standards for audio and video compression.

MPEG 1 was created in 1993 the first compression standard for video and audio. It was designed to let moving pictures and sound encoded together into bit rate up 1.5mbits so it can fit onto a compact disk (CD).

MPEG 2 was created in 1995. MPEG 2 is the standard compression for TV and DVD it’s also combination of “lossy video compression and lossy audio data compression”. MPEG 2 has a higher bit rates by supports a wide range and provides for” multichannel surround sound coding.”

“MPEG-2 is capable of compressing the bit rate of standard-definition 4:2:0 video down to about 3-15 Mbit/s. At the lower bit rates in this range, the impairments introduced by the MPEG-2 coding and decoding process become increasingly objectionable. For digital terrestrial television broadcasting of standard-definition video, a bit rate of around 6 Mbit/s is thought to be a good compromise between picture quality and transmission bandwidth efficiency.”

http://www.bbc.co.uk/rd/pubs/papers/paper_14/paper_14.shtml

“MPEG 3 is the designation for a group of audio and video coding standards agreed upon by the Moving Picture Experts Group (MPEG) designed to handle HDTV signals at 1080p in the range of 20 to 40 megabits per second. MPEG-3 was launched as an effort to address the need of an HDTV standard while work on MPEG-2 was underway, but it was soon discovered that MPEG-2, at high data rates, would accommodate HDTV “http://en.wikipedia.org/wiki/MPEG-3

Video Encoding Techniques

Predictive coding is widely used in video transmission, especially for low bit-rate coding. Typically only some fraction of an image changes from frame to frame allowing straightforward prediction from previous frames. Motion compensation is used as part of the predictive process. If an image sequence shows moving objects, then their motion within the scene can be measured, and the information used to predict the content of frames later in the sequence.

(source : http://www.dcs.warwick.ac.uk/research/mcg/bmmc/index.html)

Macroblock is an image compression component and technique based on discrete cosine transform used on still images and video frames. Macroblocks are usually composed of two or more blocks of pixels. In the JPEG standard macroblocks are called MCU blocks.

The size of a block depends on the codec and is usually a multiple of 4. In MPEG2 and other early codecs the size is fixed at blocks of 8×8 pixels. In more modern codecs such as h.263 and h.264 the overarching macroblock size is fixed at 16×16 pixels, but this is broken down into smaller blocks or partitions which are either 4, 8, 12 or 16 pixels by 4, 8, 12 or 16 pixels. (Combinations of these smaller partitions must combine to form 16×16 macroblocks.)

(source : http://en.wikipedia.org/wiki/Macroblock)

Motion prediction is an important area within the majority of modern video codecs describing methods of obtaining motion vectors with which one can predict pixel values from sets of reference pixels, usually in other frames.

The three major picture types used in the different video algorithms are I, P and B. They are different in the following characteristics:

• I‑frames are the least compressible but don't require other video frames to decode.
• P‑frames can use data from previous frames to decompress and are more compressible than I‑frames .A P‑frame ('Predicted picture') holds only the changes in the image from the previous frame. For example, in a scene where a car moves across a stationary background, only the car's movements need to be encoded. The encoder does not need to store the unchanging background pixels in the P‑frame, so saving space. P‑frames are also known as delta‑frames. A B‑frame ('Bi-predictive picture') saves even more space by using differences between the current frame and both the preceding and following frames to specify its content.
• B‑frames can use both previous and forward frames for data reference to get the highest amount of data compression.

http://wiki.multimedia.cx/index.php?title=Motion_Prediction

http://en.wikipedia.org/wiki/Video_compression_picture_types

Aliasing occurs when a signal being sampled contains frequencies that are too high to be successfully digitised at a given sampling frequency. When sampled these high frequencies fold back on top of the lower frequencies producing distortion. In most methods of video digitising, this will produced pronounced vertical lines in the picture. This problem can be reduced by applying a low pass filter to the video signal before it is digitised to remove the unwanted high frequency components. This is tricky to do without removing some of the wanted high frequency components, and results in softer edges in the picture due to the slower permitted transitions in the signal level. See figures 6.2(a) and 6.2(b).

(a)	(b)

Figure 6.2 – (a) Aliasing and (b) Effect of Low-Pass Filtering before Digitising

Blockiness is another artifact that affects JPEG and MPEG. When video footage involving high speed motion is digitised, the individual 8×8 blocks that make up the picture become more pronounced.

Figure 6.8 – Blockiness caused by Compression
Digital Signal Degradation in digital video form degrades far less gracefully than its analogue counterpart. While digital information may in theory be duplicated an infinite number of times without any degradation, once that degradation does occur, it is very noticeable. Due to the compression techniques used, a single bit error in the data stream could for example cause a large block of pixels to be displayed in a completely different colour to that intended.

Figure 6.6 – An MPEG video frame with multiple bit errors

(source : http://www.doc.ic.ac.uk/~nd/surprise_96/journal/vol4/sab/report.html)

design and develop

we starting looking a the brief for the design and develop class

started to look at processing and how to write and reading the code

need to buy
Getting Started with Processing