Examining MPEG 2,4, and FEC Part 1
Much of what we’ve been told about digital systems is only partially true.
When digital is described as “all or nothing”, this is a generalization based on the upper performance capabilities of digital systems. In fact, most of the things written deal with upper or optimum performance. When expounding on the wonders of digital compression and FEC, most articles are written as if everything is optimized – including the signal received at home.
There is much controversy over digital picture variation. If picture quality didn’t vary, why is there no consensus on the best quality provider? It is because of the variations in the quality of the installation at home that there is no consensus.
I am here to set the record straight.
The key to picture variation is in the MPEG “tool kit”. The tool we are looking for is called SVC (Scalable Video Coding) Extension H.264 of MPEG standards. Previously, this was called Signal-to-noise ratio scaling, or SNR scaling.
It is commonly reported that sending multiple bit streams are for:
1. the capability to reconstruct lost data
2. the ability of all types of reception (mobile, DTV, satellite, etc) to use the same bit stream by having the ability to scale to meet resolution, screen size, etc
This is true.
What has been left out is this:
Scalable Video Coding (SVC) extension H.264 also allows the receiver to scale DOWN in the presence of slow data or a compromised bit stream. “As long as you have lock” isn’t good enough. There are three ways that a picture can be scaled:
1. Fidelity or Quality scaling
This will give you the picture described as grainy or blurry.
2. Size scaling
This is not used in satellite receivers but is used on some televisions.
3. Temporal Scaling (later)
Before getting further into the workings of MPEG and FEC, here are some links to references.
The most direct explanation comes from an article that I found a few months ago.
I found this article from:
IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL. 17, NO. 9, SEPTEMBER 2007
The name of the article is:
“Overview of the Scalable Video Coding Extension of the H.264/AVC Standard”
(Let me just add here that the previous name of SVC scalability was SNR scalability. That’s Signal-to-Noise Ratio Scalability.)
The abstract states it very simply:
Abstract—With the introduction of the H.264/AVC video coding standard, significant improvements have recently been demonstrated in video compression capability. The Joint Video Team of the ITU-T VCEG and the ISO/IEC MPEG has now also standardized a Scalable Video Coding (SVC) extension of the H.264/AVC standard. SVC enables the transmission and decoding of partial bit streams to provide video services with lower temporal or spatial resolutions or reduced fidelitywhile retaining a reconstruction quality that is high relative to the rate of the partial bit streams. Hence, SVC provides functionalities such as graceful degradationin lossy transmission environments as well as bit rate, format, and power adaptation.
Moreover, the basic tools for providing temporal, spatial, and quality scalability are described in detail and experimentally analyzed regarding their efficiency and complexity.
Index Terms—H.264/AVC, MPEG-4, Scalable Video Coding (SVC), standards, video.
Read it for yourself! Very interesting! http://ip.hhi.de/imagecom_G1/assets/pdfs/Overview_SVC_IEEE07.pdf