Examining MPEG 2,4, and FEC Part 1

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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.

And,

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

Also:
Scalable Video Coding – Wikipedia, the free encyclopedia
H.264/MPEG-4 AVC – Wikipedia, the free encyclopedia

10 Comments
  1. rabbit73 says

    Thanks for clarifying the apparent disparity between these two schools of thought, using the concepts of SVC and QEF:
    1. “If all the errors are corrected then the picture must be optimum.”
    2. “I have a good lock on a strong signal but the picture doesn’t look as good as usual.”

    I especially like these two pages on your site:
    Signal and HDTV
    Signal Meters & Bit Error Rate

    1. highdefjeff says

      I do hope that we are in agreement on this subject. H.264 is just the tip of the iceberg in understanding FEC.

      Please, if anyone has a question or doesn’t understand some of this, let me know. If any of you don’t understand this, then there are others who also need more information or explanation.

      Part 2 will be coming shortly, Lord willing.

      Remember that QEF is Quasi Error Free with “Quasi” meaning “reasonable facsimile of” error free. It actually means that at the QEF the Forward Error Correction/Concealment (FEC) is working with enough signal to begin faking it at a level that most people will not be able to tell (especially if they aren’t looking) that there are still many errors going on.

      SVC extension H.264 is picture quality in relation to a certain type of corrupted signal. There are other corruptions of signal (and thus quality) that don’t involve the entire picture at once.

  2. EscapeVelocity says

    I suspected there was some way of sending less than pristine data to the panel for display, and that holes in the image information were being filled by the video processing. But this makes sense as well.

    1. highdefjeff says

      What you say is also true EV.

      FEC conceals whatever it can’t correct. When data is missing, data from a “the pixel next door” is used. The FEC interpolates or guesses the best match. Just how close the match is will determine whether you see it or not.

      Additionally, corrupted or missing data causes lip sync, or garbled Closed Captioning, and even the function of your DVR.

      We’re talking digital and GIGO applies. FEC just masks most errors from view.

      I amended my previous post (as you were posting) suggesting as much.

      1. Fringe Reception says

        highdefjeff wrote above:

        FEC conceals whatever it can’t correct. When data is missing, data from a “the pixel next door” is used. The FEC interpolates or guesses the best match. Just how close the match is will determine whether you see it or not.

        Additionally, corrupted or missing data causes lip sync, or garbled Closed Captioning, and even the function of your DVR. …
        ————————————
        Jeff,

        Please continue with this topic when you have the time. All last summer I experienced lip sync issues watching RTV and it has been corrected.

        However, last summer a local retired Broadcast Engineer who personally knows the head RTV Project Engineer sternly corrected me, when I ‘complained’ (I pointed it out on a different forum) about the lack of care our local RTV affiliate seemed to have regarding their non-synched transmissions … and he put it back to the source … RTV.

        So, apparently it can also boil down to garbage in = garbage out? Imagine that! LOL!

        Jim

        1. highdefjeff says

          Thanks Jim!

          I hope to continue this train of thought as the Lord leads.

          In digital systems, there aren’t very many short answers. I think the best way to discuss this is to expose some of the related myths and establish a firm foundation that we could allbuild on.

          With analog signals, many or all of the “cause and effect” relationships were known and understood. These relationships gave us the ability to effectively diagnose and fix problems. These relationships have been lost to most people in the transition to digital signal.

          Part of the reason is that we dropped everything we knew from analog because we were initially told that it was “all-or-nothing”. From the outset, digital was sold to us as the answer to the old problems of ghosting, static, fading, etc. Since we expected no problems, we looked for no problems.

          The reality is that digital is only more robustat handling previous issues (due to the ability of digital processing and forward error correction/concealment).

          Nothing changed in the physics and properties of the waves we use, just as FOXTV has said previously. Further, digital isn’t new. Tesla developed a remote control boat that was digitally controlled and using a telegraph is digital.

          Here is the short story of the difference between analog and digital. Analog information is continuous. Digital is is not.

          Digital isn’t a new way of broadcasting. Digital isn’t a NEW signal. Digital is most accurately explained as a new type of modulation, not a new creation.

          Now, since so many have seen that picture quality does vary (wholly or in little bits), everyone should dust off what they knew about analog because “only the names were changed to protect the innocent”…or protect something…

          With everyone’s help, we can establish new causal relationships in the digital realm and simplify troubleshooting and correction.

          P.S. What is RTV?

  3. EscapeVelocity says

    Yes, with a 1080 display, you are unlikely to see the errors, if filled with pixel next door or even more advanced video processing techniques, unless the errors get to be huge.

    That is why you see massive pixelation blocks of solid colors, when the picture breaks up. The video processing is trying to compensate.

  4. Fringe Reception says

    highdefjeff,

    Thanks for the comeback and I am enjoying learning from you. :bowdown:

    RTV is the renamed RTN Network, “Retro-TV” that runs many 1960s and 1970s shows from Mike Hammer and Perry Mason to Adam-12 and Battlestar Galactica.

    No, its not ‘Room-Temperature-Vulcanizing-silicone-rubber” that I use to waterproof my outdoor ‘F’ Fittings!!!
    Jim

    1. highdefjeff says

      Thanks Jim, you’re makin’ me laugh!

      I really appreciate your comments, and all of the comments on this forum. WOW! I’m happy and blessed to be here. I haven’t experienced anything like it.

      I can’t take any credit, though. Without the Lord, I wouldn’t know any of this or have been led to this forum. All glory goes to my Father in heaven!

  5. ProjectSHO89 says

    Retro TV….

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