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A thread below stated the DVI Bravo could produce a better picture than an SDI DVD feeding an outboard scaler because the MPEG in the new

Bravo is better than the one on the older SDI DVD.


Could someone give me a short course on MPEGs? How many different kinds are there? How often do new versions come out? Can they be modified to produce better pictures by a third party or are they impenetrable solid blocks in terms of internal modifications? I know that only those DVDs with "open" MPEGs can have the SDI cable soldered to them.


Given the Bravo results the MPEG seems to be critical in the production chain yet I don't hear very much about them (other than the chroma error).


Thanks kindly.


PS Why would the chroma error have been so hard to correct?
 

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GGA,


MPEG (Moving Picture Experts Group) is basically a set of standards for compressing video and audio. There are many standards, each specificially designed for a particular application. MPEG-2 usually to the compression standard used in DVDs and satellite transmission.


DVDs contain a particular strain of MPEG-2 content embedded in it. The DVD player's job is to decode that content and convert it into video signals. It does this through an MPEG decoder. There are many companies making MPEG decoders. Some are a bit better than others. There are many other factors that decide how good looking the end PQ will look like. The first is the MPEG decoder. After that, there are additional electronics for deinterlacing and converting the video signal into analog formats (component, Svideo and composite) or digital signals (SDI or DVI).


The Bravo apparently has an MPEG decoder that produces a better picture than your garden variety one. However, the deinterlacer is of lower quality. That means you're bound to get a more detailed picture, but with motion and deinterlacing artifacts. In addition, the scaling technology and DVI output is adequate, but the analog is sub-par.


The chroma bug stems from a bug in early designs for MPEG decoders. Apparently, many companies bought the initial design from the same development company. As a result, the error (which I believe comes in two varieties) has gotten into many separate MPEG decoding chips. The error is not that difficult to correct (by either resampling the chroma signal, or by simply not having the bug to begin with). However, it looks like the chips that are without the bug are slowly evaporating. That may mean that we're going to be stuck with the chroma bug for a very long time.


Apparently, it is not financially worthwhile for the companies making these MPEG decoders to go back to the design stage and correct the bug.


Most people, BTW, do not notice the bug until it is pointed out to them. In most situations, the bug doesn't bother me, personally. However, on a LARGE projection screen, the chroma bug(s) can produce the most ugly artifacts you've ever seen. In the last CES, I almost jumped out of my seat during the AVS forum party when Runco demonstrated a stunning projector with a hedious chroma bug issue (attack of the clones was on display).
 

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Quote:
Could someone give me a short course on MPEGs? How many different kinds are there? How often do new versions come out? Can they be modified to produce better pictures by a third party or are they impenetrable solid blocks in terms of internal modifications?
It depends on the type. Some manufacturers have a lot of the process in firmware which can be replaced. Some have replaceable firmware which can simply tweak values on the MPEG chip to get rid of certain bugs. Some are absolutely fixed in the silicon. It really depends on the model and make.
Quote:
I know that only those DVDs with "open" MPEGs can have the SDI cable soldered to them.
SDI is basically a serial version of the parallel data spit out by the MPEG decoder. So, the DVD's data stream gets fed into one side of the MPEG decoder, and the MPEG decoder spits out a stream on the other side which is uncompressed, raw video. Usually, that raw stream goes to additional logic (such as the deinterlacer) or just to a video output section which converts it to Composite, s-video or component to be displayed on your TV. An SDI modification intercepts that raw stream, puts it into a serial format and transmits it to another device (usually a scaler). So, it's basically feeding the scaler raw, uncompressed, digital video.


As long as the MPEG chip spits out this raw data, it should be possible to mod it. As makers try to lower costs, however, more and more of the chip become integrated (i.e. an mpeg decoder and video section in one chip - in this case, there is no raw output from the MPEG decoder...).


-Jon
 
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