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Old September 21st, 2003, 12:07 PM   #1
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A New Broadcast Standard?

Having recently installed a DVB card in one of my PCs, I have been investigating what the broadcasters are sending out via satellite.

In deciding which broadcaster to analyse I have chosen the BBC, since everyone knows who they are and besides the've been in the business over fifty years.

To cut a long story short, even though the symbol rate is 27,500,000 the BBC1 mpeg2 stream varies from 300,000 bytes per sec to 500,000 bytes per sec, dependent upon content from a news program to a football match (low motion to high motion content) and based on half hour samples.

After demuxing I was interested to see if this stream is DVD compliant, and sure enough my DVD authoring app accepted these assets. This means the colour space is 4:2:0, the resolution is 720 x 576 interlaced at 25 fps.

You can imagine the size and cost of a pedestal mounted studio camera (with CCDs the size of your back yard) used for either news or sports and yet despite all this what is delivered to the customer is 500kbytes/sec max!. Placed in perspective the DVD specification is about 1200kbytes/sec max.

A LOT of information is therefore discarded through the compression process. To my eyes the most relevant indications of a high end camera in use through observing this compressed footage are twofold

1 much reduced aperture correction (edge enhancement)
2 A very low video noise floor

Perhaps it is these attributes which we should be asking the manufacturers to make improvements upon in future cams rather than enhancements which will be discarded at the compression stage.

It is little wonder why the BBC are using PD150 more extensively for news gathering.
John Jay

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Old September 21st, 2003, 12:28 PM   #2
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What about:
more accurate color reproduction
better low light performance
more control over depth of field
better lenses
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Old September 21st, 2003, 12:31 PM   #3
Join Date: Mar 2002
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Much higher signal to noise ratios have always been a feature of higher end cameras. Noise plays havoc with compression and causes increased data rates. I just don't think the manufactures are going to improve this critical area in prosumer cameras right away. If you want the enhanced feature sets, you're going to have to pay for them in the pro models. The smaller chips (at this time) just don't have what it takes.
Jeff Donald
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Old October 5th, 2003, 03:40 PM   #4
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The BBC is using some very bad compression. It has the lowest
bitrates I've ever seen in a DVB broadcast. 1.5 mbits is not
uncommon it seems.

There are special tools available to easily convert a DVB file
to DVD. I think one was called DVB2DVD <g>

Rob Lohman, visuar@iname.com
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