John Jay
September 21st, 2003, 12:07 PM
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.
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.