WTMJ-DT may need a rescan Friday

[oflaherty]

It looks like many people may have to rescan their over the air DTV receivers to get WTMJ-DT Friday afternoon.

Here's why:

For the past few days Time Warner Cable has been using an off-air receiver to get WTMJ-DT on to their cable system.

We would both like to switch over to feeding the WTMJ-DT signal via fiber optic cable.

For the past few days we've been working with the fiber equipment, but audio and video have not been getting through to Time Warner.

The fiber system uses the European Digital Video Broadcasting (DVB) standard to transmit the data. We use the American over the air ATSC system to generate the data. Both systems use MPEG-2 to send video and audio data packets. In both systems every packet of video data and every packet of audio data starts with a packet identifier number, called a PID. That's how the receiver knows which packet goes with which video service and which packet goes with which audio service.

But there are some small differences in the numbering of the ATSC packet ID's and DVB packet ID's.

The numbers that we use for our main video and audio packet ID's are not compatible with the DVB fiber equipment.

So sometime late Friday morning we will probably change the packet ID numbers for our video and audio service.

Once the packet ID numbers change, most over the air receivers will probably have trouble finding the video and audio packets.  We think rescanning may be necessary to get the receivers to find the new packet ID numbers.

And yes, PID'S are a small part of the main PSIP data tables that do lots of other things including setting up the virtual channel numbers (like 4-1).
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Sean at TMJ