Re: Massachusetts Amber Alert

[Garrett Wollman <wollman@khavrinen.lcs.mit.edu>]

<<On Fri,  8 Aug 2003 14:39:45 -0400, "rogerkirk" <rogerkirk@mail.ttlc.net> said:

> Garrett Wollman wrote:
>> Cable systems can and should (and I believe are supposed to) use a
>> cherrypicker to insert EAS alerts into their data streams on all
>> channels.

> Cherrypicker?

A cherrypicker (or possibly Cherrypicker(tm)) is a device that does
drop and insert on MPEG streams.

In essence, most cable companies get their network feeds in digital
form, pre-compressed to make the most efficient possible use of
bandwidth.  These feeds are downlinked at the headend and sent over
fiber to remote neighborhood service units which decode the digital
streams into analog video (for basic channels) and transmit the result
over broadband coaxial cable into your home.

Not all of the streams that come down from the satellite will be
offered by the cable company.  The company that does the compression
has lots of mathematics Ph.D.s who figure out the optimal way to fit
the required channels into the available satellite bandwidth.  This
means that some of the streams will include multiplexed data from (for
example) regional sports channels or superstations that are not
carried on a particular local system.  The cherrypicker is used at the
headend to delete the unwanted streams from the multiplex and insert
other content (for example, a local station feed).  At the same time,
it can also drop out network commercials and play local inserts
instead.

-GAWollman