[mythtv-users] PVR 350, closed captioning, commercial detection

[chris at cpr.homelinux.net]

On Mon, Aug 08, 2005 at 08:57:28AM -0400, Scot L. Harris wrote:
> On Mon, 2005-08-08 at 01:05, Jesse D. Guardiani wrote:
> > Also, what about commercial detection? Is that supposed to work with
> > PVR-x50's, or not? If it is, then I'd love to figure out what I need
> > to change to make it work on my system.
> Commercial detection works just fine with my box which has a PVR-350 and
> a PVR-250 in it. 

Commercial detection is not dependent on the type of input device.  The
success rate varies depending on the station, though, as many are now
taking active steps to foil commercial detection.

There are (or were, anyway) at least five ways to detect commercials:
(1) Networks used to insert a countdown signal in the pre-scan region at
the top-right of the screen.  It was a little white box that would
blink and then go solid just before the commercial.  The regional
stations would use that as a guide for inserting local-run commercials.
I don't think that system is used any more.
(2) Some shows used to carry the time signal above frame where CC is now
located, so you could watch for a break in the time signal.  I don't
know if it's still there or not.
(3) There is usually a few frames of black and silence between shows and
commercials and between commercials.  It's easily detected.
(4) Many stations use a "watermark" in the lower right corner of the
screen so you'll always know what station you're watching (or where the
recording came from).  That dissappears during commercials.
(5) Commercial sound levels are usually a few dB louder than the show
they are breaking.  Stations don't care if you fall asleep during the
movie as long as the first thing you see when you wake up is a beer
commercial. :-)

AFAIK, MythTV detects using #3 and #4.  Some stations are running the
commercials closer together to eliminate the breaks, or at least time
the first one to cut into the show.  My MythTV usually misses the first
commercial because there's no blanking, but catches the second one.

MyTH's commercial detection tends to break down during the last break
before the end of the show.  Many stations will run 3 or 4 minutes of
commercials and then come back for the closing statement (or
cliffhanger) and then roll credits.  Myth can see the breaks but can't
tell which are commercials and which are the show because the final show
segment is too short.