[mythtv-users] PVR150: Automatic removing black bar(s) from the recording
beww at beww.org
Tue Mar 27 23:53:56 UTC 2007
On Mar 27, 2007, at 5:23 PM, Ma Begaj wrote:
> I have black bars around mpeg recordings. They are not shown if played
> in MythTV, but MPlayer shows these. I read the IVTV mailing list, and
> moste of the people say this:
> "This is probably just in the source signal. A TV will overscan the
> signal by 4% or more, so broadcasters can put whatever junk they want
> at the edges of the pictures and most people will
> never see it.
Then "most people" are full of crap.
As is usual with faulty statements, there is a kernel of truth there.
Most TV sets do in fact overscan, the main reason being so that as
the set ages and capacitors get leaky and scan voltages drop the
picture will still cover the entire viewable area of the screen,
resulting in a higher perceived "reliability" of the set. People will
decide the set is "broken" if they can see the picture edges but, as
you said, usually don't notice the overscan.
There are actually SMPTE-defined "safe action" and "safe title" areas
of a TV picture, so that titles and action will not be placed where
they might be missed on a typical consumer screen.
Unfortunately neophyte directors, editors and other technical types
are either unaware of these accepted standards or simply don't care.
This is especially true with non-broadcast networks or even broadcast
stations in small markets.
Professional monitors actually have an "underscan" button to reduce
the picture to less than the screen size so that the director is
certain he can see the entire image.
Information is put into the vertical interval (the black bar at the
top of the screen) This includes closed captioning on line 21 and
various test signals used for remote control of transmitters and
video testing being on lines 15 through 19.
No information is put into the horizontal blanking area (to the right
and left of the picture), at least in western nations (some Russian
satellite transmissions encode audio into the horizontal blanking, or
at least used to).
Too wide blanking is a common problem, it used to result in a large
fine from the FCC if you got caught, but you can get away with just
about anything these days.
All this refers to analog video, but even if transmitted digitally
most video these days originated as analog, very few actual digital
cameras and program chains are in use. This will of course change
> Is it possible to remove these lines during transcoding? I give my
> recordings from time to time to my cousin, and I would like to have
> the video without these black bars.
The usual way to correct wide blanking at a TV station is to use a
"DVE" (digital video effects) unit like an Ampex ADO, Tektronix
Kaleidoscope or similar device. Nothing like that is remotely
affordable by consumers though. Once you get out of the accepted
blanking intervals video systems consider the signal as "picture" and
I don't think transcoding would help.
If Myth doesn't have the problem and mplayer does you could probably
adjust mplayer's parameters to do what Myth does though.
beww at beww.org
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