[MEncoder-users] Re: to crop or not to crop for DVB sources, aspect ratio issues?

[Mark Himsley]

On 11 February 2007 16:12 +0100 Pierre Catello wrote:

> I'm having another problem when cropping: some channels, with full 576
> lines resolution, have some crap on the first line (a black & white
> dotted pattern) likely timecode info encoded on the first line.

Not relevant to mencoder, but that black and white dotted pattern is often 
inserted by pro and semi pro camcorders, and some studio video tape 
recorders, to indicate whether the recording is supposed to be 4:3 or 16:9. 
Some TVs can understand that signal and display the video appropriately.

The signal actually only occupies the first half line of picture. In 
traditional analogue broadcasts the first half line of picture is always 
black. In the digital world we get to be able to use the first half line 
and last half line of the picture, hence the active picture is 576 lines 
and not the expected 575 lines we could use in analogue transmissions - the 
other 25 lines per field being field blanking.

Unfortunately, in my experience at BBC News, the majority of recordings 
indicate 4:3 when the contents is in fact 16:9. Broadcasters are *supposed* 
to blank out this half line before it gets to the transmitters, but not all 
studio vision mixers do.

-- 
Mark Himsley