Aspect ratio signalling at DVinfo.net

Andre De Clercq · March 26th, 2006, 01:55 PM

When anamorphic footage is played back with the GS400 it also outputs WSS, so that a Widescreen TV is automatically switched to 16:9. The new GS300/500 can also playback anamorphic footage in letterbox mode (needed for correct viewing on a 4:3 TV). Does somebody know if the WSS code for "letterbox" is being outputted in the latter case too?

Stephen Finton · March 28th, 2006, 09:27 AM

Quote:

Originally Posted by Andre De Clercq

When anamorphic footage is played back with the GS400 it also outputs WSS, so that a Widescreen TV is automatically switched to 16:9. The new GS300/500 can also playback anamorphic footage in letterbox mode (needed for correct viewing on a 4:3 TV). Does somebody know if the WSS code for "letterbox" is being outputted in the latter case too?

I think you got it backwards. The TV sends aspect info. If the camera does not receive it, then it letterboxes its output.

Andre De Clercq · March 28th, 2006, 12:30 PM

I don't think so Stephen. There is only an Y/C connection which is unidirectional. My GS 400 e.g. has a code on line 23 on the analog Y signal when it plays back anamorphic video. This code is being interpreted by my TV and switches it to "full". Unfortunately I cannot insert the (standarized) code for letterbox video. Broadcaster do though,

Stephen Finton · March 28th, 2006, 03:04 PM

Quote:

Originally Posted by Andre De Clercq

I don't think so Stephen. There is only an Y/C connection which is unidirectional. My GS 400 e.g. has a code on line 23 on the analog Y signal when it plays back anamorphic video. This code is being interpreted by my TV and switches it to "full". Unfortunately I cannot insert the (standarized) code for letterbox video. Broadcaster do though,

You're trying to letterbox on a 16:9 screen? Whatever for?

Andre De Clercq · March 29th, 2006, 08:36 AM

When I make VHS copies from amamorphic footage for people not having DVD, they are made in letterbox for correct playback on a 4:3 TV.
Some of those them may have, or buy later, a widescreen TV. I want them to be able to playback their VHS (letterboxed) copy automatically switched to full screen. Therefore I want the VHS copies flagged as "letterbox".

Stephen Finton · March 29th, 2006, 05:06 PM

Quote:

Originally Posted by Andre De Clercq

When I make VHS copies from amamorphic footage for people not having DVD, they are made in letterbox for correct playback on a 4:3 TV.
Some of those them may have, or buy later, a widescreen TV. I want them to be able to playback their VHS (letterboxed) copy automatically switched to full screen. Therefore I want the VHS copies flagged as "letterbox".

I don't think that's possible. I wish someone else would chime in but I believe the "flagging" you are referring to is purely digital and would not be a part of a VHS tape's options. I don't think VHS can even hold time code, that's why you can reset the timer on all those VHS decks out there. There is nothing there other than video signal.

Nick Jushchyshyn · March 29th, 2006, 06:46 PM

Here's a PDF tech doc on WSS flagging:
http://www.intersil.com/data/an/an9716.pdf

The flag is a digital signal embedded into the analog carrier on lines 20 and 283 of an NTSC frame so an widescreen TV that detects the signal on a letterboxed 4:3 tape would automatically crop out the black bars.

In theory, this might show up as a visible pattern on lines 20 & 283, so maybe you could capture this of a pre-encoded VHS tape and overlay it into your video? It might even be possible to calculate the pixel values to create an image based on the tech document.

Well, perhaps. Just a thought.
Good luck.

Andre De Clercq · March 30th, 2006, 03:21 AM

Thanks Nick, I will further report on the MSP forum (andre)

Stephen Finton · March 31st, 2006, 03:45 PM

Quote:

Originally Posted by Nick Jushchyshyn

Here's a PDF tech doc on WSS flagging:
http://www.intersil.com/data/an/an9716.pdf

The flag is a digital signal embedded into the analog carrier on lines 20 and 283 of an NTSC frame so an widescreen TV that detects the signal on a letterboxed 4:3 tape would automatically crop out the black bars.

In theory, this might show up as a visible pattern on lines 20 & 283, so maybe you could capture this of a pre-encoded VHS tape and overlay it into your video? It might even be possible to calculate the pixel values to create an image based on the tech document.

Well, perhaps. Just a thought.
Good luck.

283 will not appear on a 240 line signal. VHS does not have the resolution to support it, even if it is theoretically possible.

Why am I such a pessimist? Sheesh!

Andre De Clercq · March 31st, 2006, 04:40 PM

The frequency spectrum needed for this flagging (not the build-up clocking) has been chosen so that standard VHS passes these signals. NTSC is a 525 line system. not to be confused with 240 TVL/pH VHS resolution. Lines 20 and 283 are placed before the start of the active video content in the vertical blanking interval.

March 26th, 2006, 01:55 PM	#1
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	Aspect ratio signalling When anamorphic footage is played back with the GS400 it also outputs WSS, so that a Widescreen TV is automatically switched to 16:9. The new GS300/500 can also playback anamorphic footage in letterbox mode (needed for correct viewing on a 4:3 TV). Does somebody know if the WSS code for "letterbox" is being outputted in the latter case too?

March 29th, 2006, 06:46 PM	#7
Nick Jushchyshyn Major Player Join Date: Feb 2004 Location: Philadelphia, PA, USA Posts: 548	Here's a PDF tech doc on WSS flagging: http://www.intersil.com/data/an/an9716.pdf The flag is a digital signal embedded into the analog carrier on lines 20 and 283 of an NTSC frame so an widescreen TV that detects the signal on a letterboxed 4:3 tape would automatically crop out the black bars. In theory, this might show up as a visible pattern on lines 20 & 283, so maybe you could capture this of a pre-encoded VHS tape and overlay it into your video? It might even be possible to calculate the pixel values to create an image based on the tech document. Well, perhaps. Just a thought. Good luck. __________________ Nick Jushchyshyn Matchmoving, Compositing, TD imdb

March 28th, 2006, 12:30 PM	#3
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	I don't think so Stephen. There is only an Y/C connection which is unidirectional. My GS 400 e.g. has a code on line 23 on the analog Y signal when it plays back anamorphic video. This code is being interpreted by my TV and switches it to "full". Unfortunately I cannot insert the (standarized) code for letterbox video. Broadcaster do though,

March 29th, 2006, 08:36 AM	#5
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	When I make VHS copies from amamorphic footage for people not having DVD, they are made in letterbox for correct playback on a 4:3 TV. Some of those them may have, or buy later, a widescreen TV. I want them to be able to playback their VHS (letterboxed) copy automatically switched to full screen. Therefore I want the VHS copies flagged as "letterbox".

March 30th, 2006, 03:21 AM	#8
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	Thanks Nick, I will further report on the MSP forum (andre)

March 31st, 2006, 04:40 PM	#10
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	The frequency spectrum needed for this flagging (not the build-up clocking) has been chosen so that standard VHS passes these signals. NTSC is a 525 line system. not to be confused with 240 TVL/pH VHS resolution. Lines 20 and 283 are placed before the start of the active video content in the vertical blanking interval.