Widescreen autodetection - how does it work?


Standard Member
Wasn't sure which thread to post this in but, since it relates to my DVD player...

Why is it that some devices will force a television into widescreen mode when outputting an anamorphic 16:9 picture, when others do not? I have a Philips 28" Matchline Widescreen TV and a Panasonic TH-37PV500B Plasma screen and have observed the following:

Does autodetect aspect ratio:
Xbox 360 (PAL-50,480i, 480p,720i,720p,1080i/YPbPr)
Amstrad Sky Digital Receiver (RGB SCART)

Does not autodetect aspect ratio:
Xbox 360 (PAL-60/YPbPr)
Cambridge Audio DVD77 (480i,480p/YPbPr)
Archos AV5100 (Composite SCART)
Nintendo Gamecube (RGB SCART)

What's odd is that my DVD Player does not switch the TV into widescreen on either TV, despite having 16:9 mode set in its options.

What's even odder is that the Xbox 360 will switch the TV to 16:9 mode in every setting except PAL-60.

And what's odder still is that my original Xbox (now sold on) would sometimes switch and sometimes fail to switch (and that's just the dashboard).

How does this process work (or notwork)?


Distinguished Member
Depending on the connection, this can be carried out in a number of ways.

When using SCART, pin 8 is used to signal the aspect ratio. You can see more details of the voltages involved here.

Component and other connections do not have separate pins, so line 23 switching may be used. You can see more about how this works with this PDF.

In the absence of these, many sets can do their own detection but this will only work for 16:9 pictures letterboxed into a 4:3 frame. They do this by looking at the first few lines of the video signal. If no significant video is detected, the set will assume a 16:9 image in a 4:3 frame and switch accordingly.


Standard Member
Thanks for that - very useful, although some went a bit over my head. Just 2 further questions:

Does this mean that a device is somehow defficient if it does not switch to the correct aspect ratio (like my Cambridge Audio DVD PLayer)?

With a game console, is this something that could/should be managed by software?


Novice Member
AFAIK, DVD players don't actually do widescreen switching as such, you have to set the player to 16:9 or 4:3 manually.

Widescreen DVDs are recorded anamorphically, as you said. As I understand it, when the DVD is mastered, the picture is squashed horizontally into a 4:3 frame. When the DVD is played, the player has to expand the frame to 16:9 (if the option is set in the menus). If you play a 4:3 DVD, that will also get expanded to 16:9.

I suppose that the reason why they can't do auto WS switching is that the player has no idea if the DVD is anamorphic WS or 4:3, since the actual data is the same.
Maybe WS switching was left out of the DVD spec on purpose, to make it a truly international standard. Maybe other broadcast systems don't use line 23 signalling, or is it the fact that line 23 doesn't actually exist on a DVD (it's inside the "overscan" area for PAL 625).

Presumably for scart pin8 switching to work reliably, the device still has to decode the PAL line 23 signal from the original frame.

If I'm wrong about this, will someone please explain how it really works:lease:


Standard Member
I used to have a Panasonic A360 DVD player, and that would detect anamorphic disks and send a widescreen switching signal on pin 8 of the scart. There is a flag in the DVD data on the disc to do this, and every anamorphic DVD I have would automatically set the TV to "Wide."

I've always assumed every player did this, but apparently not. After the A360 died, I've replaced it with the Cambridge Audio DVD89, which doesn't switch the TV. I thought this might be a fault, but apparently that's the way it works - so I have to switch the TV manually. Has anyone got a player that'll do what the DVD89 does but switch automatically?


Carl Stock

Active Member
Hi. :)

From my experience of DVD players and widescreen signalling, not all DVD players employ each method of widescreen signalling. The Cambridge Audio DVD players that I know best (DVD55 and DVD57) do not employ signalling via pin 8 of SCART, which is not uncommon; however, as an example, Thomson and Philips ones do, but of course Cambridge ones do a better job in the terms of picture and sound quality! Sky digiboxes and all Sky+ boxes use pin 8 of SCART as well.

It's not easy to work out whether devices have widescreen signalling via SCART! It's also important to ensure the SCART leads are all firmly plugged in because one of my DVD players would not switch in and out of widescreen properly because the SCART lead will slightly askew in the socket! SCART leads and sockets are a pain! LOL


Carl :)


I ahve the same TV in the bedroom, and it switches at totally random times. There never seems to be any specific aspect that cuases it.

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