How much does the average TV overscan?

[aamir12345678]

I just need a general answer. About how much % of the horizontal picture does the average 4:3 TV cut off because of overscanning?

[adam]

From what I've read its between 12 and 16 pixels for the average tv. Some may do less then 12 but few do more than 16. As for the percentage? You do the math...my head hurts.

[aamir12345678]

16 out of the 720?

[adam]

Correct, sorry for being ambiguous. That would be 8 pixels on either side. This also happens on top and bottom, but again the exact amount cut off varies from tv to tv.

So for instance if you wanted to ensure that no picture was cut off you could put an 8 pixel border on all sides, but the border may be visible on some tv's.

[mh2360]

Its probably not a "Set in stone " value, its probably depends on the manufacturers quality control (calibration during assembly). I have a JVC 28in widescreen that seens to overscan much more than my Philips 32in widescreen...

[trossin]

DVDLab when set to TV safe mode adds 5% black on the top, bottom, left and right. For 720x480 NTSC that is 36 pixels on the left and 36 on the right and 24 pixels on the top and on the bottom. I can not see these on my TV.

Ulead MovieFactory 2 does a similar amount. Try some experiments and see what different TVs do. Make some photo DVDs with arrows of various widths to see what is going on.

16 just seems small to me. Back when I was a TV repair kid in the 70's the old tube sets and some of the transistor sets had knobs to adjust the overscan. We used to overscan by about 10%. This setting is now done with computers (ok microcontrollers and ASICs) at the factory so it should be pretty similar. I would guess the NAB folks have a spec on this if you really want to find out the truth.

I just dumped out some of the processed images from the authoring tools that I have tried out to get numbers.

[adam]

Well maybe when I read "16 pixels" that is 16 on each side, making it about 32 total just for the sides. But I always thought that's where the 704 active pixels rating came from (720-16=704).

Like I said, I let Fit2disk do all the math for me, so definitely don't take my word for it. I agree, the only way to know for sure what your particular DVD player does is to make some samples and actually watch how much gets cut off.

[skebenin]

A few years ago I tested this on my own TV (using SVCD with varying amounts of black borders). For that particular TV the overscan was approximately 22 (out of 480) on each side and about 28 (out of 480) top and bottom. The exact amount varied over time (more one day, less the next), probably dependent on the temperature or something.

44/480 -> 9.2%
56/480 -> 11.7%

Of course, every TV is different so you can't draw any conclusions from that.

[vhelp]

hmm...

I wonder if there is an "test pattern" pic for this sort of test. I would guess
that this pattern would include resolution tics on the outer most areas, say
around 32 pixels (top/bott/left/right) ..and all one has to do is burn this to a
disk and play in each DVD player being tested. (maybe trev can make up
one ) hmm.. Anyways.

As others have said.., it depends upon the tv or player outputing the final
source materials (hence, cutting off areas of the video)

The only issue to watch out for is.., what if the source you are capping from
is giving the wrong aspect ratio anyways. Then, in that case, you can't know
for sure with 100% accuracy that the method you are using will win your
argument upon proper aspect ratio from a TV's overscan.
.
So, we really need to know for sure, what "approx" resolution these shows
are being outputing as (and as some of you all know, one channel varies
from another's specs, and Provider as well, need to be factored)
.
But, since we can't rely 100% of this, we just do the best we can and
cross our fingers :P

Cheers,
-vhelp

[aamir12345678]

First off, you can use Center (Custom Size) with TMPGEnc. This way, you know what AR the encoder will arrange to.

Second, I always thought that it was the TV that did the overscanning, not the DVD Player...

[guns1inger]

It is the TV and not the player that is the issue here. You also can't guarantee that the overscan will be even on both sides, as the TV itself may not be centred.

I actually find all this discussion about overscan fairly pointless. Unless you are shooting a film for TV broadcast, or creating titles and menus, then overscan is not an issue. If you are, use the title and action safe indicators in your editor to get a feel for how to frame your shots, and shoot accordingly.

Remember that TV programs have been shot to cater for overscan since the dawn of time. If you record a TV broadcast to tape or disc, you will also record the overscan area as well. If you then author this recording into a disc, you get exactly what was broadcast. You don't loose anything, because the program has bee shot to take this into account.

The only time this seems to be a problem for people is when they have downloaded a movie that has been subtitled and poorly cropped, in which case I have no sympathy. Otherwise, you are simply wasting your time adding borders and worrying about a few pixels that the director doesn't expect you to see anyway.

[adam]

I disagree. However many pixels it is, add up all those pixels on all four sides by every frame of every second and so on. By the end of a two hour flick you've actually got a decent amount pixels that will effectively never be seen on a tv. So if you know your video is only going to be viewed on a tv then you can crop and add borders over these pixels. By encoding black picture instead of active pixels, you actually free up a decent amount of bitrate. You'd be suprised how much of a difference this can make, especially with low bitrate encodes. I could literally see the difference back when I made SVCDs.

Since you've also got this area which you can play with (can crop as much or as little as you want of that which will be overscanned, and it won't affect aspect ratio as long as you add borders in a proportional amount) you can made sure you are encoding in mod 16 (all macroblocks =16x16 with no left over pixels). This improves encoding efficiency which improves quality as well as encoding speed.

As for adding borders to try to make those overscanned pixels viewable? No that's pointless if the footage was flimed and edited properly. I was just using it as an example to illustrate the values I listed. But taking overscan into account when encoding opens up a lot of possibilities for optimizing your encode for speed and quality.

As far as producing original content, yeah just keep it in mind when filming and use the titlesafe option in your editor.