Question about caputring VHS and overscan

[kangarooster]

I was reading this website about overscanning. According to the source, overscanned ares are not visible when you are watching the content on a TV. I can understand this if the source has the same aspect ratio as the TV, however:
If VHS 4:3 material is captured, authored for DVD playback, burned and then played on a 16:9 HDTV, it seems that there no way of hiding the overscan on left and right edges? See my image:

So should I crop/add black borders (mask) to cover up a few pixels on the edges (and remove head switching noise) or not?

[jagabo]

Overscan is what a TV does, it's not a property of the video. What you are talking about are the "back porch" and "front porch" of the analog signal.

https://en.wikipedia.org/wiki/Analog_television#Structure_of_a_video_signal

Some players/TVs will simulate overscan and crop those before displaying, some will not. It's best to fill them with pure black before encoding. On you can crop them away leaving a 704 pixel wide frame.

[KarMa]

So should I crop/add black borders (mask) to cover up a few pixels on the edges (and remove head switching noise) or not?

All about taste, really up to you. If you do, I would fill the boarders with pure black instead of cropping to a weird resolution, assuming you want this on DVD. And replace the head noise at the bottom with pure black is you want.

When you burn it to DVD, it will shrink it to 720x576. Then when played on an HDTV, a 4:3 video will be stretched to 788x576 (for 4:3 PAL Material). So keep this in mind, and maybe just keep your VHS captures at 720x576 when you burn them to DVD. Just don't want you taking my advice from your other thread and upscale the video to 788x576 and then put it on DVD which will just shrink it down again, only to be upscaled again.

https://forum.videohelp.com/threads/374875-VHS-capturing-and-resizing-for-correct-AR

[kangarooster]

@jagabo: Thank you for clearing things up

My picture is not centered (I have a few black pixels on each side, but more on one side) so I guess I can crop e.g. 4 pixels from left, and 8 pixels from right (12 in total), then add 6 pixels of black borders to both sides (12 in total). This way the picture will be centered and my resolution and aspect ratio will be kept intact. Or maybe I could crop 8 + 10 pixels and keep it 704x576 since this resolution also works for DVD. I guess it doesn't matter which way I go.

So should I crop/add black borders (mask) to cover up a few pixels on the edges (and remove head switching noise) or not?

All about taste, really up to you. If you do, I would fill the boarders with pure black instead of cropping to a weird resolution, assuming you want this on DVD. And replace the head noise at the bottom with pure black is you want.

When you burn it to DVD, it will shrink it to 720x576. Then when played on an HDTV, a 4:3 video will be stretched to 788x576 (for 4:3 PAL Material). So keep this in mind, and maybe just keep your VHS captures at 720x576 when you burn them to DVD. Just don't want you taking my advice from your other thread and upscale the video to 788x576 and then put it on DVD which will just shrink it down again, only to be upscaled again.

https://forum.videohelp.com/threads/374875-VHS-capturing-and-resizing-for-correct-AR

Thank your for reply. I will keep my resolution at 720x576.

So on a SDTV, the resolution will be 720x576, but since HDTV have square pixels, the resolution is stretched to 788 pixels? So 1 rectangle pixel = 788/720=1.094 square pixels?

[hech54]

I know of at least two softwares (AviDemux and VirtualDub *with BorderControl plugin) that can add black over top of your overscan without the cropping/adding hassle.
You are going to have to re-encode anyway so hey....

[jagabo]

My picture is not centered (I have a few black pixels on each side, but more on one side) so I guess I can crop e.g. 4 pixels from left, and 8 pixels from right (12 in total), then add 6 pixels of black borders to both sides (12 in total). This way the picture will be centered and my resolution and aspect ratio will be kept intact. Or maybe I could crop 8 + 10 pixels and keep it 704x576 since this resolution also works for DVD. I guess it doesn't matter which way I go.

There's a slight difference in picture quality. MPEG 2 encoding uses 8x8 blocks. Having 8 pixel wide borders will give slightly cleaner encoding and better compression.

There's also is a slight aspect ratio difference. Analog video capture normally follows the ITU rec.601 spec which captures the 4:3 video in a 704x480 frame, padded to 720x480. So the full 720x480 frame is slightly wider than 4:3. In MPEG encoding the full 720x480 frame constitutes the 4:3 image. So simply taking your ITU capture and burning it to DVD will result in a ~2 percent aspect ratio error. If you crop the ITU frame down to 704x480 and use that on DVD you will get a more accurate aspect ratio.

Nobody in the industry cares about this small AR difference and it's common practice to just encode the 720x480 frame when making DVDs from analog video tapes. Even DVD players can be schizophrenic regarding this, following the ITU spec at the analog outputs, but using the MPEG spec using the digital outputs.

[KarMa]

There's also is a slight aspect ratio difference. Analog video capture normally follows the ITU rec.601 spec which captures the 4:3 video in a 704x480 frame, padded to 720x480. So the full 720x480 frame is slightly wider than 4:3. In MPEG encoding the full 720x480 frame constitutes the 4:3 image. So simply taking your ITU capture and burning it to DVD will result in a ~2 percent aspect ratio error. If you crop the ITU frame down to 704x480 and use that on DVD you will get a more accurate aspect ratio.

Nobody in the industry cares about this small AR difference and it's common practice to just encode the 720x480 frame when making DVDs from analog video tapes. Even DVD players can be schizophrenic regarding this, following the ITU spec at the analog outputs, but using the MPEG spec using the digital outputs.

Just about every 4:3 DVD I come across comes with black bar padding to follow ITU.


I'd just use a mixture of crop() and AddBorders() in avisynth to get a 720x576 output with straight black boarders, to be put on a DVD.

[jagabo]

Just about every 4:3 DVD I come across comes with black bar padding to follow ITU.

Which is what I said:

Nobody in the industry cares about this small AR difference and it's common practice to just encode the 720x480 frame when making DVDs from analog video tapes.

But if you look at the MPEG 2 spec (the DVD spec refers you to the MPEG 2 spec for aspect ratios) it specifically says the full frame comprises the flagged display aspect ratio.

[kangarooster]

My picture is not centered (I have a few black pixels on each side, but more on one side) so I guess I can crop e.g. 4 pixels from left, and 8 pixels from right (12 in total), then add 6 pixels of black borders to both sides (12 in total). This way the picture will be centered and my resolution and aspect ratio will be kept intact. Or maybe I could crop 8 + 10 pixels and keep it 704x576 since this resolution also works for DVD. I guess it doesn't matter which way I go.

There's a slight difference in picture quality. MPEG 2 encoding uses 8x8 blocks. Having 8 pixel wide borders will give slightly cleaner encoding and better compression.

There's also is a slight aspect ratio difference. Analog video capture normally follows the ITU rec.601 spec which captures the 4:3 video in a 704x480 frame, padded to 720x480. So the full 720x480 frame is slightly wider than 4:3. In MPEG encoding the full 720x480 frame constitutes the 4:3 image. So simply taking your ITU capture and burning it to DVD will result in a ~2 percent aspect ratio error. If you crop the ITU frame down to 704x480 and use that on DVD you will get a more accurate aspect ratio.

Nobody in the industry cares about this small AR difference and it's common practice to just encode the 720x480 frame when making DVDs from analog video tapes. Even DVD players can be schizophrenic regarding this, following the ITU spec at the analog outputs, but using the MPEG spec using the digital outputs.

Thank you for telling me about the 8x8 block thing. Didn't even consider that.

So if I understand you right, there is a small difference between (1) cropping to 704x576 then encoding as 704x576 vs. (2) cropping to 704x576, adding 16 black pixels, then encoding as 720x576? For me it seems that there should be no difference, but maybe I didn't fully understand you

[KarMa]

It would just be kind of weird to see the BBC have it wrong.


episode scene
https://forum.videohelp.com/images/imgfiles/0Fr9cjG.png

[jagabo]

The MPEG 2 spec is very clear about what the aspect ratio flags mean.

[KarMa]

Before I say any more I would like to thank you jagabo for your input and seriously just want to know to know what's proper, even if I don't currently fully take your position. I also have little interest in ever making a DVD in the future, considering all the options we have with media players these days. I just would expect this kind of mistake to be made by no name companies, as 2% AR error is not something any respectable institution could/should really ignore.

All DVDs that I know include bars for 4:3 content
PBS - The Power of Myth on DVD https://forum.videohelp.com/images/imgfiles/7j6WPty.png
PBS - Cosmos with Carl Sagan (I don't have the DVD currently but know they are there)
PBS - The Civil War (I don't have the DVD currently but know they are there)
PBS Nature - Parrots https://forum.videohelp.com/images/imgfiles/nU9nDVw.png (Questar)
School House Rock 2-Disc Set https://forum.videohelp.com/images/imgfiles/zLty0mZ.png
BBC - Louie Theroux episodes (above pic)

I do however have some things that support your idea.
PBS Nature - A Lemars Tail https://forum.videohelp.com/images/imgfiles/e5fNxxW.png (Questar)
PBS Nature - Pale Male (the short opening title scene and intro https://forum.videohelp.com/images/imgfiles/jdOqgCp.png, the actual meat of the program goes to bars https://forum.videohelp.com/images/imgfiles/Z4SpSdJ.png) (Questar)
Napoleon Dynamite - 4:3 Version https://forum.videohelp.com/images/imgfiles/XuN7sOr.png (20th Century Fox)
Under Solen - NTSC version - https://forum.videohelp.com/images/imgfiles/FrSoHTv.png

Even DVD players can be schizophrenic regarding this, following the ITU spec at the analog outputs, but using the MPEG spec using the digital outputs.

Can you expand on this

[jagabo]

I agree with you that most 4:3 DVDs made from video tape were digitized with the rec.601 standard and that the AR was not adjusted when making the DVD.

[KarMa]

I agree with you that most 4:3 DVDs made from video tape were digitized with the rec.601 standard and that the AR was not adjusted when making the DVD.

I had a question at the bottom of my last post.

[Skiller]

I agree with you that most 4:3 DVDs made from video tape were digitized with the rec.601 standard and that the AR was not adjusted when making the DVD.

How would one adjust it anyways? Resize 704 to 720? That would produce too wide an image at the DVD-player's SD analog outputs...

Rec.601 is the only standard in existence for converting SD video between analog and digital. There's no other way to do it.

[kangarooster]

Overscan is what a TV does, it's not a property of the video. What you are talking about are the "back porch" and "front porch" of the analog signal.

https://en.wikipedia.org/wiki/Analog_television#Structure_of_a_video_signal

Some players/TVs will simulate overscan and crop those before displaying, some will not. It's best to fill them with pure black before encoding. On you can crop them away leaving a 704 pixel wide frame.

Does this mean that the overscan area is not part of the 704 frame (i.e. not contained in the active line duration of 52 µs)?

[jagabo]

The amount of overscan varies from TV to TV. In the day of CRTs it could be as much as 10 percent at each edge. So of a 704x480 active picture area as much as 70 pixels at the left and right edges, and 50 pixels top and bottom would be cut off. More typical was about 5 percent. This was because CRTs were not good at keeping the picture the right size and centered. They also suffered from many other geometry problems which were less obvious when you couldn't see the edges of the frame. And all these problems varied from TV to TV, with temperature, age, orientation of the TV, etc. Modern fixed panel TVs don't suffer from these kinds of problems but still overscan by 2 or 3 percent at each edge by default.

[jagabo]

I had a question at the bottom of my last post.

I was referring to the fact that the DVD and Blu-ray players I tested output an analog signal (composite) that corresponded to the rec.601 spec. The 4:3 image corresponded to the 704x480 portion of the frame. But when the same players were upscaling at the HDMI output the entire 720x480 frame was scaled to the output resoulution (1280x720 or 1920x1080). When viewed on an HDTV that did not overscan every pixel of the 720x480 frame was visible. 16:9 discs filled the HDTV screen completely.

I don't remember testing 4:3 discs but I just played a 4:3 DVD which had the entire 720x480 frame filled. I measured the picture on the HDTV screen an it was exactly 4:3. It was not test pattern though so I can't say for sure if the the player (the player was upscaling to 1080p, the TV was not overscanning) cropped the frame down to 704 before upscaling. I'll see if I can come with a test pattern disc to check that. I haven't burned a DVD in years!

OK, I made a 4:3 DVD with an overscan test pattern. The full 720x480 frame was visible on the HDTV screen and the dimensions of the picture between the black pillarbox bars were exactly 4:3. This was using an LG BD670 Blu-ray player.

I dug an old DVD player out of the closet, a Philips DVP-5990. Using the composite output to the HDTV I played the same 4:3 DVD. The TV overscanned the frame (or was it the player? can't tell without some other reference or an oscilloscope) but the test pattern included what should render as a square with MPEG scaling (310x276 pixels in the 720x480 frame). On screen the square measured 35.7x35.0 cm -- 2 percent wider than tall. That's consistent with ITU scaling at the composite output -- assuming the TV is using ITU scaling.

[kangarooster]

I just thought of something. Since 52µs*13.5MHz = 702, wouldn't it be better, AR wise, to squeeze the image 2 pixels (of course you should add black borders to so that the final width is 704/720)? Then again the height is rounded up to 576 from 575, so it might not matter much.

addborder(1,0,1,0) #I don't think this will not work because the values need to be mod 2
BicubicResize/LanczosResize(720,576) #My capture size. Now the image will be squeezed 1 pixel on each side.
crop(x,0,y,0) #where x+y=16 to get 704 width (or keep it at 720)

[jagabo]

You can crop and resize in one step with the resize functions. And they will let you chose odd crop values.

But still, I wouldn't bother. You can't really see a 2 percent or less AR error. And every resize will introduce some artifacts.

[KarMa]

Maybe you could just send them a MP4/MKV copy over the internet and not deal with the DVD, it's 2015. The could just play it on a computer, tv media player, or a bluray player.

[LMotlow]

Maybe you could just send them a MP4/MKV copy over the internet and not deal with the DVD, it's 2015. The could just play it on a computer, tv media player, or a bluray player.

Right. I'd tell the guy just throw his TV out the window. Nobody should be watching broadcast TV -- hell, they use MPEG for broadcast and even have the nerve to use it for retail DVDs and BluRays. Can you believe charging cable money for that crap? He can cut off his cable TV service and save a bundle. The O.P. should convert all of his retail discs to low-bitrate MP4, deinterlace all of it, and watch only on a PC. Everybody knows that converting anything to mp4 or mkv automatically improves it. DVD? BluRay? TV? They're history, dude.

[KarMa]

Maybe you could just send them a MP4/MKV copy over the internet and not deal with the DVD, it's 2015. The could just play it on a computer, tv media player, or a bluray player.

Right. I'd tell the guy just throw his TV out the window. Nobody should be watching broadcast TV -- hell, they use MPEG for broadcast and even have the nerve to use it for retail DVDs and BluRays.

They use MPEG2 for terrestrial US broadcasts and all DVDs. A video standard from the mid-90s, heavily based on the earlier MPEG1. But most Blurays are done with H.264 video nowadays. You do know H.264 is part of MPEG right?

Can you believe charging cable money for that crap? He can cut off his cable TV service and save a bundle. The O.P. should convert all of his retail discs to low-bitrate MP4, deinterlace all of it, and watch only on a PC.

Firstly he is dealing with a VHS capture (lossless?) at 720x576, not a DVD. Maybe you should read the thread. And he can keep his capture with the interlacing for archiving if he wishes, and give out the MKV(H.264) or MP4(H.264) or DVD(MPEG2).

Did I say use a low bitrate MP4 (H.264)? Use a quality deinterlacer like QTGMC, giving 50fps, x264 with a low CRF, and one of the slow x264 presets. I would think QTGMC would give better deinterlacing than any on the fly hardware deinterlacer in your HDTV.

Everybody knows that converting anything to mp4 or mkv automatically improves it. DVD? BluRay? TV? They're history, dude.

I'm starting to believe you think MP4 or MKV is a video format. I just said MP4/MKV to be simple concept for OP.