Do I really need to deinterlace a DVD?

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gentleben
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Do I really need to deinterlace a DVD?

Post by gentleben »

I noticed on some UK DVDs containing TV series (such as George & Mildred, Minder, Dame Edna Experience, etc), that sometimes color banding exists in the output file. I'm encoding to Fast 576p25.

I tried toggling various settings to remove the color banding and the one that actually removes it is setting Deinterlace to Off. With deinterlace set to off and everything else at 576p25 preset defaults, there is no color banding.

So my question is, do I really need to use deinterlace on DVDs with TV series?

I'm primary talking about TV series on DVD, not movies. I'm using Fast 576p25 and the purpose of my encoding is just to have a decent quality copy (with a reasonable filesize) of the videos on my computer so that I don't need to keep finding the disc.

From research, I understand that DVDs with TV series are typically interlaced while movies are not. This explains why i have never seen color banding in movie DVDs.

But why do I need to deinterlace TV programme DVDs at all? The video files seem to playback fine. Does deinterlacing improve the video quality (albeit at the expense of possible color banding)? Or does it reduce it?

After I saw that color banding was gone after setting deinterlace to off, I wondered if I need to encode color banded TV programmes again but then I thought, well the deinterlace option is enabled by default for a reason. So I best check first.

Thank you.
Woodstock
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Re: Do I really need to deinterlace a DVD?

Post by Woodstock »

The output is not going to be (handbrake doesn't output interlaced video). So you can often see combing (those bands you mentioned) in the result.

The parameter you probably want to disable is "Comb detection", which tells handbrake to only apply deinterlacing "when needed", while with that disabled, the deinterlace algorithm is applied to all frames.
gentleben
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Re: Do I really need to deinterlace a DVD?

Post by gentleben »

How do I disable comb detection? Do I need to modify the Handbrake start menu shortcut to this:
"C:\Program Files\HandBrake\HandBrake.exe" --no-comb-detect

Or can I do it from the Handbrake interface?

Or do you mean I should set Deinterlace to Decomb (default) and Interlace Detection to Off? Because I tried that and still got the color banding. The only thing that removed it is setting Deinterlace to Off.

Also, you are saying that if the DVD is interlaced, Handbrake will always deinterlace it regardless of the interface settings? So then if Handbrake always outputs deinterlaced video, what is happening when I set the Deinterlace dropdown menu to Off? Surely that disables deinterlacing which surely means Handbrake would output interlaced video?
Woodstock
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Re: Do I really need to deinterlace a DVD?

Post by Woodstock »

On the filters page, you have a number of possible selections relating to telecine and interlacing. Look for "Interlace detection", and set it to OFF.

That will force the interlace removal to be applied to all frames. After that, you can select which deinterlace filter to use. I use "Bob" for most stuff.

Oh, on the Video tab, setting the frame rate to "Variable", and "Same as Source" seems to be advisable for Bob.

DVDs by standard are interlaced. Handbrake outputs non-interlaced video. If you have no deinterlace filtering turned on, the output can end up with a lot more artifacts.
gentleben
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Re: Do I really need to deinterlace a DVD?

Post by gentleben »

Many thanks for your reply. I tried the settings you recommended (Interlace Detection: Off, Deinterlace Filter: Decomb & Bob, Video: Variable Framerate, Same as Source) and the color banding is definitely better.

So I should use these settings for all DVDs (movies and TV programmes)?

One strange thing though. The DVD I tested this out on was The Dame Edna Experience. It's just a regular region 2 PAL DVD (I'm in UK). Like all UK PAL DVDs, it's 25fps. But when I set Handbrake to use framerate same as source, the encoded file is 50fps. Is this normal? Is the 50fps MP4 file that Handbrake produces caused by deinterlacing? Also, since all UK PAL DVDs are 25fps, wouldn't it be better to keep framerate at preset default of 25fps to match the DVD? Although that doesn't explain why Handbrake encodes at 50fps with framerate set to same as source when the source is 25fps.
Woodstock
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Re: Do I really need to deinterlace a DVD?

Post by Woodstock »

Interlaced 25fps is actually two half-frames for each frame, so splitting them up gives you 50fps.
gentleben
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Re: Do I really need to deinterlace a DVD?

Post by gentleben »

I see so deinterlacing a 25fps video will always output 50fps. Given that then, would you still recommend setting fps to same as source? Seems strange to have a 50fps MP4. Is there any quality benefit over 25fps? I mean, if I played the DVD disc directly, it would be 25fps anyway.
Woodstock
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Re: Do I really need to deinterlace a DVD?

Post by Woodstock »

Motion is smoother, in my experience, by going to the "Bob rate". When things are moving, their position in the frame can change between half frames, and double-rate doesn't have to try to blend the two together. But that's just my opinion on it, and I have all my DVD presets using that.
gentleben
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Re: Do I really need to deinterlace a DVD?

Post by gentleben »

I have to say, Woodstock, that after trying your settings on a few DVDs, they look really good and better than before.

So your advice for the best general settings for DVDs is to use the 576p25 preset (I use Fast) and manually set Interlace Detection to Off, deinterlace to Decomb Bob and video FPS to Same as Source (variable)? Is there any other settings I should choose to improve the quality even more?

For deinterlace, would EEDI2 Bob be better than Bob? i don't know if it would be, but the encoding time is massively longer so I'm assuming it's better quality?

I use Quality RF 20 for a decent file size vs quality ratio (the default setting for the Fast 576p25 preset). Is this a good choice?
Woodstock
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Re: Do I really need to deinterlace a DVD?

Post by Woodstock »

I really cannot say if EEDI2 is better or worse, as I haven't played with it. That is the thing, though; you CAN play with settings. You don't even have to do full encodes... Pick a chapter of a video that has a mixture of movement and detail, and encode it with various settings changes. Compare the results. If you're familiar with how opticians work, "Which is better, 1 ... or 2?"

Once you find the settings you like best, just save it as a personal preset, make it your default (if you're doing a lot of DVD stuff at a time), so you do not have to tweak as much later. I have two main presets; one for DVD, and one for BD. The BD preset has all the deinterlace and detelecine stuff turned off (most BDs don't mess with that), while the DVD preset uses the "deinterlace all frames".
gentleben
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Re: Do I really need to deinterlace a DVD?

Post by gentleben »

So your DVD preset is basically 576p25 default but with interlace detection off, deinterlace set to Decomb Bob and framerate set to Same as Source (producing double-framerate files)? You don't change any other settings from 576p25 defaults for your DVD preset?

My optician hates me for never being able to choose 1 or 2, lol, so I just ask him what he thinks is best then I go with that.
Woodstock
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Re: Do I really need to deinterlace a DVD?

Post by Woodstock »

Mine is actually based on the NTSC version, 480p30, but you have the essence. I'm not buying as much PAL stuff on DVD anymore.
gentleben
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Re: Do I really need to deinterlace a DVD?

Post by gentleben »

So if I choose no interlace detection (off), deinterlace decomb bob, and video framerate same as source, there is a choice between constant and variable framerate. Does it matter which I choose? Using same as source framerate produces a 50fps mp4 (PAL UK) so does the default option of variable framerate change this? Or, if i choose same as source, does the framerate change to match the source even during the video (i.e. if the source starts at 50fps but changes to 25fps half way through the video, does the mp4 change also if 'variable framerate' is set?)

I ask because using the above settings, I did have one video where the audio seemed to be slightly out of sync. I wondered if it was to do with variable framerate (i'm using same as source in the video tab as i said).

Thank you.
Woodstock
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Re: Do I really need to deinterlace a DVD?

Post by Woodstock »

I've settled on "VFR, Same as Source" for frame rates. Some devices REQUIRE constant frame rate, as do some popular editing programs. I don't use those, so...

DVDs should be CFR, but they aren't always. VFR/SaS allows the encoder a slight amount of freedom to deal with it, without trying to add/remove frames to meet CFR. As I understand it, and I may be wrong, it also allows the encoder to take two or more identical frames and make them one longer-duration frame.

(this should not affect audio sync)
gentleben
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Re: Do I really need to deinterlace a DVD?

Post by gentleben »

Ah. When you say problematic for some popular editing programs, do you mean programs like DaVinci Resolve? Because I was planning on using Resolve at some point. Is no interlace detection/decomb bob, same as source/CFR still a good idea (instead of default Fast 576p25 preset)?
Woodstock
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Re: Do I really need to deinterlace a DVD?

Post by Woodstock »

Someone who edits video would be far more qualified to answer that than me. I can only echo what I've read here on that issue.

There are "Production" presets intended for converting video to be compatible with editors, and I recall most of those being constant frame rate out.
gentleben
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Re: Do I really need to deinterlace a DVD?

Post by gentleben »

Ah yes, you're right, good point.
damian101
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Re: Do I really need to deinterlace a DVD?

Post by damian101 »

If each two half frames were taken from a single original frame the best thing to do is to turn every deinterlacing filter off and encode to 25 fps. The half frames will just be recombined into a single progressive frame.

If each half frame shows a different point in time, you ideally should use some Bob-style deinterlacer and encode to 50 fps.
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