DVD - part Interlaced, part Progressive(???)

[pooksahib]

Hi. I'm slowly teaching myself about the various options in Handbrake and currently I'm on Deinterlace and Decomb. Apparently I should use one of these options if I have interlaced video.

I have this DVD with 5 VOBS. The end of VOB-4 and all of VOB-5 are trailers (that may or may not be relevant). Using mediainfo, I see that VOBs 1-4 are interlaced and VOB-5 is progressive. How is that possible, should they not all be the same?

[manono]

How is that possible, should they not all be the same?

No. They can be anything and everything. They can switch from progressive to interlaced every GOP if they like. You should see some anime DVDs which switch from progressive to interlaced encoding quite frequently. I take it that, even though you're in the UK (where most DVDs are encoded as interlaced) you're working with an NTSC DVD?

Besides, MediaInfo is only telling you what the first frame's encoding is like. It says nothing about the rest of those four VOBs. That is, it doesn't parse the DVD. If you want to really know what the DVD is like, open the VOBs in DGIndex and pay attention while running the Preview.

[LigH.de]

From my practical experience in a DVD authoring studio, you will almost always have MPEG-2 video with "interlaced" encoding in DVD Video, no matter whether the video content is progressive or interlaced. That's simply a safety setting: Encoding progressive material in interlaced encoder mode is just not so efficient; but encoding interlaced video material in progressive encoder mode would be a disaster, quality-wise. Progressively encoded material in DVD Video is rare. I remember "Animatrix" as an exception.

The structure of a DVD Video is complex. VOB files as they are authored have little relevance. The important structure parts with "same attribute" rules are the logical Titles and Program Chains (PGC). They can be only a small part of a VOB, as well as spread across several VOB segments. Without analyzing the related IFO files, you will have a hard time understanding the VOB files alone. MediaInfo certainly does not read IFOs. It does not even read the first frame, only headers describing the video stream.

[pooksahib]

Hi manono. No, mediainfo states PAL for all 5 VOBs. I'll look into DGIndex (would GSpot do the same thing?) but in the meantime, would you agree that using Handbrake's 'Decomb - default' is the best bet for this DVD?

Thanks for your time.

[pooksahib]

Hi LigH.de. We posted simultaneously. Thanks for your time, too. Perhaps leaving Decomb activated all the time is the best option...

[LigH.de]

GSpot is even less useful than MediaInfo, regarding DVD Video material. DGIndex instead does decode the video stream, and it does report details of this video stream in a statistics window.

Because it is a PAL DVD, it will not have video material with Telecine, therefore the only method which is most probably not helpful would be IVTC. But apart from that, every trailer may have different issues, or none at all. Trying to deinterlace progressive material will reduce its quality unnecessarily.

Never trust in encoding flags. Always look at the bobbed video and discover the temporal progress if you want to be certain if you need to deinterlace at all. Remember, you might have progressive video already, just the encoding mode was set to "interlaced", but that only encodes fields separately, the timestamps of both fields of a frame are still identical.

[manono]

No, mediainfo states PAL for all 5 VOBs.

PAL, eh? Interesting, since most PAL DVDs are encoded as interlaced. In any event, as LigH.de says, you have to examine the fields and frames and not rely on what MedianInfo tells you. If you don't see any interlacing with a basic AviSynth script opened in VDub, then it's not interlaced. And even if you do see interlacing, it still may not be interlaced (only phase-shifted fields). And that why it's often a good idea to separate the fields or bob the video - to see if each field is unique or if they come in pairs from the same moment in time.

[pooksahib]

PAL, eh? Interesting, since most PAL DVDs are encoded as interlaced.

Hi again. I'm not sure what you're getting at - the first four VOBs (according to mediainfo) ARE interlaced.

[hello_hello]

Hi. I'm slowly teaching myself about the various options in Handbrake and currently I'm on Deinterlace and Decomb. Apparently I should use one of these options if I have interlaced video.

I have this DVD with 5 VOBS. The end of VOB-4 and all of VOB-5 are trailers (that may or may not be relevant). Using mediainfo, I see that VOBs 1-4 are interlaced and VOB-5 is progressive. How is that possible, should they not all be the same?

Doesn't Handbrake have an option to open a folder's worth of files, or to open the files as a complete DVD? I'm pretty sue it does, and it might pay to select the folder containing the ripped DVD files as the source. If you do, you should be able to select the start and end points for encoding, probably by chapter. If some of the video in the vob files is actually interlaced and some progressive (it contains a movie followed by DVD extras, that sort of thing) it'd be a good idea to encode each individually.

If a video really is interlaced, ideally you'd deinterlace it to full frame rate. That's 50fps progressive for PAL. Motion will look smoother than deinterlacing to 25fps. In order to output 50fps with Handbrake you need to set it correctly. I haven't used Handbrake for quite a while so to refresh my memory and give you an idea what to expect I encoded a small sample of interlaced PAL video (500 frames) with different settings to see what would happen.

Decomb filter enabled (default), output a constant frame rate of 50fps. From the log file:
[21:27:10] sync: got 501 frames, 500 expected
[21:27:10] decomb: deinterlaced 147 | blended 51 | unfiltered 302 | total 500
[21:27:10] render: 1000 frames output, 0 dropped and 500 duped for CFR/PFR

That's pretty standard for the Decomb filter. It deinterlaces with either Yadif or by blend deinterlacing. If a frame looks progressive (no combing), it leaves it untouched. Because the Decomb filter deinterlaces to 25fps by default though, Handbrake had to duplicate every frame to output 50fps, which makes 50fps fairly pointless.

Decomb filter enabled (Bob), output a constant frame rate of 50fps:
[21:30:02] sync: got 501 frames, 500 expected
[21:30:02] decomb: deinterlaced 294 | blended 102 | unfiltered 302 | total 698
[21:30:02] render: 1000 frames output, 0 dropped and 302 duped for CFR/PFR

The main difference is "Bob" tells the Decomb filter to deinterlace to 50fps. There were still 302 frames considered to be progressive and were therefore unfiltered and they needed to be duplicated for a 50fps output. Not that it matters in respect to smoothness of motion as there shouldn't be any motion where the frames appear progressive and motion should look smoother where the frames are deinterlaced.

Deinterlace filter enabled (Bob), output a constant frame rate of 50fps:
[21:31:20] sync: got 501 frames, 500 expected
[21:31:20] render: 1000 frames output, 0 dropped and 0 duped for CFR/PFR

Setting the De-interlacer to Bob causes the de-interlacer to output 50fps. Every frame is de-interlaced whether it needs it or not.

Personally, I preferred the look of the third encode even though deinterlacing tends to blur a little. At least it was consistent.
In theory Decomb (Bob) should look better than Deinterlace (Bob) because the Decomb filter only deinterlaces the frames that need it and therefore the rest won't be blurred, but in practice it misses too much combing for my taste (at least for my test sample) which means some of the frames treated as progressive really should have been deinterlaced.

The above only applies to sources that really are interlaced. For progressive PAL there's no need for the Decomb or Deinterlacing filters, although there can be other issues for PAL sources. A couple of times I've come across a PAL DVD created using euro-pulldown, and there's the possibility of phase shifted fields mentioned previously that can make progressive video appear to be interlaced. I'm not sure how well Handbrake's filters would deal with that sort of thing.

[hello_hello]

PAL, eh? Interesting, since most PAL DVDs are encoded as interlaced.

Hi again. I'm not sure what you're getting at - the first four VOBs (according to mediainfo) ARE interlaced.

Don't pay any attention to MediaInfo. Progressive video can be encoded as interlaced, but that doesn't mean it requires deinterlacing. You need to check yourself. Run some small test encodes if need be.
One method of checking if you can't examine the source before encoding it might be to enable the Deinterlace (Bob) filter and make sure the output is set to a constant frame rate of 50fps. Encode a sample, open it in a player and step through it one frame at a time. If most of the frames are unique then the source was probably interlaced. If however, it appears that every frame is repeated, the source is probably progressive.

It's quite possible video on a PAL DVD could be interlaced in places and progressive in others. Mostly it's one or the other, or a movie might be progressive while the DVD extras are interlaced etc, but anything's possible. If a video is mostly progressive with some interlaced sections that might make it a candidate for Handbrake's Decomb filter. The default setting should leave the progressive stuff alone and only deinterlace where it's needed. I'd still set the output to constant frame rate myself, but to 25fps or "same as source" if the majority is progressive.

[pooksahib]

Thanks for that, hello_hello. I never knew this subject could be so complex...

[manono]

PAL, eh? Interesting, since most PAL DVDs are encoded as interlaced.

Hi again. I'm not sure what you're getting at - the first four VOBs (according to mediainfo) ARE interlaced.

Maybe, maybe not. There can be a difference between how it's encoded and what the content is like. The only reliable judge is your eyes, looking at the frames and then the fields, separated or bobbed, as already suggested. If you can't figure this out yourself then post a short 10 second sample, one with steady movement. If this is a film, then it didn't start out life interlaced. The content might be progressive, might be phase-shifted and only appear to be progressive (and using a deinterlacer will seriously degrade it), or might be the victim of a poor film to PAL conversion, in which case unblending it will be way better than just blindly deinterlacing it.

[pooksahib]

Hi. I've used DGIndex to run a preview scan on the VOBs. The DVD is a film made in the 70s and the trailers are all of 70s films. During the scan the information box showed 'PAL' and a constant 'Interlaced' but, at the last minute, when the film company logo came up (2 seconds tops) it changed to 'Progressive'.

I used the arrow keys of DGIndex to scan individual frames. On frames where something was obviously in motion, there was mild combing.

Using Handbrake, I clicked 'Preview' and watched a 30 second clip. Then again with Deinterlace set to Bob. And a third time with Deinterlace set to Fast. All three previews looked fine to me, I couldn't see any difference.

What is all this telling me?

Here's a quote from www.vcodes.tv: 'Given that flat panel TVs cannot play interlaced content, if you have interlaced content it will be deinterlaced by those devices in real-time.' As I only play my videos on the lounge telly (via a WDTV Hub) why am I worrying about Handbrake filters??

manono says: 'The only reliable judge is your eyes, looking at the frames and then the fields, separated or bobbed, as already suggested.' I've looked at the frames, how do I look at the fields/separate them?

My continued thanks to you all.

[LigH.de]

Did you run DGIndex on the VOB files exactly as they were authored on the DVD (wrong), or did you extract the main movie PGC first (correct)? Most tools only work correctly with a single PGC with a single camera angle. Extracting the PGC of the main movie often already gets rid of junk trailers.

Watching a preview in full speed doesn't tell you much. Looking at 30 fps progressive or 60 fps bobbed won't look very different, except for the lower vertical resolution and some juddering. Looking at it step-by-step will reveal the temporal progress.

[jagabo]

I used the arrow keys of DGIndex to scan individual frames. On frames where something was obviously in motion, there was mild combing.

What is all this telling me?

The videos contain interlaced frames.

Here's a quote from www.vcodes.tv: 'Given that flat panel TVs cannot play interlaced content, if you have interlaced content it will be deinterlaced by those devices in real-time.' As I only play my videos on the lounge telly (via a WDTV Hub) why am I worrying about Handbrake filters??

Because the videos must be encoded and flagged properly for the TV to recognize it is interlaced.

I've looked at the frames, how do I look at the fields/separate them?

Use a bob or field separator filter. You can do it in AviSynth with Bob() or SeparateFields(). In VirtualDub you can use the Bob Doubler filter.

What remains to be seen is if the interlaced frames are 50 field per second video or if they are phase shifted 25 fps progressive film frames. That's what a bob filter will tell you.

You can also encode a short section in Handbrake at 50 fps with the bob deinterlace filter enabled. Step the resulting video frame by frame. If you see each frame twice you had out of phase PAL. If each frame is unique you had interlaced video.

[pooksahib]

Did you run DGIndex on the VOB files exactly as they were authored on the DVD (wrong), or did you extract the main movie PGC first (correct)?

I did it the wrong way... Googling for PGC extraction didn't go well. What's the best (easiest!) way?

jagabo, I'll try that 50fps trick of yours later. Right now, I gotta go to bed, been a long day.

[manono]

What's the best (easiest!) way?

To extract by PGC with the complete DVD already on the hard drive, one way is to use PGCDemux. Open the IFO for the PGC you want and you can save out the demuxed audio/video/subs, or you can choose to save as a VOB.

[LigH.de]

Usual DVD Rippers, set up to "Movie mode" (a.k.a. "IFO mode"), will check for the PGC with the longest playing time and assume this would probably be the "main movie" you want to extract and convert. That's not always the case, but in most cases it will fit.

PGCDemux can do similar things when you already ripped the whole DVD file by file. It will work from a harddisk or unprotected drive only.

In both cases, you will probably have a choice to extract either a "PGC VOB" (continuous or with a new 1 GB segmentation), or enable "stream processing" to get raw video and audio streams demultiplexed.

[pooksahib]

In Virtualdub you can use the Bob Doubler filter.

Not yet I can't. I've used PGCDemux to get the film (minus trailers) in both VOB and m2v formats. VirtualDub 1.10.4 (portable) won't load them saying "cannot decode MPEG-2 video streams". Any ideas on how to I can use VirtualDub? I don't fancy AviSynth with it's lack of GUI.

Side issue: I can easily load the Bob Doubler filter in my portable VirtualDub but it doesn't 'stick'. On next launch, no filters are listed. Am I doing something wrong or is that just the way it is?

[LigH.de]

There are so many converter GUIs based on AviSynth, you hardly need to manually edit scripts. Just VirtualDub is only an AVI editor and will always be... well, more or less: With some additional input filters, you may open MPEG-2 video in VirtualDub v1.10+; there is e.g. this Virtualdub FFMpeg Input Plugin.

And yes, VirtualDub filters have to be set up for each video, each time you open VirtualDub.

To make it clear again: The scripts to look at the fields separately are only meant to look at the video to detect whether they are interlaced at all, and in which way. To handle a present interlacing for your final copy, you probably won't keep this bobbing result, at least not in every case.

[manono]

VirtualDub 1.10.4 (portable) won't load them saying "cannot decode MPEG-2 video streams".

On the VDub page, scroll down until you see Virtualdub import plugins/filters: and there you'll find the MPEG-2 import filter.

I don't fancy AviSynth with it's lack of GUI.

If you're serious about your video encoding hobby, sooner or later you'll want to learn it. And, judging by your 'name' you sometimes work with Indian DVDs. If so, you won't be able to do decent work without it.

[pooksahib]

Good morning, guys, and thanks. LigH.de – sorry, couldn't get your plugin to work. Manono, yours worked fine. I'm British, I took my handle from a character in one of my favourite books. I'm now going to see if I can work out (as jagabo has mentioned) “if the interlaced frames are 50 field per second video or if they are phase shifted 25 fps progressive film frames”.

See you later.

[pooksahib]

I'm struggling again. The m2v file created by PGCDemux is loaded on VirtualDub. The 'bob doubler' filter is active – when I click forward frame by frame, the input monitor moves every other click, the output monitor changes with every click. That'll be due to 'bob' making the output 50fps against an input of 25fps, yes?

Jagabo said: “What remains to be seen is if the interlaced frames are 50 field per second video or if they are phase shifted 25 fps progressive film frames. That's what a bob filter will tell you.” So how do I make the call as to which it is?

[jagabo]

I'm struggling again. The m2v file created by PGCDemux is loaded on VirtualDub. The 'bob doubler' filter is active – when I click forward frame by frame, the input monitor moves every other click, the output monitor changes with every click. That'll be due to 'bob' making the output 50fps against an input of 25fps, yes?

There will always be some change with every frame with the bob doubler. Sharp horizontal edges will bob up and down by one scan line (hence the name). But watch for other motion between fields. For example, in a horizontal panning shot does the motion move with every field or does it move only every other field? If the latter, you can fix it with AviSynths TFM(). I think Handbrake's Telecide does this too.

I don't remember -- did we already establish that your source was field blended? If that's the case you will see some fields that are a blend of two different film frames (assuming it was otherwise film based). They will look like double exposures when there is motion. Those are candidates for AviSynth's SRestore(). There is no equivalent in Handbrake.

[pooksahib]

I've decided I'm not going to devote a lot of time to this. Sure, I want my (very few, to be honest) DVDs converted in as HQ as possible but turning the task into a hobby, as manono puts it, is not for me. It's all very complicated stuff and the amount of uncertanties also puts me off e.g. “And even if you do see interlacing, it still may not be interlaced (only phase-shifted fields)”.

Anyway, for the DVD in question, I've taken a clip and made 3 copies with Handbrake – no filters, bob deinterlace and default decomb. I also downloaded someone elses rip. Played all 4 on my TV and all were perfectly fine, couldn't tell the difference. So I'm keeping the rip, it'll save me a job.

But I've learned some things these last couple of days that may well come in handy at a later date. I thank you all for your help.

[pooksahib]

I've just finished experimenting on another DVD. After determining it to be PAL interlaced, I made two samples - one with no filters and one with 'decomb/bob' with fps set to 50. The latter was noticeably better so that's what I'll use from now. Thanks again for all the tips.

[hello_hello]

There's a difference between decomb/bob and deinterlace/bob, as per my earlier post. If you select a constant frame rate output at 50fps, decomb/bob will only deinterlace the frames it thinks require it, but it does miss fine combing. Deinterlace/bob will deinterlace every frame so it won't miss fine combing, but it can blur frames without combing a little.... or any progressive sections.

If a video is all or mostly interlaced I'd go with deinterlace/bob myself. If it's predominantly progressive then maybe decomb/bob, but I guess it's personal preference. The residual combing decomb/bob leaves behind annoys me, and when you have a few frames that aren't deinterlaced followed by a few that are, then some that aren't etc etc.... I find that distracting if it results in a quality difference.

[pooksahib]

Hello hello_hello and thanks. I've just tested a deinter/bob/50fps and it may just have the edge. Not much in it...