SVCD & Interlaced or Hybrid streams

[Pko]

Is there any reason to NOT to encode in interlaced mode to SVCD when the source is interlaced? Is ever necessary to deinterlace when doing SVCD? and what if the stream is Hybrid, that is, NTSC + FILM? I have posted a thread about this in Avisynth forum, http://rilanparty.com/vbb/showthread.php?s=&threadid=21904

[Boulder]

I have to deinterlace my captured AVIs every time. I've tried different field orders with no luck. There are no combing artifacts in the stream when I've used interlaced mode but the visual quality is better. This just bugs me because of the extra time it consumes.

[Pko]

Well, I do not know with captured streams, but I can asure you that with interlaced DVDs, compressing to an interlaced MPEG2 SVCD-standard stream looks GREAT both in WinDVD and in my stand alone player: very good quality, perfect smooth movement.

When I tried it with TMPGEnc in the past, the results were awful, but with CCE (2.5) they are wonderful. But I see that people still deinterlaces NTSC and Hybrid streams (of course, FILM streams should allways be IVTC'd since that gives enormous benefits). I do not know if they do that because of ignorance or from a "deinterlacing tradition" coming from MPEG-1, DivX or TMPGEnc origings, or if they do that because there is some problems in certain playback devices.

I can asure you, if you deinterlace (not IVTC) a FILM stream, it will take much more time to compress, the quality will be worst and the movement jerky; if you deinterlace a NTSC stream, it will take much more time to compress and the quality will be worst. If you force IVTC in a non-FILM NTSC stream, it will take much more time to compress, the quality will be bad (sometimes VERY bad) and the movement will be jerky.

So, with a hybrid stream, I think that treating it like pure interlaced is the best solutions; the NTSC parts will be compressed as they should, and the FILM parts will be compressed OK although some frames (the ones that get duplicated in the telecine process) will be compressed twice and so you are compressing redundant information, but that is no so bad in practice comparing since the higher framerate will somewhat compensate that each frame has slightly (25%) lower bitrate (they will stay on screen less time so the artifacts will be less noticeable).

Of course, the ideal solution is to IVTC the FILM parts and compress like interlaced only the NTSC parts, but I think that that is not possible with the existing tools right now...

[Boulder]

Well, we've got PAL here in Finland so I don't have to worry about NTSC and Film;)

If I convert a DVD to SVCD, I never use any deinterlacing for the reasons you stated. I'll just check the stream with Bitrate Viewer and select either progressive frames or not.

[ThePanda]

Originally posted by Pko
compressing to an interlaced MPEG2 SVCD-standard stream looks GREAT both in WinDVD and in my stand alone player

How do you do this? Can DVD2SVCD do it or do you need a different encoding tool to encode it as interlaced? Also, will temporal smoother mess up the interlacing or the rest of the picture?

[Pko]

Originally posted by ThePanda

How do you do this? Can DVD2SVCD do it or do you need a different encoding tool to encode it as interlaced? Also, will temporal smoother mess up the interlacing or the rest of the picture?

Is really simple... if the original is interlaced, in CCE you uncheck the option "progressive". Also is advisable to uncheck the "zig zag" option since I believe it gives good results only with progressive frames.

I do not know if DVD2SVCD does this (encode as interlaced) or not, I made that question in DVD2SVCD advanced forum but no answers whatsoever.

[Boulder]

You can choose the progressive frames option in DVD2SVCD as well along with the other important options in CCE.

[ThePanda]

Does anyone know of a version of temporal smoother for avisynth that allows you to specify interlaced? Or will the normal one not mess up the picture if you want to leave it as interlaced?

[Pko]

Originally posted by Boulder
You can choose the progressive frames option in DVD2SVCD as well along with the other important options in CCE.

It is possible to detect if the source is interlaced or not, and if it is FILM or Hybrid... Do you now what does DVD2SVCD do by default in that different situations?

I think it usually chooses to deinterlace, but IMHO it is a bad option since it takes time and gives poorer results. And there is the very important case of hybrid streams, I think that there the ONLY solution that gives reasonably good results both in quality and in smoothness of movement is to encode as interlaced, but if the % of NTSC is low enough then the best option is to do IVTC.

Since I usually do it manually and not with DVD2SVCD I am not sure of what DVD2SVCD does and also if what I do is the best solution

[Pko]

Originally posted by ThePanda
Does anyone know of a version of temporal smoother for avisynth that allows you to specify interlaced? Or will the normal one not mess up the picture if you want to leave it as interlaced?

I do not know nor use temporal smoother, but for what I have read, I think that it will not work very well... if it smooths only in the temporal domain, it should work OK, but if it also does some spatial smoothing (if it includes lines under or above the one being smoothed) it will find the combing and try to "smooth" it with awful results.

Perhaps you could separate the fields, use temporal smoother and then weave them again... something like

[read source]
SeparateFields()
[do smoothing and other stuff]
Weave()
[rest of script]

Well, with that you are smoothing each field with the other field in the same frame, so you are in fact doing some spatial smoothing at the same time since each field have a vertical "distance" of one scanline...

SeparateFields() makes a stream that has half the vertical resolution and double the framerate than the original; an interlaced stream of 720x576@25fps (D1 PAL) gets converted to 720x288@50fps.

Weave() does the opposite, takes the double-framerate, half-resolution stream and gives an interlaced one with the original framerate and resolution.

Of course, all this is just in theory, I suggest you to make some tests and of course do not forget to give here your feedback!

[ulfschack]

@Pko

In theory as well as in practice my friend :)

I've been using this method since half a year back. I first got the suggestion from the very competent forum dweller MB1. I know it works with temporalsmoother (inherent in some of the versions of the mpeg2dec.dll) but I still think that maybe it's not that obvious why it should.

Consider a 50 Fps stream and you're telling the filter to go N steps backwards/forwards and filter out any noise, the algorythm would then compare frames that are shifted one field up or down since they're meant to be interlaced, right? So a grain of unwanted noise (1 pixel big) would only be present in lets say odd frames (if the noise lasts for more than two frames, which I doubt is noise). I ask myself how this affects the algorythm. Maybe this way stuff that isn't noise gets filtered out anyways to a larger extent than would it have been in a progressive video. And maybe I'm just full of it.

Any intelligent (a welcome change :) ) views on this?

cheers

[ThePanda]

Yeah I was thinking that too, that it is shifted from one frame to the next, so it seems like it would blur it back and forth from frame to frame. But I don't know, I think I might just leave out the temporal smoother.
How about spatial smoother? Doesn't that have an interlaced mode? I guess that kind of ruins the picture too but maybe it would improve compression enough to compensate and would not look any different on a tv

[ulfschack]

Sorry Pko about the repetition of what you'd allready said. I must have skipped over the part where you mentioned the one scanline offset. And yes, your probably right about some spatial smoothing effect with a temporal filter on separtated frames. This actually calls for some subjective testing.

[Boulder]

@Pko: Sorry, I've been away for a while.. I don't know what DVD2SVCD does by default. However, I think that I've been very lucky as all the conversion I've done with it have been perfect (I've converted several NTSC and PAL DVDs). I've not chosen any deinterlace options as it's recommended not to deinterlace. I've not done any DVD->SVCD conversions manually so I don't know how the sources must be handled. I've had to deinterlace all my VHS captures as the result has been crappy if I haven't used Decomb (the subtitles are flickering badly!)