MC MPEG Encoder questions

Frenchy wrote on 12/11/2003, 10:21 AM

System: Vegas 4.0(d)
Dell P3-600MHz
Win 98SE
384 MB RAM

In the MC MPEG-2 Encoder, there is a check box titled "Allow Field-Based motion Compensation" located here -

File-->RenderAS-->MainConcept MPEG2-->SVCD NTCS Template-->Custom-->Advanced Video tab

What Does this do?

In the SonicFoundry "MPEG Encoding Overview: Using the MainConcept MPEG-2 Plug-in, Revision 12, Dated 05.10.02", Page 19, the description is given as such:

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"Allow field base to motion compensation

Select this check box if you want to use field- and frame-based motion prediction when predicting
frames. When the check box is cleared, only frame-based motion prediction is used.

Recommended settings:
NTSC SVCD: unchecked
PAL SVCD: unchecked
NTSC DVD: unchecked
PAL DVD: unchecked

This setting should be changed only in highly specialized situations where there is a specific
reason to do so. "

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What does this "mean"?, and what is a "highly specialized situation"

My situation is this: I'm putting together a video, producing it as an SVCD, comprised of a combination of stills and DV with a music bed. In one section of DV, I've sped up the video (using cntrl-drag), and rendered it as a new DV-avi, inserting it into the main video. The scene is people loading a chairlift, and speeding it up gives a humorous effect (at least to me). The problem is, when rendered as an SVCD, because of the sped-up motion of something already moving fairly quickly, I'm getting some interlacing artifacts, and what I would describe as compression artifacts. Fine - switch on "reduce interlace flicker", and most of it goes away. But there's still some artifacts (I know I won't get rid of all, due to the relatively low bitrate nature of the SVCD format). I also tried checking this "Field-based motion compensation" box, and it seems to help a bit. Which is good, but I want to know the "what" and "why" of this switch. Are you listening MCTech?

Also, does anybody have any other suggestions to soften the artifacts from this sped-up motion?

thanks

Frenchy

Comments

Frenchy wrote on 12/12/2003, 7:42 AM

bump

I just want to try for another response, before this gets buried.

If the above post is too long to read, the question(s) is (are):

What does the checkbox "allow field-based motion compensation" do?

When should one use it?

thanks

ScottW wrote on 12/12/2003, 9:16 AM

Well, here's a guess.

With 30fps video each frame is composed of 2 fields - even and odd. Motion compensation typically deals with an entire frame which is probably fine if your source material is 30fps.

However, if some sort of pulldown was done, say you had something which was converted from 24fps to 30fps (3:2 pulldown), you're going to end up with frames in the 30fps set that are composed of 2 different frames from the 24fps source. This may cause issues for frame based compression; switching to field based compression would avoid the problems.

Like I said, just a guess.

MainConcept wrote on 12/12/2003, 1:04 PM

Frenchy,

For what you're doing this setting won't provide any help. It will simply have the encoder do motion searching on a field basis rather than a frame basis. It really is one of those settings that would only be needed in very rare cases in certain specialized settings.

Mark
MainConcept

MainConcept wrote on 12/12/2003, 1:06 PM

Regarding the artifacts you're getting in general, I just wonder if they are the limitations inherent in the SVCD format. There's only so much bitrate available, and with high-motion content the encoder can only do so much -- no matter how good it is.

Are you seeing them on a computer monitor or when playing the finished disc on a TV monitor?

Mark
MainConcept

Frenchy wrote on 12/15/2003, 8:17 AM

Thanks for the reply, Mark. I realize the limitations in the SVCD format. I am seeing them on the TV monitor, playing the SVCD. I think I got it good enough to distribute (family vid for Xmas gifts). I guess I'll have to upgrade my PC this year, and get a DVD burner. My truck is getting tired also, and needs replacing as well.

sigh

Maybe it'll rain (snow) dinero on me in the near future...

My main question still remains. In your prior post, you said

" It will simply have the encoder do motion searching on a field basis rather than a frame basis. It really is one of those settings that would only be needed in very rare cases in certain specialized settings."

What "are" the "specialized" circumstances where field-based motion compensation would help? Curiously, in this situation, on this clip, it did seem to help.

Also, does anyone think a little motion blur and/or supersampling wuold help reduce the "appearance" of the artifacts? I use it regularly on slo-mo events. Just wondering if it would help of fast-mo as well. With what I did, I got it to look good enough to give out (And it was too many late nights in a row - I needed SOME sleep...)

thanks

Frenchy

johnmeyer wrote on 12/15/2003, 1:29 PM

If you are encoding to SVCD from a source that was originall film, you get MUCH better results doing inverse telecine first. TMPGEnc is the only way I know to do this. If you are encoding from NTSC DV source, you may want to apply a little blur. Again, TMPGEnc permits this as part of the encoding process.

I generally prefer the Vegas for all MPEG-2 encoding, but for the few SVCDs I still occasionally do, I think you can get better results in TMPGEnc. I can send you the template I use, if you're interested.

Frenchy wrote on 12/15/2003, 4:24 PM

Hi John:

My source files are a mix of NTSC DV and fairly hi-res digital stills to allow for pan and zoom. I tried TMPG in the past, and I was happy with it, but I've been wanting to keep it all inside of Vegas for the sake of simplicity. I'm comfortable with the embedded MC encoder now, and from what I remember, TMPG would freeze up my PC occasionally. It also seemed that the *slight* quality gain was not worth the additional effort. Also (to my eye) he MC encoder in V4 is significantly improved over the VV3 version.

Like I posted at the top, there are only a couple of sections that showed some less than desirable artifacts - Those that had high motion originally, and I applied a velocity envelope to it which exacerbates the situation.

In TMPG, can you apply "a little blur" to select parts of the vid, or does it get applied to the whole thing? As you know, in Vegas you can apply a little blur at the event level so that it doesn't unnecessarily increase the overall encoding time

I would like to try your template - send it to me at Phill AT krcl DOT org

Thanks

Phil

johnmeyer wrote on 12/15/2003, 6:45 PM

I have sent the template.