40% Slow Motion / Correct Shutter Speed?

[kmcgrath]

Barry recommends (in The DVX Book) using shutter speed of 1/120 sec for 40% slow motion (shoot 60i, use 24p timeline). Is this shutter speed of 1/120 sec essential, or could I go as low as 1/60 sec with similar results (except the higher level of motion smear and 2X exposure difference of 1/60 sec vs 1/120 sec)? Thanks much!!

[Barry_Green]

The 1/120 recommendation is based around the idea of keeping similar motion blur to the 24p footage. You are certainly free to change the shutter speed to whatever you want, as long as you keep in mind that it will change the motion blur. 1/60th would deliver similar motion blur as if you shot 24p at 1/24th.

[kmcgrath]

Thanks Barry. I tried both your 40% and 50% slow motion methods. I think I like the look of the 40% better (shoot 60i, 24p timeline, velocity envelope 40%) due to the absence of interlace artifacts. With the 50% slow motion method (shoot 60i, 60i timeline, velocity envelope 50%) I see some interlace artifacts. Does that sound right? I was thinking I wouldn't see the artifacts because it would be like viewing 60 progressive "frames" (e.g., fields) during the course of 2 sec??

[Chance White]

Is there a way to get good slo mo out of 24p footage shot at 120 shutter? Maybe just 80%?

Or will this not work?

[kmcgrath]

I don't think so. You could shoot 30p and on a 24p timeline you would get 80%, full resolution progressive.

[blckhawk542]

speaking of slow motion in Vegas...i got this problem...my camera..its not the greatest camrea in the world...it shoots at the standard 29.970i ...now when i want to make something slow motion...i see a lot of flickers and stuff on the tv monitor..so i clicked Force Resample and Reduce Interlaceflicker..but it didnt do anything...am i doing something wrong?

[jaegersing]

Check the project setting is for NTSC, Lower Field first, and that your clip properties are the same. Also in Project settings, try Deinterlace Method set to Interpolate. This usually produces pretty good slo-mo without any Reduce Deinterlace Flicker or Force resample applied.

[blckhawk542]

it is for NTSC..and it it matches the project settings of Lower field first...which i have no clue what it means...but ye..all the clips are the same in that retrospect...but wat would the Deinterlace Method do? ive tried using that before..and i got wavy edges on my video whenever something moved..wat does the Interpolate do? i jus dont get ne of this technical stuff....aahh

[jaegersing]

The 29.97 video is interlaced, with Upper Field alternating with Lower Field. When you apply slo-mo, Vegas has to deinterlace the video in order to slow down the frame rate. If the field settings are not correct, you will get a kind of 2 steps forward one step back jerkiness on the slo-mo clips.

The deinterlace method is either blend fields or interpolate fields, and this is used to create the extra frames that are needed when the video is slowed down. I'm not sure exactly what the difference is, but I find Interpolate works best for most cases. Blend tends to produce a softer image whereas Interpolate seems to remain sharper. I have heard others say they prefer Blend, so there must be some personal taste factor involved too.

I'm not sure about the wavy edges on your video. Unless you apply slo-mo or some other effect that requires the video to be deinterlaced, the Deinterlace Method should not actually affect anything. Did you get the wavy edges on a straight playback of the clip?

[jaegersing]

speaking of slow motion in Vegas...i got this problem...my camera..its not the greatest camrea in the world...it shoots at the standard 29.970i ...now when i want to make something slow motion...i see a lot of flickers and stuff on the tv monitor..so i clicked Force Resample and Reduce Interlaceflicker..but it didnt do anything...am i doing something wrong?

Just had another thought about this. How are you sending the video to the TV monitor? If it is from inside Vegas, you would need to set the Preview quality to better than "Preview", otherwise you will not see any effect of the deinterlacing that Vegas will do when you carry out the final render.

You could try rendering a short section of the flickery bit, and then preview the rendered clip (via 1394) at Best quality. This is really the only way within Vegas to know what the final output is going to look like.

[Barry_Green]

The deinterlace method is either blend fields or interpolate fields, and this is used to create the extra frames that are needed when the video is slowed down. I'm not sure exactly what the difference is, but I find Interpolate works best for most cases. Blend tends to produce a softer image whereas Interpolate seems to remain sharper. I have heard others say they prefer Blend, so there must be some personal taste factor involved too.
"Blend" merges the fields together to create a new field -- the results of which would result, likely, in smoother motion but lower resolution. It blends field one with field two.

Interpolate will discard one field entirely, and make a new frame from just the remaining field, interpolating between its lines to create a new field. For the 60i->24p slow-mo effect, that's the way you want it. You want to turn each field into a full frame, and "interpolate" uses only one field to do so, whereas "blend" will just confuse the issue and result in interlace artifacts. (which may account for the report of "wavy edges" on the video).

Regardless of which way you go, be sure to choose "best" render quality. 60i to 24p using 40% speed, "interpolate" and "best" results in the best, most filmlike slow motion I've been able to create from DVX footage.

[jaegersing]

Thanks, Barry, for the explanation.

Richard Hunter

[kmcgrath]

Also, make sure the default "smart resample" is checked in the clip properties (so that extra frames are generated so the frame rate matches the project frame rate, resulting in apparent smoother motion; I think this would especially apply to a 50% slo mo 60i > 60i as Barry describes in the DVX Book).

But, what is the difference between "smart resample" and "force resample" in terms of the actual number of frames that are generated by the resampling? Any way to know how many new frames are generated in "force resample"?

[Barry_Green]

No difference in the number of frames. The only difference is that "smart resample" resamples only when it thinks it needs to, whereas "force resample" forces it to resample every time. If resampling happens, it'll be the same # of frames.

[kmcgrath]

Thanks Barry. Can I ask one more question? If you are in a 60i timeline, but choose "progressive" in the field order box (under project properties), does this mean that the odd and even fields are combined into a single progressive frame when played back (even though I cannot reconcile how this could occur if viewed on NTSC monitor). This question assumes that "none" is checked in the "deinterlace method" of project properties.
Thanks much.
Ken McGrath

[Barry_Green]

Haven't tried that. Presumably there's going to be some difficulty reconciling the two!

[David Jimerson]

Tried it. Rendered it. No interlace artifacts, so it's "progressive," I guess. Didn't do much for resolution, though.

[kmcgrath]

I still see interlace artifacts when I switch to "none" in field order, but if I then set deinterlace method to "interpolate", then I do not see the artifacts (presumably because I am seeing a single field progressively). I would have thought that just setting deinterlace method to "interpolate" would produce this result, but then I still see what appears to be interlace artifacts.