Problems with Velocity Envelopes and Looped Frames

[TimStannard]

I'm sure I used to do this sort of thing no problem. Take a quick look at the video here (if you want) and note the use of freeze frame.

My original plan was to ramp the speed down using velocity envelopes either to slo-mo or to a stop, then ramp it up again.

However I experienced problems with the image flickering. I've used this technique before, but not for a while and dont remember experienceing this. The flickering was present in preview and rendered video (incidentally this is all standard def avi and the problems were present on rendered avi and mpg).

So, I did away with the slowing down idea and went to a still, using the time-honoured method of selecting a single frame as a subclip, and looping that.

I was delighted to discover that for these particular clips, going to a sudden stop seemd to work just as well as slowing down.

However i was not delighted to discover that, whilst the still image was great in the preview screen, it flickered in the rendered version (both avi and mpeg2).

So I replaced the looped frames with jpegs created from the preview window "snapshot" and all looked well.

I was able to work around for this video, but i'm rather concerned that something I used to do regularly (but possibly not with VP11) doesn't seeem to work now. I'll have to experiment with new projects.

[Midnight Blue]

Just a wild guess, as I have no idea really, could it be a shutter speed on the camera issue or is it definitely a software thing ?

[TimStannard]

Just a wild guess, as I have no idea really, could it be a shutter speed on the camera issue or is it definitely a software thing ?

Well, it's certainly true that when I've done this before the shutter speed has been 1/50 and on this shoot I used 1/180. I don't see why it should matter as all this means is that the shutter is open for 1/180th sec, 50 times per second, instead of being open for 1/50th sec 50 times per second, but it's worth persuing. I'll see if I can shoot some other footage and 1/50 and 1/180 and try this out.

[Midnight Blue]

I wouldn't waste too much time on my wild uneducated guess.

My theory was something on the order of frame rate/shutter speed ratio. I can't remember what exactly or where I read this but it was something about setting shutter speed in multiples of 25 (for PAL cameras) because of the frame rate but as I say it's probably not related to your issue.

[Z Cheema]

When doing stills with the velocity envelope it does sometimes happen you get the flicker because of the fact it is an interlace image.
You need to right click and choose properties and then the force option (cannot remember the actual name)

Best use the still option by capturing a still

In DVD-A there is a an option to reduce interlace flicker, it is on the right pane.

[TimStannard]

Thanks, Z. Sadly not the solution (in this case anyway). I haven't tried DVDA as this is for the web.
I think you're referring to force resample, and there is also a switch for the event for reduce interlace flicker. Force resample seems to have no effect and reduce flicker does work but has other undesirable side effects (ghosting)

But hold fire. The AVI I just uploaded to demonstrate the problem does not have the problem on YouTube (although it is displaying in 4:3!)

To be continued ...

[Z Cheema]

When rendering out try setting the template to Progressive as it is for web