Quartz Crystal : Low levels of motion blur

psonice's picture

This probably isn't a common case, but I have a few frame-rate sensitive compositions (feedback, the 'rainbow smoke' type effects etc.) that I'd like to render.

The catch: I want to render at 30fps (no problem) but with a 60fps 'composition frame rate' (problem). Really, all I need is a 2x motion blur to render 2 frames per output frame, but 16 is the minimum. (16x motion blur + 30fps = FAST movement). Any way around that issue?

Also, seeing as the movement is much faster (in theory, motion blur should just make it brighter in the last test I did), is motion blur somehow messing with the clock speed? Or is it using the system clock (i used a system time patch to add "different each timeness") and just rendering slower than realtime, so it ends up fast?

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cwright's picture
Re: Quartz Crystal : Low levels of motion blur

2x motion blur is possible via the command-line interface. however, it might not look pretty (the ui makes 16 a minimum because fewer than that tends to look bad for most composition -- ghosts instead of blur, etc etc).

system time doesn't use the QC clock at all, it uses the system's clock (surprise! ;), so it'll run much faster in Quartz Crystal (because it takes much longer than real time, on average).

Alternatively, you can hook the QuartzCrystal motion blur input, and modify your frame-rate-dependent-effect to only operate every N frames (where N = 8 at 16x motion blur -- that'll work, but it'll waste a lot of time re-rendering the same thing 8 times...)

gtoledo3's picture
Re: Quartz Crystal : Low levels of motion blur

My feedback stuff looks pretty darn similar (identical in 99% of cases) in render to Quartz Crystal... though I'm not exactly "mr. subtle" with what my qtz's look like. Whispy delicate clouds with sparse background like you speak of... especially if drawn slow could be a problem...

Have you thought about rendering at 60fps, and then converting to 30fps with something like mpeg streamclip, or imovie? Does the feedback look correct when you render at 60fps, but not at 30fps... or does it look incorrect with both?

psonice's picture
Re: Quartz Crystal : Low levels of motion blur

It'll depend on how you're doing the feedback. If you're doing the 'zoom blur' type effects, it's totally frame rate dependent and your results will vary massively depending on how you render.

E.g. if you do a zoom feedback where you render something, then make it 10% bigger and add it to the background, that happens each frame. As the comp plays you get a nice cool zooming feedback effect. If you render in crystal with 16x motion blur, what happens is that it makes the background 10% bigger 16 times per frame - i.e. it's now getting 160% (actually much more in practice) bigger - it's the difference between a nice smooth effect and stuff flashing across the screen faster than you can see it :)

For the rainbow smoke type stuff, I'm rendering a lot of stuff with additive blending. With 16x motion blur, that means it adds 16x more stuff per frame, so the image should end up 16x brighter. I was using system time though, which totally messed up the speed anyway.

Rendering at 60fps and converting back is a good idea, but I can't be arsed :) Way too busy lately. I'll do some captures later though so you can see what these things look like with 32bit rendering.

Chris: thanks, I'll either stick to 30fps or try 2x motion blur from the command line. This is a rare case where that will work well :)

gtoledo3's picture
Re: Quartz Crystal : Low levels of motion blur

Hmmm, that's an interesting breakdown on that. Thanks! Yeah, I forgot that you do tend to do stuff where the filter itself gets fedback... which is quite cool! However, I do throw that in a lot as well... I'm going to have to take note of the 10% bigger thing, b/c it hasn't cropped up for me with my setups.

When I want the most stunning visual results with Quartz Crystal (which I'm actually not shooting for too often)... I've done png, 60fps, 1280x720 HD with whatever the max antialiasing I can do without the offscreen render failing. However, that will make a massive file... which I will subsequently downsample(hmm, not sure if that's the right word, but it would apply in the realm of audio!), to H264 30fps, and whatever the target size is.

For whatever reasons, it looks better to me to render at a bigger size and png, then actually reduce size after the fact... though I don't usually go through the trouble because it is sort of splitting hairs, and for minimal gain for the time involved. I haven't messed with 1920x1080 too much.

I haven't done that in a bit, and I didn't do real double blind tests or anything, so even I take this observation of my own with a grain of salt. I wouldn't be surprised if I thought something different for rendering on another occasion... I DEFINITELY had best results rendering to 15fps for one thing, because it gave it a charming old school animation look. It's all situation dependent I think.