Are you editing in a 50p project or a 25p project? You should edit in 25p and conform the media to slow it down.
Slow motion quality depends almost entirely on what's being slowed and how it was shot, especially with optical flow. Moving camera can making very weird things happen. Can you post a bit somewhere?
Optical Flow in FCPx is the best algorithm availble IMO -- IN OPTIMUM CASES... ;-)
If you have motion blur in your image -- Optical flow is your wirst enemy.
Attributes of Slow Downers"
Normal Quality will NOT alter image frames... If i.e. you have a 25p film, slowing it down to 50% will have FCPx playback each frame twice - making it look slower but choppy
Frame Blending... in same scenario as above will blend (mix) the two frames - creating a "third frame" based on the blended result. Which most of the times looks weird.
Optical Flow = Will physically try to figure out what the missing frames "should" look like... And it does a fantastic result as long as motion blur is not happening... If motion blur is heavily present in the footage you need not bother even trying.
Optical Flow in FCPx is often referred to as "Pixel Motion" or Vector Interpolation on other apps.
If you REALLY need to apply a "slowdowner" with pixel motion / optical flow to a clip with heavy motion blur.. You will need to rotoscope it. I did this once on an impossible shot and it took me a whole day rountripping between FCPx, Mocha Pro, AE & Photoshop. 4 Apps + 12 hours... Next time I'll shoot with phantom instead. But the shot was worth it.
Hope this helps
Tom, I am editing in 50, and was trying to slow down birds flying, fast movements for small birds but just leaving the trees. And Studio Engineer you give me a detailed instruction, so it seems that the process is not so simple as thought. Just "rotoscope" I do not fully understand that term. (maybe my bad english)
Thank you both.
Rotoscoping is the art of making i.e. a Bird flying accross the sky, stand alone... What I mean is that it will in this case leave you with two layers of movies (Or two movies)
Imagine duplicating the clip I am describing above, twice... One is lying in the main timeline and its duplicate is lying directly above it. Both clips identical.
Now, we'll "mask out" the background of the above clip. So that if we solo the that clip you would see all black(Depending on your movie background (The black is actually transparency) and then the bird flying accross the screen. In the clip below we'd "Mask out" the bird and replace its place in the film with content from it surroundings (Much like clone stamping in photoshop) ... In the end and if the clip above (with the bird only) had a carefully created mask, we'll have the bird on one layer and the background on the other.....
(IF it was a steady shot thus not panning, craning or sliding) we could create a clean-plate of the background and just have that sitting as a still image while the bird is flying)
Anyway, now we can apply optical flow to the bird and if the mask is tight, the most motion blur will have vanished and our result is great looking... Now there might be a few places with optical flow artifacts... But then we'd just mask those out as well ;-)
This level of masking (Rotoscoping) cannot be done in FCPx -- you would use After Effects for such or motion... However, AE is much greater for such (in my opinion at least ;-)))
In above case, I would problably wind up with MUCH more than 2 layers of video. More like 50... The clip I wrote about in my earlier post had about 500 ;-))))
Rotoscoping is vast and great... And it is more of an art than a technique. Basic rotoscoping would be to apply a mask to a man's sweater and keyframe it to fit the motion... Then alter its hue or tag a big sign saying "Rotoscope Me" on his chest..
Possibilities are endless ;-)))
Mocha Pro which is a planer tracker is the best tool on the planet to help one automate the "Masking & Tracking" & it comes free in special version with After Effects.
hope this helps ;-)