Slow motion and converting from 60p to 30p

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Level 1

6 points

Slow motion and converting from 60p to 30p

I have the option of shooting some of my videos in 720/60P on two of my cameras, while the rest of my cameras shoot only in1080/30p or 1080/60i.

Assumptions:

When FCPx retimes a 60p clip I'm assuming that it just reduces the frame rate and does not duplicate any frames. So retiming a 60p clip by 50% has the effect of making it into a 30p clip in terms of its actual frame rate. Correct?
Does changing the video quality options have any impact on this?
Now if I export my retimed clip 60p clip as a 30p mov or m4v, it won't remove every second frame as it would if I took a normal speed 60p and output it as 30p. In other words, the output of the 50% retimed 60p clip would still be 30 actual frames of data per second in a 30fps m4v file. Correct?

I'm considering doing all of my footage intended for slow motion, shot in 720/60p, then placed in a separate project for retiming.

I then create a new project and use it to merge my 1080/60i footage with the retimed 720/60p for final output to DVD. I think it's probably best to create a 720/30p file out of the 1080/60i project and work in 720 on to DVD.

I'm going through all of these gymnastics for one very awkward reason. I'm filiming fly rods and fly lines moving at fairly high speed. If I shoot this action in 1080/60i and then retime to 50%, in some frames it looks like there are two rods and two fly lines instead of one, as each field has captured the rod and line in a slightly different position. At normal speed this just looks like blur, but slowed to 50% and if the rod or line speed is high enough, then the rod or line each look like two objects. Speeds slower than 50% just look very jerky. Changing the video quality options has no effect on this problem.

Shooting with the 1080/30p camera produces better results without the two-for-one issue, but given the speed of the rod and line, 60p is a much better option, even if I have to drop down to 720.

Any errors in this thinking?

Posted on May 23, 2013 11:22 AM

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Answer 1

Rusty Rat Author

Level 1

6 points

May 23, 2013 1:09 PM in response to Rusty Rat

Tried a test in the backyard with a camera set at 720/60p, then dropped into FCPx and retimed at 50%. A master file was output and that was dropped into Compressor for output in m2v for DVD.

Just what the doctor ordered. Silky smooth slo mo, no artefacts and no two-for-one effect.

Sometimes just typing the question leads me to the answer.

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Answer 2

Rusty Rat Author

Level 1

6 points

May 23, 2013 2:53 PM in response to Rusty Rat

Results:

Test drove the entire workflow: created a 720/30p project, imported clips shot at 720/60p slowed to 50%, plus 1080/30p and 1080/60i clips into the timeline. Slowed copies of the 1080 clips to 50% also. Output a master file, then Compressored it to MEPG-2 for DVD. Not bad at all. It will do the job. The slowed 720/60p was definitely better for motion than the other two at 50%. Out of the two slowed 1080 clips, the 30p was the best.

Interesting that whether or not I see the two-for-one artefacting in the interlaced footage is dependent on the speed of the rod and the line movement. Depending on the clip, I see it either at normal speed and not at 50% speed or vice versa. Seems to be a harmonic thing going on here. Interesting problem when shooting interlaced.

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