Getting slow motion in Long GOP - advice please
 

Hi all,

I would like to try and get some slow motion footage of bats inflight using Long GOP rather than I-Frame only. I have done some testing with 720 60p/50p I-Frame only at 160Mb/s and I am still not sure about the results. It looks as if there is some serious CA that isn’t there when I shoot with the same lenses in Long GOP. I am mot sure this makes sense and it can be that I am doing something wrong when processing.

Will shooting 720 50p/60p Long GOP at 160 Mb/s then converting to 25 fps do the trick?
Can anyone please describe the right workflow in FCP ?

Thanks in advance,

Ofer Levy Photography

Yes that will work, but converting is not the right word, rather conforming. In FCP you'd use Cinema Tools, but it only does it with I Frame so you'd need to transcode the footage first to ProRes HQ first. This is why it'd be better to shoot I Frame in the first place!
If anyone else knows a different way to conform to 25P, with a different program maybe, I'd be interested to hear it.
Good luck with the shoot Ofer.
Steve

Dear Ofer,

While this may not directly answer you question, I am submitting this in case it helps.

One of the myths about Long-GOP is that all of the detail in each frame is not there, the myth is that the detail is only in the I-Frames and not in the other frames.

This is simply not true.

Once your footage gets into your NLE, all of the frames are recreated and the NLE deals with each individual frame.

In my opinion and based on tests that I have seen, 100 Mbps Long-GOP due to its higher codec efficiency can preserve more detail than 100 Mbps I-Frame Only (Intraframe) at 160 Mbps.

Our 140 Mbps and 160 Mbps Long-GOP provide even more insurance that you will preserve the detail in your original images.

Ofer, if you're capturing at 60fps then you'll want to conform that footage to a lower framerate in order for it to playback in slow motion. Conforming doesn't actually change the picture data in the file, only the metadata that determines the rate of playback. You can't do this in Final Cut, not as far as I know.

If you have Final Cut Studio, you can do this in Cinema Tools, which is how I recommend you do it.

I've done it a few times but not since I got the XDR. I can run through the workflow real quick today if you like. I've got some spare time.

Thanks Dan and Aaron.
Aaron, yes please give it a try and let me know how to do it. I am new to FCP and it is not that simple for me to get it right with the limited knowledge I got.
I do have Cinema Tools.
Since I live in a PAL country - I am not sure whether I can shoot 720 60p which is only offered to NTSC countries in my camera (EX3). I would prefer to use it over 720 50p for the extra frames which will give me slower slow motion.
Thanks mate,
Cheers,
Ofer

Yes, you are correct. The 60p will give you slower motion, which is probably better for what you're trying to do. Just make sure you conform to the correct final playback rate for your project (probably 25fps).

I just shot my 60p footage a few moments ago. Going to go through the steps to make it slow motion right now. Will post back in a few minutes.

Dear Ofer,

If you camera can shoot in 60, then we can record in 60.

Please note that to get 60p, you have to use 720p60, 1.485 Gbps HD-SDI does not support 1080p60.

Ok, all done. It was actually pretty easy. The only gotcha is that Cinema tools doesn't support long GOP, which is OK because I have been doing all my finishing in either uncompressed or ProRes.

Here's how I made the slow motion clip.

* Set my camera to 720p60
* Recorded some footage
* Copied the clip from the flash card to my computer
* Put the clip into a timeline in FCP (after trimming the head and tail in the viewer)
* Export the sequence to ProRes or Uncompressed if you like
* Right click on the exported clip in the Finder and choose Open with Cinema Tools
* In Cinema Tools, click on Clip -> Conform and set the frame rate

That's it. You're done. Takes less than half a second for the conform to finish. You don't have to save anything, just exit Cinema Tools. The clip will now playback in slow motion.

Let me know if this helps or if you have any questions.

Thanks so much Aaron! I really appreciate your effort!
Will give it a go later today and will report. (Have to take my baby to the daycare...(-: )

Cheers,
Ofer

Hi Dan, my EX3 can only do 720 60p so I guess there is no problem.
Thanks,

Ofer

here's my footage, compressed to H.264

http://www.vjaswift.com/archive/slomo.zip

46 seconds of 60p footage, conformed to 23.98 and is now 1:54. i pumped up the colors a bit since I was bored.

it's footage of me walking through the complex with the camera hanging slack armed at my side. lens is set to near infinity, stopped down to about f/4. XDR was set to 100MB long GOP.

That's exactly what I said! No harm having it confirmed though!

Couple of points about uncompressed. When the editor did the transcode from my PDW700 we noticed that the quality was definitely better going to uncompressed than to ProRes, though still not as good as the original. Also, the files are MASSIVE! Ofer, I still think it's hugely worthwhile capturing in I Frame to begin with, saving the very lengthy and qulaity-dropping trancoding step, just leaving the conform which as Aaron is really quick.

If there are artefacts on the I Frame footage from the XDR that aren't there on the Long GOP footage that needs investigating as it doesn't seem to make much sense.

Steve

Although Intraframe, I'm not sure CinemaTools will want conform it being an MPG-2.
Short (very short) GOP, but GOP.
Rafael

Whatever time base you shoot, once conformed to 720p25, the file is fully PAL-like legal.
Shoot p60 when you need slower motion.
p50 makes a lot of sense if you ever need to play the movie at normal speed, and this is likely to happens some times.
Cheers,
rafael

Someone should test and see if Cinema Tools will conform the Intraframe MPEG2. Methinks it won't.