How best to reduce framerate by 2

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MatthiasHoeller

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How best to reduce framerate by 2

PostSat Nov 09, 2019 6:23 am

Hi,

I just finished editing a scuba diving movie and during export, I discovered that the framerate was 59,97 fps (probably due to the media which are from a GoPro mainly).

What would be the best way to get a final export with only about 24 or 30 fps? The file size is huge at the moment...

In the delivery page / export dialog, the frame rate is locked to 59.97, the frame rate drop down menu contains no other options.

I am not very experienced so I learned only now that the frame rate of a project is not changeable after starting to edit.

Please help - what do I do? I am open to all possibilities.. is there maybe a free/good and above all "easy to use" video converter to convert the final product to a lower frame rate maybe? (I'm running Windows)

Or is there a hack to trick Davinci into doing what I want?

Thanks in advance, I'm quite desperate right now...
Matt
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Uli Plank

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Re: How best to reduce framerate by 2

PostSat Nov 09, 2019 7:38 am

The perfect solution would be to redo the whole edit in a timeline with the correct frame rate. Yikes!

The quick and dirty one would be exporting the whole project as it is (if it's final) into a mezzanine codec like DNxHD/HR. Then make a new project with the proper frame rate, slap the exported result into the timeline and hope it doesn't look too bad with optical flow enabled if you need 24 fps.

If you aim for 30, you should rather try to set the exported clip to exactly 60 fps in its clip attributes, put it in a 30 fps timeline and use "next frame". Much faster.

Is your result meant to be for broadcast or for cinema, since you mention both 24 and 30 fps?
Broadcast would be 29,97 BTW.
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Michael_Andreas

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Re: How best to reduce framerate by 2

PostSat Nov 09, 2019 1:47 pm

If your goal is to reduce filesize, reducing frame-rate by a factor of 2 with h.264 or h.265 will not result in a 2x filesize reduction. What codecs are you exporting in? What is your delivery channel? (Cinema/YouTube/other)
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Marc Wielage

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Re: How best to reduce framerate by 2

PostSun Nov 10, 2019 5:11 am

The motion artifacts will be terrible (and noticeable) going to 24.00fps.

You can go to 29.97 from 59.94 pretty easily, and I don't think it will look too bad. I didn't know 59.97 was a frame rate, but you can try it and see what happens. 60fps is a frame rate, and 59.94fps and (59.94i) are industry standards to a point. Do a test and see what happens.

If you're trying to show this at a festival, 30.00fps is an acceptable DCP delivery format for newer projectors and servers. I would bet online delivery will most likely require 29.97, which is pretty standard for broadcast. (Some want 1080 59.94i or even 720p, so there's a bit of "it depends" here.)
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MatthiasHoeller

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Re: How best to reduce framerate by 2

PostSun Nov 10, 2019 8:50 am

Uli Plank wrote:The quick and dirty one would be exporting the whole project as it is (if it's final) into a mezzanine codec like DNxHD/HR. Then make a new project with the proper frame rate, slap the exported result into the timeline and hope it doesn't look too bad with optical flow enabled if you need 24 fps.

If you aim for 30, you should rather try to set the exported clip to exactly 60 fps in its clip attributes, put it in a 30 fps timeline and use "next frame". Much faster.


First of all, thanks very much for the detailed explanation. I tried to do exactly as you instructed, however I don't know what you mean with "next frame", i.e. couldn't find an option with that name.

I wasn't precise enough in my initial post. My current timeline has 59.94 fps, so I did what you recommended and selected 29.97 for the "new" timeline, as to maintain an exact factor of two between the two versions.

I selected DNxHR as mezzanine codec with an MXF op1a as container. I am new to this and decided for these after a brief google search - was it a good choice?

I am currently rendering the final result so can't tell yet the differences in file size or quality :D

Thanks again!
Matt
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Uli Plank

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Re: How best to reduce framerate by 2

PostSun Nov 10, 2019 12:00 pm

Bildschirmfoto 2019-11-10 um 12.52.25.png
Bildschirmfoto 2019-11-10 um 12.52.25.png (40.81 KiB) Viewed 267 times


Sorry, working with too many video programs. In Resolve, it's called "Nearest" and it's under "Frame Interpolation". If your quality is insufficient, play with the other options. Optical Flow will be slow, though.
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CodeTech

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Re: How best to reduce framerate by 2

PostSun Nov 10, 2019 12:13 pm

In future, you might want to keep Handbrake at the ready. It's a really simple transcoder, and even uses NVENC and NVDEC, so can do what you're asking at something like 300fps.
It's free.
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Andrew Kolakowski

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Re: How best to reduce framerate by 2

PostSun Nov 10, 2019 12:46 pm

MatthiasHoeller wrote:
Uli Plank wrote:The quick and dirty one would be exporting the whole project as it is (if it's final) into a mezzanine codec like DNxHD/HR. Then make a new project with the proper frame rate, slap the exported result into the timeline and hope it doesn't look too bad with optical flow enabled if you need 24 fps.

If you aim for 30, you should rather try to set the exported clip to exactly 60 fps in its clip attributes, put it in a 30 fps timeline and use "next frame". Much faster.


First of all, thanks very much for the detailed explanation. I tried to do exactly as you instructed, however I don't know what you mean with "next frame", i.e. couldn't find an option with that name.

I wasn't precise enough in my initial post. My current timeline has 59.94 fps, so I did what you recommended and selected 29.97 for the "new" timeline, as to maintain an exact factor of two between the two versions.

I selected DNxHR as mezzanine codec with an MXF op1a as container. I am new to this and decided for these after a brief google search - was it a good choice?

I am currently rendering the final result so can't tell yet the differences in file size or quality :D

Thanks again!
Matt



For halving the fps don't use Optical Flow as its potential advantages will be overshadowed by possible artefacts.
Simply use Nearest which will end up with Resolve dropping every frame.

Simply create new Timeline at 29.97 and drop original timeline to it and export.
This will give you exactly same end result without an intermediate file.
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Jim Simon

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Re: How best to reduce framerate by 2

PostSun Nov 10, 2019 3:40 pm

MatthiasHoeller wrote:The file size is huge at the moment...


File size = bitrate x duration.

Parameters like resolution and frame rate have no bearing on file size. If you want a smaller file, you need to reduce the bitrate, shorten the program, or both.
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Marc Wielage

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 1:38 am

Andrew Kolakowski wrote:For halving the fps don't use Optical Flow as its potential advantages will be overshadowed by possible artifacts. Simply use Nearest which will end up with Resolve dropping every frame.

I think this makes sense. Though I would consider Speed Warp under some circumstances (including the potential 29.97 -> 24.00 conversion). Of course, do a test for a minute or so first and make your decision based on the results of the test.
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Andrew Kolakowski

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 7:21 pm

Nearest only works for halving/doubling etc. For things like 29.97 to 24 you have to use optical flow.
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MatthiasHoeller

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 8:09 pm

Uli Plank wrote:In Resolve, it's called "Nearest" and it's under "Frame Interpolation". If your quality is insufficient, play with the other options. Optical Flow will be slow, though.


Yes "Nearest" was the default setting and I used that. I am very satisfied with the result, so thanks again :)
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MatthiasHoeller

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 8:10 pm

CodeTech wrote:In future, you might want to keep Handbrake at the ready. It's a really simple transcoder, and even uses NVENC and NVDEC, so can do what you're asking at something like 300fps.
It's free.


Thanks, I'll keep that in mind. Is it easy to use?
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MatthiasHoeller

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 8:11 pm

Jim Simon wrote:File size = bitrate x duration.

Parameters like resolution and frame rate have no bearing on file size. If you want a smaller file, you need to reduce the bitrate, shorten the program, or both.


Yes I realize the file size influence factors. But I figure that is a very simplistic view, because the bitrate isn't arbitrary, but it must be chosen according to the amount of dataflow necessary to convey the video.

And a video with half the frame rate needs a lower bitrate still looking good, does it not?
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Michael_Andreas

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 8:32 pm

MatthiasHoeller wrote:And a video with half the frame rate needs a lower bitrate still looking good, does it not?


If you look at the bitrate for a GoPro at 1080p, it has exactly the same bitrate from 24 fps to 60 fps. I guess GoPro doesn't know what you know.
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Andrew Kolakowski

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 9:23 pm

Both answers are correct.
It all depends on the codec. You can use same bitrate for 30p and 60p file if you happy with end results in case of eg. h264. For uncompressed/intermediate formats bitrate in most cases scales proportional to fps, so eg. 60p will be twice bigger than 30p.
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Cary Knoop

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 9:53 pm

Optical flow from 60p to 24p works fine (optionally with some slight motion bur)

But the question is why would you want to decimate a 60p video?
What is your deliverable?
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Thom Guida

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Re: How best to reduce framerate by 2

PostMon Nov 11, 2019 10:10 pm

My response a bit off topic.

Marc Wielage wrote:<snip> I didn't know 59.97 was a frame rate, but you can try it and see what happens. <snip>


Hi Marc, I recently made the same mistake (not here), typing 59.97 instead of 59.94 as 29.97 x 2 = 59.94. The mistake typing or saying 59.97 is likely due to the easy access to Titans (no sarcasm at any level) in the business with decades of experience and training, available for feedback. Speaking for myself it can be intimidating to post and we don't know how our questions maybe responded to regardless of our previous monitoring of a forum or the written Moderator ground rules.

Nonetheless, the sincerity and helpfulness of all participating here is very much appreciated.

Thank you all.
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