Kbit/s changes after export - solved

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Lars Andersson

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Kbit/s changes after export - solved

PostFri Oct 15, 2021 7:19 am

Hi! I mainly digitze 8mm film and using several software for this. Trying to use Resolve Sttudio much more and my fist question is why kbit/s changes all the time. Just and example:

The first film I import is a move-clip and has 160957 kbit/s. After colorgrading I export it as a mp4/H264 and now it's 96654 kbit/s. But then I import the last file and use Neat Video and now within the same project it goes down to 18769 kbit/s. Then I import it a last time and just change the speed and the final result is 12053 kbit/s. Why does this happen with the same project settings?
Last edited by Lars Andersson on Sat Oct 16, 2021 2:35 pm, edited 1 time in total.
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Andy Mees

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Re: Kbit/s changes after export

PostFri Oct 15, 2021 12:48 pm

Hi Lars

We can't see what media you were working with; we can't see its content and we can't see its codec, we can't see what you did with it and we can't see the settings you used to create the exported clips with the different data rates ... so consider everything that follows as a very broad response.

Your exported media's file size / data rate is determined by your export settings.
Specifically, your choice of codec (encoder/decoder) determines by what method your video data will be compressed. Your original file's compression settings produced a file that was 160,957 kbit/s... you imported that file and Resolve decompressed for editing /playback, so you could work with it. You did your thing, and then you exported your new clip ... the settings you used in this last step (the export) will not have been the exact same settings used to produce the original clip... and indeed it produced a file that was 96,654 kbit/s.

With respect to Neat Video affecting your end point file size / data rate, remember that the codec of your choice, regardless of that choice, is encoding all the video data it is given ie the good data (eg the nice picture) AND any bad data (eg any noise). By cleaning up the noise with Neat Video, you are potentially reducing the amount of bad data that needs to be encoded by replacing it with nice a clean/smooth picture that's much easier/more efficient to encode, thus the second export produced a file that was 18,769 kbit/s.

Your final step was to change the speed... and I'm assuming you mean you slowed it down, because less movement in the picture means less change from frame to frame, and less change from frame to frame can mean less data that needs to be used to encode those frame changes. Hence the data rate in your final result dropping to 12053 kbit/s.

Hope that helps you visualise what's happening.
heers
Andy
Let's have a return to the glory days, when press releases for new versions included text like "...with over 300 new features and improvements that professional editors and colorists have asked for."
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Lars Andersson

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Re: Kbit/s changes after export

PostFri Oct 15, 2021 1:10 pm

Thanks for the input!

I always use the same setting in my project and in this case it's MP4, H.264, 25 fps. I can understand that it goes down after Neat Video but I think the difference is rather huge: from 96654 kbit/s to 18769 kbit/s. In the last step I make the clip longer. The original file contains unique frames from the 8mm film and I need to stretch it out so the speed will be normal. Otherwise it would look like an old Chaplin movie. So 2min 20 sec gets ca 3 min 30 sec instead. My concern is mainly that I fear the queslity is going down becuase of the lower kbit/s rate in the end product. Maybe I'm wrong.
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ZRGARDNE

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Re: Kbit/s changes after export

PostFri Oct 15, 2021 2:18 pm

Don't use the quality presets in resolve (medium, best, etc) they are junk.

Resolve has Variable bitrate encoding, but the feature has no documentation and I would thus consider it unusable.

H.265 encoding is not included in free on Windows (is on mac). H.264 is available. 265 will reproduce similar quality to 264 at about 50% the bitrate.

You can manually set the export bitrate in Resolve to whatever you want, and you basically have to as the presets are junk and the VBR tool is unusable.

I personally choose to avoid all that and export DNxHR HQ from resolve, it is essentially lossless. Then use Handbrake to compress to H.265 using VBR
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Andy Mees

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Re: Kbit/s changes after export

PostFri Oct 15, 2021 2:49 pm

Lars Andersson wrote:I always use the same setting in my project and in this case it's MP4, H.264, 25 fps.


MP4 is the wrapper ... the container that the video data sits inside.
H.264 is the codec ... its a very highly compressed lossy delivery codec. It's not a good codec for digitising your 8mm film because its taking the full original input video data (by whatever method you are using), immediately highly compressing that data and in the process throwing away (hence 'lossy') some of that data... any work you do thereafter on this freshly captured digital copy is working from this reduced data set. H.264 is also not a good working and / or intermediate codec... you note multiple passes of import and export in your workflow, each time re-compressing and therefore potentially throwing away more and more of the image data / image quality each time.


Lars Andersson wrote:I can understand that it goes down after Neat Video but I think the difference is rather huge: from 96654 kbit/s to 18769 kbit/s.


Without any real point of reference to your actual original film / digitised video content, what settings you used in Neat Video, how it looked before and after etc and to be honest, without validating that the settings / encoding profile is unchanged each time, it's impossible really to simply guess whether its too much difference. Its not impossible that you could see such a drastic difference tho.

Lars Andersson wrote:My concern is mainly that I fear the quality is going down because of the lower kbit/s rate in the end product. Maybe I'm wrong.


Nope, you are right. You are undoubtedly throwing away potential image quality.
Let's have a return to the glory days, when press releases for new versions included text like "...with over 300 new features and improvements that professional editors and colorists have asked for."
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Lars Andersson

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Re: Kbit/s changes after export

PostFri Oct 15, 2021 3:17 pm

Thanks for the input all of you!

In what format should I export then? I need something that will work for eveyone of my customers. I digitize their films to USB then thay should be able to view it on their TV or computer. For now it seems the TV have a harder time with some formats. So with MP4 and H264 everyone of my customers have no problems, it just works fine. So what format is the best if I want high quality for my customers?
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Andy Mees

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Re: Kbit/s changes after export

PostFri Oct 15, 2021 3:57 pm

H264 is a suitable delivery codec, Lars, and will suit most of your clients... however, if you used a higher quality codec to digitise the source ie to create your digital intermediate eg ProRes 422 HQ or DNxHR HQ and then you worked from that higher quality source throughout your production pipeline, you would be able to provide your clients with a higher quality final product. Albeit that end-product would most often be H264, you would have preserved the best possible quality throughout the process ... plus, if you offered it at a premium, some customers would likely happily pay extra for a copy of the master quality export together with their H264 version.
Let's have a return to the glory days, when press releases for new versions included text like "...with over 300 new features and improvements that professional editors and colorists have asked for."
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Lars Andersson

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Re: Kbit/s changes after export SOLVED

PostSat Oct 16, 2021 2:37 pm

Thanks for the tip!

Now I use another format when exporting and only use MP4/H.264 for the last one and that gives me 5 times better kbit/s.

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