Video quality drop for sped up clips

Hi all!
I’m editing a video of a bike ride. 4K from gopro 10, I’m using proxy files.
I didn’t cut anything, just figured I’d speed up less interesting parts, in the exported file, normal speed portions are ok, but anything that’s 3x speed is much lower quality. Is there a setting for exporting that would ensure constant quality?

Thank you!

Can you share some screenshots to give examples.

Since you are using proxy files, maybe the proxy is being used to render the exported file. You could try to disable proxy in your project and see if that helps.

I can’t edit this without Proxy, my machine can’t handle it. It worked great before when I was just cutting for editing, but changing speed really messes with the output. I’ll upload screenshots when I get home.

That is understandable. But if you are trying to export, I presume that you are done editing. Proxy can be turned on and off easily. I suggest to turn off proxy temporarily, and then see if the quality improves.

I see, interesting, I will, thanks!

My second attempt is still exporting (with Proxy turned off) if you don’t mind, take a look at the video here (switch to 4K). Results on youtube are the same as local when viewed with VLC.

It does look like it could be rendering from the proxy file. Can you post your project file as an attachment?

From Shotcut version 22.06 release notes:

  • Fixed repairing a project with Settings > Proxy > Use Proxy on saves proxy file paths into repaired project file.

@brian It’s a massive file that I already deleted it, I do have it on gopro cloud, but I’m a bit hesitant to share publicly since there are some personal conversation in the video. Any alternatives?

@shotcut Thanks for the link, I’m already on 22.06.23. Do you mind elaborating on what what this note means? As in, is there a way to repair exported file, or does it mean that the issue with exporting while proxy ON is fixed?

Thank you both for your time!

I’m just asking for the .mlt file. We would not need any of the video files. The MLT file is just a tiny text file.

But did you start the project on this version? If not, then the problem could have occurred before upgrade, which cannot fix a damaged project.

Do you mind elaborating on what what this note means?

Did you ever get a warning dialog upon opening the project that some files are missing or it needed repair? If so, and proxy was on, then it would replace the source clips with the proxy. So, at export time, it is unable to replace the proxy with the source because it lost track of it.

Turn off proxy, go to the clip you think has a problem. Check the filename in Properties. Is it correct? If not, to fix it:

  1. Open the correct source clip in the Source player
  2. Set the in point to what you used before or want now.
  3. right click the timeline clip and choose Replace.

@brian Wow, I completely missed that. :slight_smile: Here you go:
Andrew mountain bike.mlt (71.6 KB)

@shotcut I did start on this version, and I never noticed the dialog box in question.My computer is churning trough a huge job of proxying another project overnight. I will check in the morning and let you know.

Thank you both!

I looked in your project file and I do not see any references to proxy files.

Now I wonder if you just need to change your export settings. What export settings are you using?

Using these. My thought is, in my limited video encoding understanding, that potentially GOP is too high, so it might need to “guess” too much between I frames. I do wonder why wouldn’t it drop quality on non sped up portions.
If that is the case, what would be better to increase, Codec->Quality or decrease GOP, as in what would make for less of a file size penalty. Maybe more B frames? This 15 min video came out to be 30GB in 55%. I tried with just increasing Quality to 85 and that got it to whooping 72GB :). I mean, it is what it is, but I was surprised. Original GoPro footage is encoded in .265, but from youtubes page they say they play nicer with .264.
Once again, thank you for being so responsive. It’s amazing that open source project has vastly better support than commercial products. I will make sure this is known.


Mountain biking footage is notoriously difficult to compress well due to fast moving, highly variated forest foliage. When you speed it up it become even more challenging because the change between frames is greater. You can upload HEVC to YouTube just fine, and when you use NVIDIA hardware encoder for HEVC it exports faster with smaller size. You can ignore advice that YouTube works better with H.264. Why would it? Could YouTube have gotten anywhere as large as it is by being picky about its input? What about all the people uploading unedited HEVC GoPro footage? Possibly the only difference it may make is how fast it is processed before publishing.

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Increase quality

If YouTube is your destination, then there isn’t much disadvantage to having a larger file size. It will just take a little longer to upload.

@brian Thank you, I’ll do that for my next video. I made my peace with this one as one of my first attempts, so I’ll let it be.

@shotcut In your opinion, is there any reason to choose .264 over HVEC anymore, or should I just default to HVEC for all my exports, if the intention is to upload to youtube (mostly)?

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