The input video is yuv420p which requires both dimensions to be divisible by 2 due to subsampling. When a height of 360 is requested, the calculated width is 871, which is not divisible by 2, and transcoding fails.
This can be fixed by using -vf scale=w=-2:h=360 instead of setting the width to -1. Using -2 will calculate a width that is divisible by 2 which will satisfy the resolution requirements of yuv420p.
Thank you @DRM and @Austin, you guys are experts.
Making a quick update v1.044 now addressing this issue, will update in 10ish minutes.
You’re welcome. 
The updated version fixed the issue.
There’s a slight issue I found. The script doesn’t recognize this character: “
I made a test file and put as the name: “Hello“
It wouldn’t make the proxy and it gave me this error message:
D:\├┤Hello├┤.mp4: No such file or directory
@DRM I tried to type an " in the filename to emulate your situation, then I found this:
A filename cannot contain any of the following characters: \ / : * ? " < > |
How do you get a file with " " in the filename?
It’s actually not the same character.
“ and " are two different characters. Copy and paste the one I posted and see what happens.
If it is a special quotation mark, it should be fine, it is treated the same way like Chinese or Korean characters.
Did some tests, copy the “hello” filename from your post to my file, and proxy created just fine.
Have you edited the batch file manually? Because some text editors will make the text charset or file encoder to Unicode or something, if a special character is met. This will lead to “file not found”.
This tool is fantastic looking, any chance we’ll see a few options added for resolution and format of the video/audio?
@D_S Hey there, I try to keep this tool as simplistic as possible. Adding too many options, it ends up to be another “Handbrake” right? 
Some options are in my mind, like choosing 360p for low-end computers, or 720p for professional workstations. What do you think?
Since the native “proxy editing” is on the Shotcut Roadmap, this is only a temporary tool before the “proxy editing” is officially supported. There is no point to invest too much time in improving it.
I’d definitly appreciate a 360/720 toggle and maybe a lossless toggle for the formats? especially when you’re coming from a 4k source 360 is a long way to go down.
A small suggestion for the Lossless Audio version:
Can you have it name all the files differently on that version? Something like:
_ fastproxyLA _
(LA for “Lossless Audio”)
That way it could differentiate between files made with that version compared to the regular version?
It’d also be nice if it would say “Shotcut Video Proxy Maker Lossless Audio” on the top of the window to also help separate it from the regular one.
Edit:
Now that I think about it, if you are thinking about adding a 360p and 720p option, why not also add the audio options(ac-3 and lossless) as well and just make it one tool instead of two?
@D_S Converting either to 360p or 720p, the quality is already lost. There is no point to use lossless format.
If you are talking about “original resolutions lossless format”, the Shotcut build-in “Convert to edit-friendly” function will serve you better.
And 720p is overkill already. The “preview window” is most likely to be around 500p for most of the users here. So a 450p make more sense.
On my mid-range PC, my test result is:
360p, adding 3~4 filters it can still be smooth, even during transitions;
450p, can be smooth with 1~2 easy filters;
720p, smooth only without filters.
For the purpose of the “smooth proxy”, I would prefer to push the quality higher in low resolutions(the amount of pixels matters), rather than using higher resolutions.
@DRM hey good advice. That lossless audio version is a thanksgiving to @Austin only as his workflow involve fetching good audio out of the editor. Never thought anyone else would want to use it.
So the 360p option has been removed? It’s only 450p and 720p now?
@DRM errr… yea…I tested and tested on my mid-to-low end computer, the 360p and the 450p didn’t make significant difference in editing smoothness. So maybe the 450p is a better way to go as the default?
(the quality and smoothness differences are very minor. If you had 360p made, don’t bother remake them.)
Perhaps I used the term lossless incorrectly, I was more meaning to say “uncompressed” so there’s no i-frame’s to worry about(perhaps you’re already doing that however and I skipped past that trying to get caught up)
Regarding the preview window I ususally cut on a 4k monitor so perhaps I’m using things at a less than typical scale.
Just saw the updated version and it looks fantastic
Thanks for taking the time to update it again! 
You said that with 360p you can add 3-4 filters and it be smooth even during transitions but with 450p it’s smooth up with only 1-2 filters. So if you add 3-4 filters plus a transition with 450p, it isn’t smooth?
Also, is there a noticeable size difference when exporting as 360p versus 450p?
@DRM The thing is, by doing side-by-side comparison, 450p is definitely little less smooth than 360p. The difference is not obvious, there is no clear line between 2 and 3 filters, using them double blindly you often can’t tell.
On the 360p, some bit-rates are wasted on “refining” the existing pixels. Throw another 20mbps into the 360p will not bring up any more picture details. The 450p maybe a good balanced value and it is close to the native size of the Shotcut preview on 1080p monitors. (720p is close to the preview size on the 4k monitors. Peace and harmony).
The file size is likely to be 40% larger, depends on the scenes.
@D_S oh hey I think now I understand you. I thought about that, it seems h264 is a pretty good balance among the speed/size/quality.
Hi @KKnBB , just thought I’d repeat the link to your proxy tool here so folks don’t have to scroll to the top of this (long) thread to get the latest version - if that’s OK with you? Great work!! 
