Mirror video adding extra frames

Hello, I have been using Shotcut to mirror videos and export them as mp4s. However, the mirrored videos have an extra frame compared to the originals. I am aiming to do some frame by frame analysis so this is quite a significant issue for me, please can someone help inform me why/where an additional frame would be added and if there is anyway to prevent this from happening or account for it?

Both the original and mirror videos are mp4 files and I have been counting the frames with both by uploading them into matlab via the function “implay(video_filepath)”.

Thanks in advance.

What Shotcut version are you using? (Click on Help - About Shotcut)
What Video Mode are you using? (Click on Output, then Properties)
What are the source video properties? (Click on the clip, then Properties)

Version: 21.03.21
Video mode: Automatic - (can’t find an ‘Output’ button?)
Source video: .mp4, 195MB, length = 00:16:22, frame rate = 24.02 frames/second

I think @Hudson555x meant Output in the timeline, as below. Right-click and choose Other->Properties


Perhaps the issue is from the odd frame rate.
You could try Shotcut’s Covert to edit-friendly feature.
It makes a new file from your source video.
With that file start a new project, and see if it takes care of the issue.

Unless you are using the timeline you are not going to see “Output”. Without screenshots, it’s hard at time to guess what is going on. More than likely you have the same odd frame rate video as your source as you left the Video Mode in Automatic.

I’m guessing if you ran your source file through Media Info, it will show you have a variable frame rate. Sometimes Shotcut will show this if it is variable, but not all of the time.

I also don’t know if you changed any settings when exporting, or if you just left everything as default. If everything was export as default settings, it would have taken on the source video frame rate, although not sure if Shotcut produces a variable frame rate video (if the source is variable frame rate).

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The OP is not using the timeline.
That option is greyed out.

Shotcut always exports constant frame rate. So the extra frame(s) are coming from converting the VFR source to CFR output. The VFR frame rate is probably rounded to the nearest CFR frame rate (I don’t know the exact algorithm). But the difference between the two is how frames get duplicated to meet the CFR frame rate.

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Thank you all for your responses. Upon further investigation with a specially made shorter video (6 very different frames), shotcut was duplicating the last frame in the video. This is simple to account for in post-analysis so my issue can be considered resolved. Thank you all for your help.

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