Comment by sorenjan

I've never tried doing frame perfect clips like that, that does sound annoying. But from a cursory read of the source, I don't think this program will solve that issue either? Because the time stamps in your examples are all correct, and the TUI is using ffmpeg with -ss and -t as well.

  func BuildFFmpegCommand(opts ExportOptions) string {
   output := opts.Output
   if output == "" {
    output = generateOutputName(opts.Input)
   }
   duration := opts.OutPoint - opts.InPoint
  
   args := []string{"ffmpeg", "-y",
    "-ss", fmt.Sprintf("%.3f", opts.InPoint.Seconds()),
    "-i", filepath.Base(opts.Input),
    "-t", fmt.Sprintf("%.3f", duration.Seconds()),
   }

I think the best way of getting frame accurate clips like that is putting the starting time after the input (or rather before the output), which decodes the video up to that time, and reencode it instead of copying. Both of these commands gives the expected output:

  ffmpeg -i master.mp4 -ss 0 -t 1 -c:v libx264 green.mp4
  ffmpeg -i master.mp4 -ss 1 -t 1 -c:v libx264 red.mp4