Decimal FPS is not supported

[TheTDD]

Mokose UC70 webcam supports following formats:

ioctl: VIDIOC_ENUM_FMT
        Index       : 0
        Type        : Video Capture
        Pixel Format: 'MJPG' (compressed)
        Name        : Motion-JPEG
                Size: Discrete 1920x1080
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 3840x2160
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 1280x720
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 2048x1536
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 2560x1440
                        Interval: Discrete 0.033s (30.000 fps)
                Size: Discrete 640x480
                        Interval: Discrete 0.033s (30.000 fps)

        Index       : 1
        Type        : Video Capture
        Pixel Format: 'YUYV'
        Name        : YUYV 4:2:2
                Size: Discrete 1920x1080
                        Interval: Discrete 0.500s (2.000 fps)
                Size: Discrete 3840x2160
                        Interval: Discrete 1.000s (1.000 fps)
                Size: Discrete 1280x720
                        Interval: Discrete 0.133s (7.500 fps)
                        Interval: Discrete 0.200s (5.000 fps)
                        Interval: Discrete 0.500s (2.000 fps)
                Size: Discrete 2048x1536
                        Interval: Discrete 0.500s (2.000 fps)
                Size: Discrete 2560x1440
                        Interval: Discrete 0.500s (2.000 fps)
                Size: Discrete 640x480
                        Interval: Discrete 0.033s (30.000 fps)
                        Interval: Discrete 0.040s (25.000 fps)
                        Interval: Discrete 0.050s (20.000 fps)
                        Interval: Discrete 0.067s (15.000 fps)
                        Interval: Discrete 0.133s (7.500 fps)
                        Interval: Discrete 0.200s (5.000 fps)
                        Interval: Discrete 0.500s (2.000 fps)
                        Interval: Discrete 1.000s (1.000 fps)

trying to set resolution 1280x720 and fps to 7.5, µstreamer reports:

Invalid value for '--desired-fps=7.5': min=0, max=120

and does not start capture.

by omitting the -f, µstremer reports following:

-- ERROR [1300050.155 stream] -- Invalid HW FPS numerator: 2 != 1

and starting capture with desired FPS:

Driver Info (not using libv4l2):
        Driver name   : uvcvideo
        Card type     : UC70: UC70
        Bus info      : usb-0000:06:00.0-2
        Driver version: 4.18.6
        Capabilities  : 0x84A00001
                Video Capture
                Streaming
                Extended Pix Format
                Device Capabilities
        Device Caps   : 0x04200001
                Video Capture
                Streaming
                Extended Pix Format
Priority: 2
Video input : 0 (Camera 1: ok)
Format Video Capture:
        Width/Height      : 1280/720
        Pixel Format      : 'YUYV'
        Field             : None
        Bytes per Line    : 2560
        Size Image        : 1843200
        Colorspace        : sRGB
        Transfer Function : Default
        YCbCr/HSV Encoding: Default
        Quantization      : Default
        Flags             : 
Crop Capability Video Capture:
        Bounds      : Left 0, Top 0, Width 1280, Height 720
        Default     : Left 0, Top 0, Width 1280, Height 720
        Pixel Aspect: 1/1
Selection: crop_default, Left 0, Top 0, Width 1280, Height 720
Selection: crop_bounds, Left 0, Top 0, Width 1280, Height 720
Streaming Parameters Video Capture:
        Capabilities     : timeperframe
        Frames per second: 7.500 (15/2)
        Read buffers     : 0

I'd be thankful if you add support for decimal FPS and fix the error with FPS numerator. Thanks in advance!