B4J Question video player timing with saving the frame

Dim vf As String = cboVideoFiles.Items.Get(f)   'video file name
Dim piece As Long = videotime2 - videotime1    'ticks
Dim freq As Float = split_qty / (piece/1000)
Dim output_file As String = File.Combine(output_folder, "output_" & DateTime.Now & "_" & DeviceID & "_%05d" & ".jpg")
Slice(TicksToTime(videotime1), File.Combine(ProjectFolder, vf), freq, output_file)

Sub Slice(from As String, video As String, freq As String, out As String)
    'ffmpeg -i input_file.mp4 -ss 00:03:45 -vframes 1 output.jpg
    Dim ff As String = File.Combine(ffmpeg_folder, "ffmpeg.exe")
    Dim Args As List
    Args.Initialize
    Args.Add("-ss")
    Args.Add(from)    'seconds
    Args.Add("-i")
    Args.Add(video)
    Args.Add("-r")
    Args.Add(NumberFormat2(freq, 1, 2, 2, False))
    Args.Add("-qscale:v")
    Args.Add("5")    '3=86%, 5=76% JPG quality
    Args.Add("-vframes")
    Args.Add((split_qty + 1).As(String))
    Args.Add(File.GetName(out))
             
             
    Dim sh As Shell
    sh.Initialize("ffmpeg", ff, Args)
    sh.WorkingDirectory = File.GetFileParent(out)
    sh.Run(-1)
    wait for ffmpeg_ProcessCompleted (Success As Boolean, ExitCode As Int, StdOut As String, StdErr As String)
End Sub

Sub TicksToTime (t As Long) As String
    Dim hours As Int = t / 1000 / 60 / 60
    Dim mins As Int = ((t / 1000) - (hours * 60 * 60)) / 60
    Dim secs As Int = ((t / 1000) - (hours * 60 * 60) - (mins * 60))
    Dim msecs As Float = ((t / 1000) - (hours * 60 * 60) - (mins * 60) - secs) * 1000
    Dim res As String = NumberFormat2(hours, 2, 0, 0, False) & ":" & NumberFormat2(mins, 2, 0, 0, False) & ":" & NumberFormat2(secs, 2, 0, 0, False) 

    Return res
End Sub