Myujth

I wrote a little tkinter GUI to handle 4 inputs to ffmpeg. Since the subprocess will take some time i want to status the process. Therefore I use threading so tkinter doesn't freeze while the subprocess is executed.

My problem is that with threading the ffmpeg command outputs the destination file with 0kb and nothing is anymore written to the file. If I use my function without threading everything works, but the GUI is freezing.

Here is the main part of the code:

def ffmpeg(v0,v1,v2,v3):
 cmd = [ path+'ffmpeg.exe',"-y","-i",v0,"-i",v1,"-i",v2,'-i',v3,'-filter_complex',"[0:v][1:v]hstack[top];[2:v][3:v]hstack[bottom];[top][bottom]vstack,format=yuv420p[v]",'-map',"[v]","out.mp4"]
 process = subprocess.Popen(cmd, stdout=subprocess.PIPE,stderr=subprocess.PIPE)
 while True:
 output = process.stdout.readline()
 inpu = process.stderr.readline()
 if output == b'' and process.poll() is not None:
 break
 if output:
 print(output.strip()) # HERE i will insert into tkinter textfield
 rc = process.poll()

def buttonClick(v0,v1,v2,v3):

 #ffmpeg(v0,v1,v2,v3) # This line works
 t = threading.Thread(target=ffmpeg,args=(v0,v1,v2,v3,)) #This doesn't work
 t.start()
 #t.join()

#tkvar list elements are absolute paths to the videofiles
submitButton = Button(mainframe, text="Process Video", command=lambda: buttonClick(tkvar[0].get(),tkvar[1].get(),tkvar[2].get(),tkvar[3].get()))
submitButton.grid(row = 7, column =3)

Why is my thread not working?

The problem was that
process.stdout.readline()
Is always empty since ffmpeg writes always everything to stderr.