import ffmpeg

packet_size = 4096

process = (
    ffmpeg
        .input('rtsp://172.22.246.207/extron1')
        #.input('rtsp://172.22.246.207/extron3')
        .output('/tmp/test.jpg', vframes=1)
        #.output('-', format='h264')
        .run_async(pipe_stdout=True)
)

while process.poll() is None:
    packet = process.stdout.read(packet_size)