Update inference_utils.py

Improves accuracy of frame rate. See https://github.com/PyAV-Org/PyAV/issues/580

inference_utils.py

@@ -31,7 +31,7 @@ class VideoReader(Dataset):
 class VideoWriter:
     def __init__(self, path, frame_rate, bit_rate=1000000):
         self.container = av.open(path, mode='w')
-        self.stream = self.container.add_stream('h264', rate=round(frame_rate))
+        self.stream = self.container.add_stream('h264', rate=f'{frame_rate:.4f}')
         self.stream.pix_fmt = 'yuv420p'
         self.stream.bit_rate = bit_rate