fix colorspace bug & support multi-gpu and multi-processing (#312)

* fix colorspace bug of ffmpeg stream, add multi-gpu and multi-processing suport for inference_realesrgan_video.py

* fix code format

Co-authored-by: yanzewu <yanzewu@tencent.com>

realesrgan/utils.py

@@ -26,7 +26,7 @@ class RealESRGANer():
         half (float): Whether to use half precision during inference. Default: False.
     """
 
-    def __init__(self, scale, model_path, model=None, tile=0, tile_pad=10, pre_pad=10, half=False):
+    def __init__(self, scale, model_path, model=None, tile=0, tile_pad=10, pre_pad=10, half=False, device=None):
         self.scale = scale
         self.tile_size = tile
         self.tile_pad = tile_pad
@@ -35,7 +35,7 @@ class RealESRGANer():
         self.half = half
 
         # initialize model
-        self.device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')
+        self.device = torch.device('cuda' if torch.cuda.is_available() else 'cpu') if device is None else device
         # if the model_path starts with https, it will first download models to the folder: realesrgan/weights
         if model_path.startswith('https://'):
             model_path = load_file_from_url(