Add auto dectection of resolution using mplayer2

This commit is a proof-of-concept.
Two problems needed to be solved.

1. The 1st comment file may not have a matching video file
2. The video file may not have .mp4 extension

danmaku2ass.py

@@ -21,6 +21,7 @@
 import os
 import random
 import re
+import subprocess
 import sys
 import time
 import xml.dom.minidom
@@ -814,13 +815,46 @@ def GetCommentProcessor(input_file):
     return CommentFormatMap[ProbeCommentFormat(input_file)]
 
 
+# Use mplayer2 to get the resolution info of the video file
+# having the same name as the comment file
+def get_resolution(file_name):
+    try:
+        width = 0
+        height = 0
+        media_info = subprocess.check_output(["mplayer", "-really-quiet"
+                                          , "-ao", "null", "-vo", "null"
+                                          , "-identify", "-frames", "0"
+                                          , file_name]).decode(
+                                              "utf-8").split("\n")
+        for item in media_info:
+            if "ID_VIDEO_WIDTH=" in item:
+                width = int(item.split("=")[1])
+            elif "ID_VIDEO_HEIGHT=" in item:
+                height = int(item.split("=")[1])
+        if width > 0 and height > 0:
+            return [width, height]
+        else:
+            raise Exception()
+    except:
+        print()
+        print("Resolution is not specified by --size WIDTHxHEIGHT")
+        print("and fail to read resolution info using mplayer")
+        print()
+        print("Option 1: set the size manually using --size WIDTHxHEIGHT")
+        print()
+        print("Option 2: rename the video so that it has the same name")
+        print("as the comment file and install mplayer2 if")
+        print("it is not already pre-installed on your distro")
+        print()
+
+
 def main():
     logging.basicConfig(format='%(levelname)s: %(message)s')
     if len(sys.argv) == 1:
         sys.argv.append('--help')
     parser = argparse.ArgumentParser()
     parser.add_argument('-o', '--output', metavar=_('OUTPUT'), help=_('Output file'))
-    parser.add_argument('-s', '--size', metavar=_('WIDTHxHEIGHT'), required=True, help=_('Stage size in pixels'))
+    parser.add_argument('-s', '--size', metavar=_('WIDTHxHEIGHT'), help=_('Stage size in pixels'))
     parser.add_argument('-fn', '--font', metavar=_('FONT'), help=_('Specify font face [default: %s]') % _('(FONT) sans-serif')[7:], default=_('(FONT) sans-serif')[7:])
     parser.add_argument('-fs', '--fontsize', metavar=_('SIZE'), help=(_('Default font size [default: %s]') % 25), type=float, default=25.0)
     parser.add_argument('-a', '--alpha', metavar=_('ALPHA'), help=_('Text opacity'), type=float, default=1.0)
@@ -834,8 +868,15 @@ def main():
         width, height = str(args.size).split('x', 1)
         width = int(width)
         height = int(height)
-    except ValueError:
-        raise ValueError(_('Invalid stage size: %r') % args.size)
+    except:
+        # Get the res of the 1st file, assume the rest are the same
+        #
+        # Two problems need to be solved:
+        # 1. The 1st comment file may not have a matching video file
+        # 2. The video file may not have .mp4 extension
+        res = get_resolution(args.file[0].replace(".xml", ".mp4"))
+        width = res[0]
+        height = res[1]
     Danmaku2ASS(args.file, args.output, width, height, args.protect, args.font, args.fontsize, args.alpha, args.duration_marquee, args.duration_still, args.reduce)