README: add video overlay example

README.rst

@@ -122,6 +122,45 @@ Logging, Properties, Python Key Bindings, Screenshots and youtube-dl
 
     del player
 
+Video overlays
+..............
+
+.. code:: python
+
+    #!/usr/bin/env python3
+    import time
+    from PIL import Image, ImageDraw, ImageFont
+    import mpv
+
+    player = mpv.MPV()
+
+    player.loop = True
+    player.play('test.webm')
+    player.wait_until_playing()
+
+    font = ImageFont.truetype('DejaVuSans.ttf', 40)
+
+    while not player.core_idle:
+
+        time.sleep(0.5)
+        overlay = player.create_image_overlay()
+
+        for pos in range(0, 500, 5):
+            ts = player.time_pos
+            if ts is None:
+                break
+
+            img = Image.new('RGBA', (400, 150),  (255, 255, 255, 0))
+            d = ImageDraw.Draw(img)
+            d.text((10, 10), 'Hello World', font=font, fill=(0, 255, 255, 128))
+            d.text((10, 60), f't={ts:.3f}', font=font, fill=(255, 0, 255, 255))
+
+            overlay.update(img, pos=(2*pos, pos))
+            time.sleep(0.05)
+
+        overlay.remove()
+
+
 Playlist handling
 .................
 
@@ -187,7 +226,7 @@ called once the player is done loading the file and starts playing. An easy way
 
     player = mpv.MPV()
     player.play('test.webm')
-    player.wait_for_property('core-idle', lambda idle: not idle)
+    player.wait_until_playing()
     player.sub_add('test.srt')
     player.wait_for_playback()