Add default global scale value if missing in the annotation hook (#647)

### Add default global scale value if missing

### Summarize your change.

A default global scale value is calculated based on the aspect ratio of
the first source if it couldn't be obtained from the OTIO.

### Describe the reason for the change.

When no `available_image_bounds` is present in the OTIO, no global scale
value was being calculated. This was causing an issue where the
annotations couldn't be displayed in RV during a Live Review Session.

### Describe what you have tested and on which operating system.

Successfully test on MacOS

---------

Signed-off-by: Éloïse Brosseau <[email protected]>

src/plugins/rv-packages/otio_reader/annotation_hook.py

@@ -6,6 +6,7 @@
 # *****************************************************************************
 
 
+import logging
 import effectHook
 import opentimelineio as otio
 from rv import commands, extra_commands
@@ -58,6 +59,24 @@ def hook_function(in_timeline, argument_map=None) -> None:
             )
 
             global_scale = argument_map.get("global_scale")
+            if global_scale is None:
+                logging.warning(
+                    "Unable to get the global scale, using the aspect ratio of the first media file"
+                )
+                try:
+                    first_source_node = commands.sourcesAtFrame(0)[0]
+                    media_info = commands.sourceMediaInfo(first_source_node)
+                    height = media_info["height"]
+                    aspect_ratio = media_info["width"] / height
+                except Exception:
+                    logging.exception(
+                        "Unable to determine aspect ratio, using default value of 16:9"
+                    )
+                    aspect_ratio = 1920 / 1080
+                finally:
+                    scale = aspect_ratio / 16
+                    global_scale = otio.schema.V2d(scale, scale)
+
             points_property = f"{pen_component}.points"
             width_property = f"{pen_component}.width"