diff --git a/automation/vapoursynth/aegisub_vs.py b/automation/vapoursynth/aegisub_vs.py
index 1eca5f5d3..6ccd7b9b9 100644
--- a/automation/vapoursynth/aegisub_vs.py
+++ b/automation/vapoursynth/aegisub_vs.py
@@ -28,6 +28,8 @@ other data.
 import os
 import os.path
 import re
+from enum import Enum
+from tkinter.messagebox import askyesno
 from collections import deque
 from typing import Any, Dict, List, Tuple
 
@@ -216,25 +218,36 @@ def save_keyframes(filename: str, keyframes: List[int]):
         f.write("".join(f"{n}\n" for n in keyframes))
 
 
-def try_get_keyframes(filename: str, default: str | List[int]) -> str | List[int]:
-    """
-    Checks if a keyframes file for the given filename is present and, if so,
-    returns it. Otherwise, returns the given list of keyframes.
-    """
-    kffilename = make_keyframes_filename(filename)
-
-    return kffilename if os.path.exists(kffilename) else default
+class GenKeyframesMode(Enum):
+    NEVER = 0
+    ALWAYS = 1
+    ASK = 2
 
 
-def get_keyframes(filename: str, clip: vs.VideoNode, **kwargs: Any) -> str:
+def get_keyframes(filename: str, clip: vs.VideoNode, fallback: str | List[int],
+                  generate: GenKeyframesMode = GenKeyframesMode.ASK, **kwargs: Any) -> str | List[int]:
     """
-    When not already present, creates a keyframe file for the given clip next
+    Looks for a keyframes file for the given filename.
+    If no file was found, this function can generate a keyframe file for the given clip next
     to the given filename using WWXD or Scxvid (see the make_keyframes docstring).
+    Whether or not keyframes are generated depends on the `generate` argument.
+    Depending on the `generate` argument, the function will
+    - always generate keyframes when no file was found
+    - never generate keyframes when no file was found
+        (and return the fallback keyframes instead)
+    - show a dialog to ask the user whether keyframes should be
+      generated or not
     Additional keyword arguments are passed on to make_keyframes.
     """
     kffilename = make_keyframes_filename(filename)
 
     if not os.path.exists(kffilename):
+        if generate == GenKeyframesMode.NEVER:
+            return fallback
+        if generate == GenKeyframesMode.ASK and not askyesno("Generate Keyframes", \
+                "No keyframes file was found for this video file.\nShould Aegisub detect keyframes from the video?\nThis will take a while.", default="no"):
+            return fallback
+
         vs.core.log_message(vs.MESSAGE_TYPE_INFORMATION, "No keyframes file found, detecting keyframes...\n")
         keyframes = make_keyframes(clip, **kwargs)
         save_keyframes(kffilename, keyframes)
diff --git a/src/libresrc/default_config.json b/src/libresrc/default_config.json
index c075789eb..a93416e41 100644
--- a/src/libresrc/default_config.json
+++ b/src/libresrc/default_config.json
@@ -374,7 +374,7 @@
 			},
 			"VapourSynth" : {
 				"Log Level": "Information",
-				"Default Script" : "# This default script will load a video file using LWLibavSource.\n# It requires the `lsmas` plugin.\n# See ?data/automation/vapoursynth/aegisub_vs.py for more information.\n\nimport vapoursynth as vs\nimport time\nimport aegisub_vs as a\na.set_paths(locals())\n\nclip, videoinfo = a.wrap_lwlibavsource(filename)\nclip.set_output()\n__aegi_timecodes = videoinfo[\"timecodes\"]\n__aegi_keyframes = videoinfo[\"keyframes\"]\n\n# Uncomment the first following line to read keyframes from a file when present.\n#__aegi_keyframes = a.try_get_keyframes(filename, __aegi_keyframes)\n\n# Uncomment the following line to automatically generate keyframes at scene changes. This will take some time when first loading a video.\n#__aegi_keyframes = a.get_keyframes(filename, clip)\n\n# Check if the file has an audio track. This requires the `bas` plugin.\n__aegi_hasaudio = 1 if a.check_audio(filename) else 0"
+				"Default Script" : "# This default script will load a video file using LWLibavSource.\n# It requires the `lsmas` plugin.\n# See ?data/automation/vapoursynth/aegisub_vs.py for more information.\n\nimport vapoursynth as vs\nimport time\nimport aegisub_vs as a\na.set_paths(locals())\n\nclip, videoinfo = a.wrap_lwlibavsource(filename)\nclip.set_output()\n__aegi_timecodes = videoinfo[\"timecodes\"]\n__aegi_keyframes = videoinfo[\"keyframes\"]\n\n# Uncomment this line to make Aegisub look for a keyframes file for the video, or ask to detect keyframes on scene changes if no file was found.\n# You can also change the GenKeyframesMode. Valid values are NEVER, ALWAYS, and ASK.\n#__aegi_keyframes = a.get_keyframes(filename, clip, __aegi_keyframes, generate=a.GenKeyframesMode.ASK)\n\n# Check if the file has an audio track. This requires the `bas` plugin.\n__aegi_hasaudio = 1 if a.check_audio(filename) else 0"
 			}
 		}
 	},
diff --git a/src/libresrc/osx/default_config.json b/src/libresrc/osx/default_config.json
index a05c04f68..80b54b52e 100644
--- a/src/libresrc/osx/default_config.json
+++ b/src/libresrc/osx/default_config.json
@@ -374,7 +374,7 @@
 			},
 			"VapourSynth" : {
 				"Log Level": "Information",
-				"Default Script" : "# This default script will load a video file using LWLibavSource.\n# It requires the `lsmas` plugin.\n# See ?data/automation/vapoursynth/aegisub_vs.py for more information.\n\nimport vapoursynth as vs\nimport time\nimport aegisub_vs as a\na.set_paths(locals())\n\nclip, videoinfo = a.wrap_lwlibavsource(filename)\nclip.set_output()\n__aegi_timecodes = videoinfo[\"timecodes\"]\n__aegi_keyframes = videoinfo[\"keyframes\"]\n\n# Uncomment the first following line to read keyframes from a file when present.\n#__aegi_keyframes = a.try_get_keyframes(filename, __aegi_keyframes)\n\n# Uncomment the following line to automatically generate keyframes at scene changes. This will take some time when first loading a video.\n#__aegi_keyframes = a.get_keyframes(filename, clip)\n\n# Check if the file has an audio track. This requires the `bas` plugin.\n__aegi_hasaudio = 1 if a.check_audio(filename) else 0"
+				"Default Script" : "# This default script will load a video file using LWLibavSource.\n# It requires the `lsmas` plugin.\n# See ?data/automation/vapoursynth/aegisub_vs.py for more information.\n\nimport vapoursynth as vs\nimport time\nimport aegisub_vs as a\na.set_paths(locals())\n\nclip, videoinfo = a.wrap_lwlibavsource(filename)\nclip.set_output()\n__aegi_timecodes = videoinfo[\"timecodes\"]\n__aegi_keyframes = videoinfo[\"keyframes\"]\n\n# Uncomment this line to make Aegisub look for a keyframes file for the video, or ask to detect keyframes on scene changes if no file was found.\n# You can also change the GenKeyframesMode. Valid values are NEVER, ALWAYS, and ASK.\n#__aegi_keyframes = a.get_keyframes(filename, clip, __aegi_keyframes, generate=a.GenKeyframesMode.ASK)\n\n# Check if the file has an audio track. This requires the `bas` plugin.\n__aegi_hasaudio = 1 if a.check_audio(filename) else 0"
 			}
 		}
 	},