diff --git a/src/async_video_provider.cpp b/src/async_video_provider.cpp
index 8a0a2dfd1..ba9cbe287 100644
--- a/src/async_video_provider.cpp
+++ b/src/async_video_provider.cpp
@@ -140,10 +140,53 @@ void AsyncVideoProvider::RequestFrame(int new_frame, double new_time) throw() {
 	});
 }
 
+bool AsyncVideoProvider::NeedUpdate(std::vector<AssDialogueBase const*> const& visible_lines) {
+	// Always need to render after a seek
+	if (single_frame != NEW_SUBS_FILE || frame_number != last_rendered)
+		return true;
+
+	// Obviously need to render if the number of visible lines has changed
+	if (visible_lines.size() != last_lines.size())
+		return true;
+
+	for (size_t i = 0; i < last_lines.size(); ++i) {
+		auto const& last = last_lines[i];
+		auto const& cur = *visible_lines[i];
+		if (last.Layer  != cur.Layer)  return true;
+		if (last.Margin != cur.Margin) return true;
+		if (last.Style  != cur.Style)  return true;
+		if (last.Effect != cur.Effect) return true;
+		if (last.Text   != cur.Text)   return true;
+
+		// Changing the start/end time effects the appearance only if the
+		// line is animated. This is obviously not a very accurate check for
+		// animated lines, but false positives aren't the end of the world
+		if ((last.Start != cur.Start || last.End != cur.End) &&
+			(!cur.Effect.get().empty() || cur.Text.get().find('\\') != std::string::npos))
+			return true;
+	}
+
+	return false;
+}
+
 void AsyncVideoProvider::ProcAsync(uint_fast32_t req_version) {
 	// Only actually produce the frame if there's no queued changes waiting
 	if (req_version < version || frame_number < 0) return;
 
+	std::vector<AssDialogueBase const*> visible_lines;
+	for (auto const& line : subs->Events) {
+		if (!line.Comment && !(line.Start > time || line.End <= time))
+			visible_lines.push_back(&line);
+	}
+
+	if (!NeedUpdate(visible_lines)) return;
+
+	last_lines.clear();
+	last_lines.reserve(visible_lines.size());
+	for (auto line : visible_lines)
+		last_lines.push_back(*line);
+	last_rendered = frame_number;
+
 	try {
 		FrameReadyEvent *evt = new FrameReadyEvent(ProcFrame(frame_number, time), time);
 		evt->SetEventType(EVT_FRAME_READY);
diff --git a/src/async_video_provider.h b/src/async_video_provider.h
index 37232b978..c77a2664c 100644
--- a/src/async_video_provider.h
+++ b/src/async_video_provider.h
@@ -29,6 +29,7 @@ class AssFile;
 class SubtitlesProvider;
 class VideoProvider;
 class VideoProviderError;
+struct AssDialogueBase;
 struct VideoFrame;
 namespace agi {
 	class BackgroundRunner;
@@ -58,6 +59,14 @@ class AsyncVideoProvider {
 	/// currently loaded file is out of date.
 	int single_frame = -1;
 
+	/// Last rendered frame number
+	int last_rendered = -1;
+	/// Last rendered subtitles on that frame
+	std::vector<AssDialogueBase> last_lines;
+	/// Check if we actually need to honor a frame request or if no visible
+	/// lines have actually changed
+	bool NeedUpdate(std::vector<AssDialogueBase const*> const& visible_lines);
+
 	std::shared_ptr<VideoFrame> ProcFrame(int frame, double time, bool raw = false);
 
 	/// Produce a frame if req_version is still the current version