Preserve audio-only reader dimensions on pasted clips

-Set the parent timeline before hydrating clips inserted through JSON diffs, matching full project JSON load behavior. This lets copied/pasted clips expose timeline context while their nested readers are rebuilt.
-Avoid clobbering valid stored dimensions for audio-only FFmpeg readers with the 720x480 fallback. The fallback is now only used when width or height are missing, while parent timeline preview dimensions can still override when available.
-Add regression coverage for audio-only FFmpegReader JSON hydration and timeline JSON-diff insertion preserving 1280x720 dimensions.

src/FFmpegReader.cpp

@@ -1000,8 +1000,10 @@ void FFmpegReader::UpdateAudioInfo() {
 		info.fps.den = 1;
 		info.video_timebase.num = 1;
 		info.video_timebase.den = 30;
-		info.width = 720;
-		info.height = 480;
+		if (info.width <= 0 || info.height <= 0) {
+			info.width = 720;
+			info.height = 480;
+		}
 
 		// Use timeline to set correct width & height (if any)
 		Clip *parent = static_cast<Clip *>(ParentClip());

src/Timeline.cpp

@@ -1486,6 +1486,10 @@ void Timeline::apply_json_to_clips(Json::Value change) {
 		// Keep track of allocated clip objects
 		allocated_clips.insert(clip);
 
+		// Match full timeline JSON loading: parent timeline must be available
+		// before clip JSON can inflate nested readers/effects.
+		clip->ParentTimeline(this);
+
 		// Set properties of clip from JSON
 		clip->SetJsonValue(change["value"]);
 

tests/FFmpegReader.cpp

@@ -143,6 +143,36 @@ TEST_CASE( "Check_Audio_File", "[libopenshot][ffmpegreader]" )
 	r.Close();
 }
 
+TEST_CASE( "Audio_Only_SetJson_Preserves_Stored_Dimensions", "[libopenshot][ffmpegreader][json]" )
+{
+	std::stringstream path;
+	path << TEST_MEDIA_PATH << "piano.wav";
+
+	FFmpegReader r(path.str());
+	std::stringstream json;
+	json << "{\"type\":\"FFmpegReader\","
+		<< "\"path\":\"" << path.str() << "\","
+		<< "\"has_audio\":true,"
+		<< "\"has_video\":false,"
+		<< "\"width\":1280,"
+		<< "\"height\":720,"
+		<< "\"fps\":{\"num\":30,\"den\":1},"
+		<< "\"sample_rate\":44100,"
+		<< "\"channels\":2,"
+		<< "\"channel_layout\":3,"
+		<< "\"duration\":1.0}";
+
+	r.SetJson(json.str());
+	r.Open();
+
+	CHECK(r.info.has_audio);
+	CHECK_FALSE(r.info.has_video);
+	CHECK(r.info.width == 1280);
+	CHECK(r.info.height == 720);
+	CHECK(r.GetFrame(1)->GetWidth() == 1280);
+	CHECK(r.GetFrame(1)->GetHeight() == 720);
+}
+
 TEST_CASE( "Check_Video_File", "[libopenshot][ffmpegreader]" )
 {
 	// Create a reader

tests/Timeline.cpp

@@ -480,6 +480,48 @@ TEST_CASE("ReaderInfo constructor", "[libopenshot][timeline]")
 	CHECK(r1->info.channel_layout == t1.info.channel_layout);
 }
 
+TEST_CASE("JSON diff insert keeps audio-only clip at stored timeline dimensions", "[libopenshot][timeline][json]")
+{
+	std::stringstream path;
+	path << TEST_MEDIA_PATH << "piano.wav";
+
+	Timeline t(1280, 720, Fraction(30, 1), 44100, 2, LAYOUT_STEREO);
+	std::stringstream diff;
+	diff << "[{\"type\":\"insert\",\"key\":[\"clips\"],\"value\":{"
+		<< "\"id\":\"audio-copy\","
+		<< "\"position\":0,"
+		<< "\"start\":0,"
+		<< "\"end\":1,"
+		<< "\"duration\":1,"
+		<< "\"layer\":1,"
+		<< "\"reader\":{\"type\":\"FFmpegReader\","
+		<< "\"path\":\"" << path.str() << "\","
+		<< "\"has_audio\":true,"
+		<< "\"has_video\":false,"
+		<< "\"width\":1280,"
+		<< "\"height\":720,"
+		<< "\"fps\":{\"num\":30,\"den\":1},"
+		<< "\"sample_rate\":44100,"
+		<< "\"channels\":2,"
+		<< "\"channel_layout\":3,"
+		<< "\"duration\":1.0}"
+		<< "}}]";
+
+	t.ApplyJsonDiff(diff.str());
+
+	std::list<Clip*> clips = t.Clips();
+	REQUIRE(clips.size() == 1);
+	Clip* clip = clips.front();
+	CHECK(clip->ParentTimeline() == &t);
+	CHECK(clip->Reader()->info.width == 1280);
+	CHECK(clip->Reader()->info.height == 720);
+
+	std::shared_ptr<Frame> frame = t.GetFrame(1);
+	REQUIRE(frame);
+	CHECK(frame->GetWidth() == 1280);
+	CHECK(frame->GetHeight() == 720);
+}
+
 TEST_CASE( "width and height functions", "[libopenshot][timeline]" )
 {
 	Fraction fps(30000,1000);