Fix a regression in the FrameMapper audio mapping code, which acciden…

src/FrameMapper.cpp

@@ -558,12 +558,12 @@ std::shared_ptr<Frame> FrameMapper::GetFrame(int64_t requested_frame)
 				frame->AddImage(std::make_shared<QImage>(*even_frame->GetImage()), false);
 		}
 
-		// Determine if the wrapped reader actually supplied audio on this frame.
-		// Video-only readers can still be mapped onto an audio-enabled timeline,
-		// which yields frames with default audio metadata but no sample data.
-		const bool reader_has_audio = mapped_frame->SampleRate() > 0 &&
-			mapped_frame->GetAudioChannelsCount() > 0 &&
-			mapped_frame->GetAudioSamplesCount() > 0;
+		// Only treat the reader as audio-capable when the wrapped reader reports
+		// audio. Individual source frames can still be empty near boundaries, but
+		// those cases should pad with silence instead of dropping this mapped frame.
+		const bool reader_has_audio = reader->info.has_audio &&
+			mapped_frame->SampleRate() > 0 &&
+			mapped_frame->GetAudioChannelsCount() > 0;
 
 		// Resample audio on frame (if needed)
 		bool need_resampling = false;
@@ -604,6 +604,10 @@ std::shared_ptr<Frame> FrameMapper::GetFrame(int64_t requested_frame)
 			}
 		}
 
+		// Preserve the target frame duration even when a source frame has no samples.
+		if (reader_has_audio && samples_in_frame > 0)
+			frame->AddAudioSilence(samples_in_frame);
+
 		// Copy the samples
 		int samples_copied = 0;
 		int64_t starting_frame = copy_samples.frame_start;
@@ -620,40 +624,45 @@ std::shared_ptr<Frame> FrameMapper::GetFrame(int64_t requested_frame)
 			}
 
 			int original_samples = original_frame->GetAudioSamplesCount();
-			if (original_samples <= 0)
-				break;
+			if (original_samples <= 0) {
+				if (starting_frame >= copy_samples.frame_end)
+					break;
+				starting_frame++;
+				continue;
+			}
+
+			if (starting_frame == copy_samples.frame_start)
+				number_to_copy = original_samples - copy_samples.sample_start;
+			else if (starting_frame > copy_samples.frame_start && starting_frame < copy_samples.frame_end)
+				number_to_copy = original_samples;
+			else
+				number_to_copy = copy_samples.sample_end + 1;
+
+			if (number_to_copy <= 0) {
+				if (starting_frame >= copy_samples.frame_end)
+					break;
+				starting_frame++;
+				continue;
+			}
+			if (number_to_copy > remaining_samples)
+				number_to_copy = remaining_samples;
 
 			// Loop through each channel
 			for (int channel = 0; channel < channels_in_frame; channel++)
 			{
 				if (starting_frame == copy_samples.frame_start)
 				{
 					// Starting frame (take the ending samples)
-					number_to_copy = original_samples - copy_samples.sample_start;
-					if (number_to_copy > remaining_samples)
-						number_to_copy = remaining_samples;
-
-					// Add samples to new frame
 					frame->AddAudio(true, channel, samples_copied, original_frame->GetAudioSamples(channel) + copy_samples.sample_start, number_to_copy, 1.0);
 				}
 				else if (starting_frame > copy_samples.frame_start && starting_frame < copy_samples.frame_end)
 				{
 					// Middle frame (take all samples)
-					number_to_copy = original_samples;
-					if (number_to_copy > remaining_samples)
-						number_to_copy = remaining_samples;
-
-					// Add samples to new frame
 					frame->AddAudio(true, channel, samples_copied, original_frame->GetAudioSamples(channel), number_to_copy, 1.0);
 				}
 				else
 				{
 					// Ending frame (take the beginning samples)
-					number_to_copy = copy_samples.sample_end + 1;
-					if (number_to_copy > remaining_samples)
-						number_to_copy = remaining_samples;
-
-					// Add samples to new frame
 					frame->AddAudio(false, channel, samples_copied, original_frame->GetAudioSamples(channel), number_to_copy, 1.0);
 				}
 			}

tests/FrameMapper.cpp

@@ -62,6 +62,47 @@ TEST_CASE( "Invalid_Frame_Too_Small", "[libopenshot][framemapper]" )
 
 }
 
+TEST_CASE( "zero_sample_source_frame_preserves_mapped_audio_duration", "[libopenshot][framemapper][audio]" )
+{
+	CacheMemory cache;
+	const Fraction fps(24, 1);
+	const int sample_rate = 48000;
+	const int channels = 2;
+	const int samples_per_frame = Frame::GetSamplesPerFrame(1, fps, sample_rate, channels);
+
+	auto empty_frame = std::make_shared<Frame>(1, 1, 1, "#000000", 0, channels);
+	empty_frame->SampleRate(sample_rate);
+	empty_frame->ChannelsLayout(LAYOUT_STEREO);
+	cache.Add(empty_frame);
+
+	auto audio_frame = std::make_shared<Frame>(2, 1, 1, "#000000", samples_per_frame, channels);
+	audio_frame->SampleRate(sample_rate);
+	audio_frame->ChannelsLayout(LAYOUT_STEREO);
+	std::vector<float> samples(samples_per_frame, 0.5f);
+	for (int channel = 0; channel < channels; ++channel)
+		audio_frame->AddAudio(true, channel, 0, samples.data(), samples_per_frame, 1.0f);
+	cache.Add(audio_frame);
+
+	DummyReader reader(fps, 1, 1, sample_rate, channels, 2.0 / fps.ToDouble(), &cache);
+	reader.info.has_audio = true;
+	reader.Open();
+
+	FrameMapper map(&reader, fps, PULLDOWN_NONE, sample_rate, channels, LAYOUT_STEREO);
+	map.Open();
+
+	auto first = map.GetFrame(1);
+	CHECK(first->GetAudioSamplesCount() == samples_per_frame);
+	for (int i = 0; i < samples_per_frame; ++i)
+		CHECK(first->GetAudioSample(0, i, 1.0) == Approx(0.0f).margin(0.0001f));
+
+	auto second = map.GetFrame(2);
+	CHECK(second->GetAudioSamplesCount() == samples_per_frame);
+	CHECK(second->GetAudioSample(0, 0, 1.0) == Approx(0.5f).margin(0.0001f));
+
+	map.Close();
+	reader.Close();
+}
+
 TEST_CASE( "24_fps_to_30_fps_Pulldown_Classic", "[libopenshot][framemapper]" )
 {
 	// Create a reader
@@ -746,4 +787,4 @@ TEST_CASE( "SampleRange", "[libopenshot][framemapper]")
 	CHECK(Samples.frame_end == 10);
 	CHECK(Samples.sample_end == 1469);
 	CHECK(Samples.total == total_samples);
-}
+}