Improve VTT playlist duration precision in (LL-)HLS

Author: getroot

src/projects/modules/containers/webvtt/webvtt_packager.cpp

@@ -37,7 +37,7 @@ namespace webvtt
 		return true;
 	}
 
-	bool Packager::MakeSegment(int64_t segment_number, int64_t start_time_ms, int64_t duration_ms)
+	bool Packager::MakeSegment(int64_t segment_number, int64_t start_time_ms, double duration_ms)
 	{
 		ov::String vtt_text;
 
@@ -62,7 +62,7 @@ namespace webvtt
 		return true;
 	}
 
-	bool Packager::MakePartialSegment(int64_t segment_number, int64_t partial_segment_number, int64_t start_time_ms, int64_t duration_ms)
+	bool Packager::MakePartialSegment(int64_t segment_number, int64_t partial_segment_number, int64_t start_time_ms, double duration_ms)
 	{
 		ov::String vtt_text;
 
@@ -103,10 +103,10 @@ namespace webvtt
 		return vtt_text;
 	}
 
-	const ov::String Packager::MakeCueText(int64_t start_time_ms, int64_t duration_ms, bool remove_used_frames)
+	const ov::String Packager::MakeCueText(int64_t start_time_ms, double duration_ms, bool remove_used_frames)
 	{
 		ov::String cue_text;
-		int64_t end_time_ms = start_time_ms + duration_ms;
+		int64_t end_time_ms = start_time_ms + static_cast<int64_t>(llround(duration_ms));
 		bool expired_frame = false;
 		std::unique_lock<std::shared_mutex> lock(_frames_guard);
 		for (auto it = _frames.begin(); it != _frames.end();)

src/projects/modules/containers/webvtt/webvtt_packager.h

@@ -172,8 +172,8 @@ namespace webvtt
 
 		bool AddFrame(const std::shared_ptr<WebVTTFrame> &frame);
 
-		bool MakeSegment(int64_t segment_number, int64_t start_time_ms, int64_t duration_ms);
-		bool MakePartialSegment(int64_t segment_number, int64_t partial_segment_number, int64_t start_time_ms, int64_t duration_ms);
+		bool MakeSegment(int64_t segment_number, int64_t start_time_ms, double duration_ms);
+		bool MakePartialSegment(int64_t segment_number, int64_t partial_segment_number, int64_t start_time_ms, double duration_ms);
 		bool DeleteSegment(int64_t segment_number);
 
 		// SegmentStorage overrides
@@ -193,7 +193,7 @@ namespace webvtt
 		std::shared_ptr<PartialSegment> GetPartialSegmentInternal(int64_t segment_number, int64_t partial_segment_number) const;
 
 		const ov::String MakeVTTHeader(int64_t start_time_ms);
-		const ov::String MakeCueText(int64_t start_time_ms, int64_t duration_ms, bool remove_used_frames);
+		const ov::String MakeCueText(int64_t start_time_ms, double duration_ms, bool remove_used_frames);
 
 		// start_time_ms : frame
 		// To make ordered

src/projects/publishers/llhls/llhls_stream.cpp

@@ -167,6 +167,10 @@ bool LLHlsStream::Start()
 	auto data_track = GetFirstTrackByType(cmn::MediaType::Data);
 
 	std::shared_ptr<MediaTrack> first_video_track = nullptr, first_audio_track = nullptr;
+	first_video_track = GetFirstTrackByType(cmn::MediaType::Video);
+    first_audio_track = GetFirstTrackByType(cmn::MediaType::Audio);
+
+	_vtt_reference_track_id = first_video_track ? first_video_track->GetId() : first_audio_track ? first_audio_track->GetId() : -1;
 	for (const auto &[id, track] : _tracks)
 	{
 		if (IsSupportedMediaCodec(track->GetCodecId()) == true)
@@ -176,16 +180,6 @@ bool LLHlsStream::Start()
 				logte("LLHlsStream(%s/%s) - Failed to add packager for track(%u)", GetApplication()->GetVHostAppName().CStr(), GetName().CStr(), track->GetId());
 				return false;
 			}
-
-			// For default llhls.m3u8
-			if (first_video_track == nullptr && track->GetMediaType() == cmn::MediaType::Video)
-			{
-				first_video_track = track;
-			}
-			else if (first_audio_track == nullptr && track->GetMediaType() == cmn::MediaType::Audio)
-			{
-				first_audio_track = track;
-			}
 		}
 		else
 		{
@@ -199,8 +193,6 @@ bool LLHlsStream::Start()
 		}
 	}
 
-	_vtt_reference_track_id = first_video_track ? first_video_track->GetId() : first_audio_track ? first_audio_track->GetId() : -1;
-
 	// Set renditions to each chunklist writer
 	{
 		std::lock_guard<std::shared_mutex> lock(_chunklist_map_lock);
@@ -1524,6 +1516,11 @@ bool LLHlsStream::AddVttPackager(const std::shared_ptr<const MediaTrack> &track)
 	// Chunklist
 	auto segment_duration = std::round(static_cast<double>(_storage_config.segment_duration_ms) / 1000.0);
 	auto chunk_duration = static_cast<double>(_packager_config.chunk_duration_ms) / 1000.0;
+	auto refer_track = GetTrack(_vtt_reference_track_id);
+	if (refer_track != nullptr)
+	{
+		chunk_duration = std::round(ComputeOptimalPartDuration(refer_track)) / 1000.0;
+	}
 
 	auto chunklist = std::make_shared<LLHlsChunklist>(GetChunklistName(track->GetId()),
 													  track,