fix: produce output segment for header only VTT input

include/packager/packager.h

@@ -81,6 +81,10 @@ struct PackagingParams {
 
   /// Flag used to adjust negative CTS offset values to correct PTS < DTS
   bool cts_offset_adjustment = false;
+
+  /// Flag used as a workaround to produce output segments when the input is a
+  /// header only VTT file
+  bool webvtt_header_only_output_segment = false;
 };
 
 /// Defines a single input/output stream.

packager/live_packager.cc

@@ -433,6 +433,7 @@ Status LivePackager::PackageTimedText(const Segment& in,
   packaging_params.mp4_output_params.sequence_number = config_.segment_number;
   packaging_params.chunking_params.adjust_sample_boundaries = true;
   packaging_params.mp4_output_params.include_pssh_in_stream = false;
+  packaging_params.webvtt_header_only_output_segment = true;
 
   StreamDescriptors descriptors =
       setupStreamDescriptors(config_, callback_params, init_callback_params);

packager/live_packager_test.cc

@@ -951,7 +951,7 @@ INSTANTIATE_TEST_CASE_P(
             "audio/en/%05d.m4s", false}));
 
 TEST_F(LivePackagerBaseTest, TestPackageTimedTextHybrikComp) {
-  for (unsigned int i = 1; i < kNumSegments; i++) {
+  for (unsigned int i = 0; i < kNumSegments; i++) {
     std::string segment_num =
         absl::StrFormat("hybrik_comp/text_in/en.m3u8_%010d.vtt", i);
     std::vector<uint8_t> segment_buffer = ReadTestDataFile(segment_num);

packager/media/demuxer/demuxer.cc

@@ -203,7 +203,7 @@ Status Demuxer::InitializeParser() {
       parser_.reset(new WebMMediaParser());
       break;
     case CONTAINER_WEBVTT:
-      parser_.reset(new WebVttParser());
+      parser_.reset(new WebVttParser(webvtt_header_only_output_segment_));
       break;
     case CONTAINER_UNKNOWN: {
       const int64_t kDumpSizeLimit = 512;

packager/media/demuxer/demuxer.h

@@ -79,6 +79,11 @@ class Demuxer : public OriginHandler {
     cts_offset_adjustment_ = cts_offset_adjustment;
   }
 
+  void set_webvtt_header_only_output_segment(
+      bool webvtt_header_only_output_segment) {
+    webvtt_header_only_output_segment_ = webvtt_header_only_output_segment;
+  }
+
  protected:
   /// @name MediaHandler implementation overrides.
   /// @{
@@ -153,6 +158,9 @@ class Demuxer : public OriginHandler {
   bool dump_stream_info_ = false;
   // flag used to adjust negative CTS offset values to correct PTS < DTS
   bool cts_offset_adjustment_ = false;
+  // flag used as a workaround to generate output segment in the case of input
+  // WEBVTT with header only
+  bool webvtt_header_only_output_segment_ = false;
   Status init_event_status_;
 };
 

packager/media/formats/webvtt/webvtt_parser.cc

@@ -190,7 +190,8 @@ void ParseSettings(const std::string& id,
 
 }  // namespace
 
-WebVttParser::WebVttParser() {}
+WebVttParser::WebVttParser(bool webvtt_header_only_output_segment)
+    : webvtt_header_only_output_segment_(webvtt_header_only_output_segment) {}
 
 void WebVttParser::Init(const InitCB& init_cb,
                         const NewMediaSampleCB& new_media_sample_cb,
@@ -207,7 +208,21 @@ void WebVttParser::Init(const InitCB& init_cb,
 
 bool WebVttParser::Flush() {
   reader_.Flush();
-  return Parse();
+  const bool isOK = Parse();
+  // Handle case when Parser was initialized but stream information not filled
+  // This happens when we parse an empty webvtt file (only contains a header)
+  if (initialized_ && !stream_info_dispatched_) {
+    if (webvtt_header_only_output_segment_) {
+      // This is a workaround in the case of input VTT and output VTT (or TTML)
+      // in MP4 where we need to generate and output MP4 segment.
+      std::vector<std::string> block;
+      block.emplace_back(R"(00:00:00.000 --> 00:00:00.001)");
+      ParseCue("", block.data(), block.size());
+    } else {
+      DispatchTextStreamInfo();
+    }
+  }
+  return isOK;
 }
 
 bool WebVttParser::Parse(const uint8_t* buf, int size) {

packager/media/formats/webvtt/webvtt_parser.h

@@ -22,7 +22,7 @@ namespace media {
 // Used to parse a WebVTT source into Cues that will be sent downstream.
 class WebVttParser : public MediaParser {
  public:
-  WebVttParser();
+  WebVttParser(bool webvtt_header_only_output_segment = false);
 
   void Init(const InitCB& init_cb,
             const NewMediaSampleCB& new_media_sample_cb,
@@ -52,6 +52,7 @@ class WebVttParser : public MediaParser {
   bool saw_cue_ = false;
   bool stream_info_dispatched_ = false;
   bool initialized_ = false;
+  bool webvtt_header_only_output_segment_ = false;
 };
 
 }  // namespace media

packager/media/formats/webvtt/webvtt_parser_unittest.cc

@@ -101,7 +101,7 @@ TEST_F(WebVttParserTest, ParseOnlyHeader) {
   ASSERT_TRUE(parser_->Parse(text, sizeof(text) - 1));
   ASSERT_TRUE(parser_->Flush());
 
-  ASSERT_TRUE(streams_.empty());
+  ASSERT_FALSE(streams_.empty());
   ASSERT_TRUE(samples_.empty());
 }
 
@@ -115,7 +115,7 @@ TEST_F(WebVttParserTest, ParseHeaderWithBOM) {
   ASSERT_TRUE(parser_->Parse(text, sizeof(text) - 1));
   ASSERT_TRUE(parser_->Flush());
 
-  ASSERT_TRUE(streams_.empty());
+  ASSERT_FALSE(streams_.empty());
   ASSERT_TRUE(samples_.empty());
 }
 

packager/media/test/data/live_packager_tests/hybrik_comp/text_in/en.m3u8_0000000000.vtt

@@ -0,0 +1 @@
+WEBVTT

packager/packager.cc

@@ -464,6 +464,8 @@ Status CreateDemuxer(const StreamDescriptor& stream,
   std::shared_ptr<Demuxer> demuxer = std::make_shared<Demuxer>(stream.input);
   demuxer->set_dump_stream_info(packaging_params.test_params.dump_stream_info);
   demuxer->set_cts_offset_adjustment(packaging_params.cts_offset_adjustment);
+  demuxer->set_webvtt_header_only_output_segment(
+      packaging_params.webvtt_header_only_output_segment);
 
   if (packaging_params.decryption_params.key_provider != KeyProvider::kNone) {
     std::unique_ptr<KeySource> decryption_key_source(