feat: Allow LIVE UDP WebVTT input

docs/source/options/stream_descriptors.rst

@@ -60,6 +60,20 @@ These are the available fields:
     For subtitles in MP4, you can specify 'vtt+mp4' or 'ttml+mp4' to control
     which text format is used.
 
+:input_format (format):
+
+    Optional value which specifies the format of the input files or
+    streams. If not specified, it will be autodetected, which in some
+    cases may fail.
+
+    For example, a live UDP WebVTT input stream may be up and streaming
+    long before a shaka packager instance consumes it, and therefore
+    shaka packager never gets the initial "WEBVTT" header string. In
+    such a case, shaka packager can't properly autodetect the stream
+    format as WebVTT, and thus doesn't process it. But stating
+    'input_format=webvtt' as selector parameter will tell shaka packager
+    to omit autodetection and consider WebVTT format for that stream.
+
 :trick_play_factor (tpf):
 
     Optional value which specifies the trick play, a.k.a. trick mode, stream

include/packager/packager.h

@@ -152,6 +152,11 @@ struct StreamDescriptor {
   /// Set to true to indicate that the stream is for hls only.
   bool hls_only = false;
 
+  /// Optional value which specifies input container format.
+  /// Useful for live streaming situations, like auto-detecting webvtt without
+  /// its initial header.
+  std::string input_format;
+
   /// Optional, indicates if this is a Forced Narrative subtitle stream.
   bool forced_subtitle = false;
 

packager/app/packager_main.cc

@@ -89,6 +89,10 @@ const char kUsage[] =
     "  - output_format (format): Optional value which specifies the format\n"
     "    of the output files (MP4 or WebM).  If not specified, it will be\n"
     "    derived from the file extension of the output file.\n"
+    "  - input_format (format): Optional value which specifies the format\n"
+    "    of the input files or streams. If not specified, it will be\n"
+    "    autodetected, which in some cases (such as live UDP webvtt) may\n"
+    "    fail.\n"
     "  - skip_encryption=0|1: Optional. Defaults to 0 if not specified. If\n"
     "    it is set to 1, no encryption of the stream will be made.\n"
     "  - drm_label: Optional value for custom DRM label, which defines the\n"

packager/app/stream_descriptor.cc

@@ -41,6 +41,7 @@ enum FieldType {
   kHlsOnlyField,
   kDashLabelField,
   kForcedSubtitleField,
+  kInputFormatField,
 };
 
 struct FieldNameToTypeMapping {
@@ -90,6 +91,7 @@ const FieldNameToTypeMapping kFieldNameTypeMappings[] = {
     {"hls_only", kHlsOnlyField},
     {"dash_label", kDashLabelField},
     {"forced_subtitle", kForcedSubtitleField},
+    {"input_format", kInputFormatField},
 };
 
 FieldType GetFieldType(const std::string& field_name) {
@@ -271,6 +273,10 @@ std::optional<StreamDescriptor> ParseStreamDescriptor(
         }
         descriptor.forced_subtitle = forced_subtitle_value > 0;
         break;
+      case kInputFormatField: {
+        descriptor.input_format = pair.second;
+        break;
+      }
       default:
         LOG(ERROR) << "Unknown field in stream descriptor (\"" << pair.first
                    << "\").";

packager/media/demuxer/demuxer.cc

@@ -165,21 +165,25 @@ Status Demuxer::InitializeParser() {
                   "Cannot open file for reading " + file_name_);
   }
 
-  // Read enough bytes before detecting the container.
   int64_t bytes_read = 0;
   bool eof = false;
-  while (static_cast<size_t>(bytes_read) < kInitBufSize) {
-    int64_t read_result =
-        media_file_->Read(buffer_.get() + bytes_read, kInitBufSize);
-    if (read_result < 0)
-      return Status(error::FILE_FAILURE, "Cannot read file " + file_name_);
-    if (read_result == 0) {
-      eof = true;
-      break;
+  if (input_format_.empty()) {
+    // Read enough bytes before detecting the container.
+    while (static_cast<size_t>(bytes_read) < kInitBufSize) {
+      int64_t read_result =
+          media_file_->Read(buffer_.get() + bytes_read, kInitBufSize);
+      if (read_result < 0)
+        return Status(error::FILE_FAILURE, "Cannot read file " + file_name_);
+      if (read_result == 0) {
+        eof = true;
+        break;
+      }
+      bytes_read += read_result;
     }
-    bytes_read += read_result;
+    container_name_ = DetermineContainer(buffer_.get(), bytes_read);
+  } else {
+    container_name_ = DetermineContainerFromFormatName(input_format_);
   }
-  container_name_ = DetermineContainer(buffer_.get(), bytes_read);
 
   // Initialize media parser.
   switch (container_name_) {

packager/media/demuxer/demuxer.h

@@ -75,6 +75,10 @@ class Demuxer : public OriginHandler {
     dump_stream_info_ = dump_stream_info;
   }
 
+  void set_input_format(std::string input_format) {
+    input_format_ = input_format;
+  }
+
  protected:
   /// @name MediaHandler implementation overrides.
   /// @{
@@ -148,6 +152,8 @@ class Demuxer : public OriginHandler {
   // Whether to dump stream info when it is received.
   bool dump_stream_info_ = false;
   Status init_event_status_;
+  // Explicitly defined input format, for avoiding autodetection.
+  std::string input_format_;
 };
 
 }  // namespace media

packager/media/event/muxer_listener_factory.h

@@ -40,6 +40,10 @@ class MuxerListenerFactory {
     // told to output media info.
     std::string media_info_output;
 
+    // Explicit input format, for avoiding autodetection when needed.
+    // This is useful for cases such as live WebVTT through UDP.
+    std::string input_format;
+
     // HLS specific values needed to write to HLS manifests. Will only be used
     // if an HlsNotifier is given to the factory.
     std::string hls_group_id;

packager/media/formats/webvtt/webvtt_parser.cc

@@ -225,14 +225,12 @@ bool WebVttParser::Parse() {
     // Check the header. It is possible for a 0xFEFF BOM to come before the
     // header text.
     if (block.size() != 1) {
-      LOG(ERROR) << "Failed to read WEBVTT header - "
-                 << "block size should be 1 but was " << block.size() << ".";
-      return false;
+      LOG(WARNING) << "Failed to read WEBVTT header - "
+                   << "block size should be 1 but was " << block.size() << ".";
     }
     if (block[0] != "WEBVTT" && block[0] != "\xEF\xBB\xBFWEBVTT") {
-      LOG(ERROR) << "Failed to read WEBVTT header - should be WEBVTT but was "
-                 << block[0];
-      return false;
+      LOG(WARNING) << "Failed to read WEBVTT header - should be WEBVTT but was "
+                   << block[0];
     }
     initialized_ = true;
   }

packager/media/formats/webvtt/webvtt_parser_unittest.cc

@@ -119,14 +119,17 @@ TEST_F(WebVttParserTest, ParseHeaderWithBOM) {
   ASSERT_TRUE(samples_.empty());
 }
 
-TEST_F(WebVttParserTest, FailToParseHeaderWrongWord) {
+TEST_F(WebVttParserTest, ParseNoHeaderWithoutExiting) {
+  // A proper WebVTT file should have the "WEBVTT" string header.
+  // But UDP input (not file) may be ingested when the header already
+  // passed, and it will not be repeated later.
   const uint8_t text[] =
-      "NOT WEBVTT\n"
+      "00:00:01.000 --> 00:00:02.000\n"
       "\n";
 
   ASSERT_NO_FATAL_FAILURE(SetUpAndInitialize());
 
-  ASSERT_FALSE(parser_->Parse(text, sizeof(text) - 1));
+  ASSERT_TRUE(parser_->Parse(text, sizeof(text) - 1));
 
   ASSERT_TRUE(streams_.empty());
   ASSERT_TRUE(samples_.empty());
@@ -140,7 +143,7 @@ TEST_F(WebVttParserTest, FailToParseHeaderNotOneLine) {
 
   ASSERT_NO_FATAL_FAILURE(SetUpAndInitialize());
 
-  ASSERT_FALSE(parser_->Parse(text, sizeof(text) - 1));
+  ASSERT_TRUE(parser_->Parse(text, sizeof(text) - 1));
 
   ASSERT_TRUE(streams_.empty());
   ASSERT_TRUE(samples_.empty());

packager/packager.cc

@@ -77,6 +77,7 @@ MuxerListenerFactory::StreamData ToMuxerListenerData(
   data.dash_only = stream.dash_only;
   data.index = stream.index;
   data.dash_label = stream.dash_label;
+  data.input_format = stream.input_format;
   return data;
 };
 
@@ -463,6 +464,7 @@ Status CreateDemuxer(const StreamDescriptor& stream,
                      std::shared_ptr<Demuxer>* new_demuxer) {
   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_input_format(stream.input_format);
 
   if (packaging_params.decryption_params.key_provider != KeyProvider::kNone) {
     std::unique_ptr<KeySource> decryption_key_source(