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(