diff --git a/packager/app/stream_descriptor.cc b/packager/app/stream_descriptor.cc
index 715e55d30d7..daca20b7032 100644
--- a/packager/app/stream_descriptor.cc
+++ b/packager/app/stream_descriptor.cc
@@ -36,6 +36,7 @@ enum FieldType {
   kDashRolesField,
   kDashOnlyField,
   kHlsOnlyField,
+  kInputFormatField,
 };
 
 struct FieldNameToTypeMapping {
@@ -83,6 +84,7 @@ const FieldNameToTypeMapping kFieldNameTypeMappings[] = {
     {"role", kDashRolesField},
     {"dash_only", kDashOnlyField},
     {"hls_only", kHlsOnlyField},
+    {"input_format", kInputFormatField},
 };
 
 FieldType GetFieldType(const std::string& field_name) {
@@ -247,6 +249,10 @@ base::Optional<StreamDescriptor> ParseStreamDescriptor(
         }
         descriptor.hls_only = hls_only_value > 0;
         break;
+      case kInputFormatField: {
+        descriptor.input_format = iter->second;
+        break;
+      }
       default:
         LOG(ERROR) << "Unknown field in stream descriptor (\"" << iter->first
                    << "\").";
diff --git a/packager/media/demuxer/demuxer.cc b/packager/media/demuxer/demuxer.cc
index 10e69a01555..0d7c659c3f1 100644
--- a/packager/media/demuxer/demuxer.cc
+++ b/packager/media/demuxer/demuxer.cc
@@ -160,18 +160,22 @@ Status Demuxer::InitializeParser() {
                   "Cannot open file for reading " + file_name_);
   }
 
-  // Read enough bytes before detecting the container.
   int64_t bytes_read = 0;
-  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)
-      break;
-    bytes_read += read_result;
+  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)
+        break;
+      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_) {
diff --git a/packager/media/demuxer/demuxer.h b/packager/media/demuxer/demuxer.h
index 5a5aaa4c89a..4d089ead7d5 100644
--- a/packager/media/demuxer/demuxer.h
+++ b/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
diff --git a/packager/media/event/muxer_listener_factory.h b/packager/media/event/muxer_listener_factory.h
index fd7e384fdcf..86ac9e08692 100644
--- a/packager/media/event/muxer_listener_factory.h
+++ b/packager/media/event/muxer_listener_factory.h
@@ -53,6 +53,8 @@ class MuxerListenerFactory {
     std::vector<std::string> dash_accessiblities;
     std::vector<std::string> dash_roles;
     bool dash_only = false;
+
+    std::string input_format;
   };
 
   /// Create a new muxer listener.
diff --git a/packager/media/formats/webvtt/webvtt_parser.cc b/packager/media/formats/webvtt/webvtt_parser.cc
index 197a05bb722..03e5fd418d9 100644
--- a/packager/media/formats/webvtt/webvtt_parser.cc
+++ b/packager/media/formats/webvtt/webvtt_parser.cc
@@ -223,14 +223,12 @@ 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;
   }
diff --git a/packager/packager.cc b/packager/packager.cc
index 25a3d14f078..ac6bdbb7aa5 100644
--- a/packager/packager.cc
+++ b/packager/packager.cc
@@ -84,6 +84,8 @@ MuxerListenerFactory::StreamData ToMuxerListenerData(
   data.dash_accessiblities = stream.dash_accessiblities;
   data.dash_roles = stream.dash_roles;
   data.dash_only = stream.dash_only;
+
+  data.input_format = stream.input_format;
   return data;
 };
 
@@ -471,6 +473,7 @@ 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(
diff --git a/packager/packager.h b/packager/packager.h
index 38494853ef7..35ecb10c032 100644
--- a/packager/packager.h
+++ b/packager/packager.h
@@ -140,6 +140,11 @@ struct StreamDescriptor {
   bool dash_only = false;
   /// 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;
 };
 
 class SHAKA_EXPORT Packager {