Deprecate availability_time_offset MPD flag

'availability_time_offset' is not an attribute in MPD specification,
but used to calculate availability_start_time to adjust segment
availability time. A similar effect can be achieved with standard
blessed suggested_presentation_delay flag.

If suggested_presentation_delay is not set, player is expected to
choose a suitable value.

Change-Id: I1d540bd4347b4f04b6cc5ec0778e1a5392009b09

docs/design.md

@@ -81,10 +81,6 @@ mpd_options.min_buffer_time = 5.0;
 
 // The below options are for live profile only.
 
-// Offset with respect to the wall clock time for MPD availabilityStartTime
-// and availabilityEndTime values, in seconds.
-mpd_options.availability_time_offset = 10.0;
-
 // Indicates to the player how often to refresh the media presentations, in
 // seconds.
 mpd_options.minimum_update_period = 5.0;
@@ -93,7 +89,7 @@ mpd_options.minimum_update_period = 5.0;
 mpd_options.time_shift_buffer_depth = 1800.0;
 
 // Specifies a delay, in seconds, to be added to the media presentation time.
-mpd_options.suggested_presentation_delay = 0.0;
+mpd_options.suggested_presentation_delay = 10.0;
 ```
 
 Using MpdBuilder Instance

packager/app/mpd_flags.cc

@@ -33,11 +33,6 @@ DEFINE_double(min_buffer_time,
               2.0,
               "Specifies, in seconds, a common duration used in the definition "
               "of the MPD Representation data rate.");
-DEFINE_double(availability_time_offset,
-              10.0,
-              "Offset with respect to the wall clock time for MPD "
-              "availabilityStartTime and availabilityEndTime values, in "
-              " seconds. This value is used for live profile only.");
 DEFINE_double(minimum_update_period,
               5.0,
               "Indicates to the player how often to refresh the media "

packager/app/mpd_flags.h

@@ -15,7 +15,6 @@ DECLARE_bool(generate_static_mpd);
 DECLARE_bool(output_media_info);
 DECLARE_string(mpd_output);
 DECLARE_string(base_urls);
-DECLARE_double(availability_time_offset);
 DECLARE_double(minimum_update_period);
 DECLARE_double(min_buffer_time);
 DECLARE_double(time_shift_buffer_depth);

packager/app/packager_util.cc

@@ -216,7 +216,6 @@ MpdOptions GetMpdOptions(bool on_demand_profile) {
   mpd_options.mpd_type = (on_demand_profile || FLAGS_generate_static_mpd)
                              ? MpdType::kStatic
                              : MpdType::kDynamic;
-  mpd_options.availability_time_offset = FLAGS_availability_time_offset;
   mpd_options.minimum_update_period = FLAGS_minimum_update_period;
   mpd_options.min_buffer_time = FLAGS_min_buffer_time;
   mpd_options.time_shift_buffer_depth = FLAGS_time_shift_buffer_depth;

packager/app/retired_flags.cc

@@ -16,6 +16,10 @@ DEFINE_bool(single_segment, true, "This flag is deprecated. Do not use.");
 DEFINE_bool(webm_subsample_encryption,
             true,
             "This flag is deprecated. Use vp9_subsample_encryption instead.");
+DEFINE_double(availability_time_offset,
+              10.0,
+              "This flag is deprecated. Use suggested_presentation_delay "
+              "instead which can achieve similar effect.");
 
 // The current gflags library does not provide a way to check whether a flag is
 // set in command line. If a flag has a different value to its default value,
@@ -33,6 +37,13 @@ bool InformRetiredDefaultTrueFlag(const char* flagname, bool value) {
   return true;
 }
 
+bool InformRetiredDefaultDoubleFlag(const char* flagname, double value) {
+  if (value != 0)
+    fprintf(stderr, "WARNING: %s is deprecated and ignored.\n", flagname);
+  return true;
+}
+
 DEFINE_validator(profile, &InformRetiredStringFlag);
 DEFINE_validator(single_segment, &InformRetiredDefaultTrueFlag);
 DEFINE_validator(webm_subsample_encryption, &InformRetiredDefaultTrueFlag);
+DEFINE_validator(availability_time_offset, &InformRetiredDefaultDoubleFlag);

packager/app/retired_flags.h

@@ -9,3 +9,4 @@
 DECLARE_string(profile);
 DECLARE_bool(single_segment);
 DECLARE_bool(webm_subsample_encryption);
+DECLARE_double(availability_time_offset);

packager/mpd/base/mpd_builder.cc

@@ -575,10 +575,8 @@ void MpdBuilder::AddDynamicMpdInfo(XmlNode* mpd_node) {
   if (availability_start_time_.empty()) {
     double earliest_presentation_time;
     if (GetEarliestTimestamp(&earliest_presentation_time)) {
-      availability_start_time_ =
-          XmlDateTimeNowWithOffset(mpd_options_.availability_time_offset -
-                                       std::ceil(earliest_presentation_time),
-                                   clock_.get());
+      availability_start_time_ = XmlDateTimeNowWithOffset(
+          -std::ceil(earliest_presentation_time), clock_.get());
     } else {
       LOG(ERROR) << "Could not determine the earliest segment presentation "
                     "time for availabilityStartTime calculation.";

packager/mpd/base/mpd_options.h

@@ -23,7 +23,6 @@ enum class MpdType { kStatic, kDynamic };
 struct MpdOptions {
   DashProfile dash_profile = DashProfile::kOnDemand;
   MpdType mpd_type = MpdType::kStatic;
-  double availability_time_offset = 0;
   double minimum_update_period = 0;
   // TODO(tinskip): Set min_buffer_time in unit tests rather than here.
   double min_buffer_time = 2.0;