AV1: require manual activation via `--engage enable_av1`; fail otherwise

Reason: the AV1 bitstream specification hasn't been finalized yet.

NEWS.md

@@ -56,6 +56,12 @@
   MXE is now supported by setting `configure`'s `host` triplet accordingly,
   e.g. `--host=x86_64-w64-mingw32.shared`.
 
+## Other changes
+
+* mkvmerge: AV1: support for AV1 must be activated manually by adding
+  `--engage enable_av1` as the AV1 bitstream specification hasn't been
+  finalized yet.
+
 
 # Version 22.0.0 "At The End Of The World" 2018-04-01
 

src/common/hacks.cpp

@@ -48,6 +48,7 @@ get_list() {
       "keep_last_chapter_in_mpls",
       "keep_track_statistics_tags",
       "all_i_slices_are_key_frames",
+      "enable_av1",
     };
   }
 

src/common/hacks.h

@@ -43,7 +43,8 @@ constexpr unsigned int NO_DELAY_FOR_GARBAGE_IN_AVI  = 18;
 constexpr unsigned int KEEP_LAST_CHAPTER_IN_MPLS    = 19;
 constexpr unsigned int KEEP_TRACK_STATISTICS_TAGS   = 20;
 constexpr unsigned int ALL_I_SLICES_ARE_KEY_FRAMES  = 21;
-constexpr unsigned int MAX_IDX                      = 21;
+constexpr unsigned int ENABLE_AV1                   = 22;
+constexpr unsigned int MAX_IDX                      = 22;
 }
 
 void engage(const std::string &hacks);

src/mkvtoolnix-gui/merge/additional_command_line_options_dialog.cpp

@@ -85,6 +85,7 @@ AdditionalCommandLineOptionsDialog::AdditionalCommandLineOptionsDialog(QWidget *
   add(Q("--engage all_i_slices_are_key_frames"),  false, hacks,
       { QY("Some h.264/AVC tracks contain I slices but lack real key frames."),
         QY("This option forces mkvmerge to treat all of those I slices as key frames.") });
+  add(Q("--engage enable_av1"),                   false, hacks, { QY("Enables AV1 video support even though the AV1 bitstream specification hasn't been finalized yet.") });
   add(Q("--engage cow"),                          false, hacks, { QY("No help available.") });
 
   m_ui->gbGlobalOutputControl->layout()->addItem(new QSpacerItem(0, 0, QSizePolicy::Minimum, QSizePolicy::Expanding));

src/output/p_av1.cpp

@@ -15,6 +15,7 @@
 
 #include "common/av1.h"
 #include "common/codec.h"
+#include "common/hacks.h"
 #include "merge/connection_checks.h"
 #include "output/p_av1.h"
 
@@ -24,6 +25,9 @@ av1_video_packetizer_c::av1_video_packetizer_c(generic_reader_c *p_reader,
                                                track_info_c &p_ti)
   : generic_packetizer_c{p_reader, p_ti}
 {
+  if (!mtx::hacks::is_engaged(mtx::hacks::ENABLE_AV1))
+    mxerror(Y("Support for AV1 is currently experimental and must be enabled with '--engage enable_av1' as the AV1 bitstream specification hasn't been finalized yet.\n"));
+
   m_timestamp_factory_application_mode = TFA_SHORT_QUEUEING;
 
   set_track_type(track_video);

tests/test-638av1_ivf_webm.rb

@@ -5,8 +5,8 @@ describe "mkvmerge / reading AV1 from IVF, WebM; writing Matroska, WebM"
 
 base = "data/av1/av1."
 
-test_merge "#{base}ivf"
-test_merge "#{base}webm"
+test_merge "#{base}ivf",  :args => "--engage enable_av1"
+test_merge "#{base}webm", :args => "--engage enable_av1"
 
-test_merge "#{base}ivf",  :args => "--webm"
-test_merge "#{base}webm", :args => "--webm"
+test_merge "#{base}ivf",  :args => "--engage enable_av1 --webm"
+test_merge "#{base}webm", :args => "--engage enable_av1 --webm"