Re-add AC3/EAC3 audio demuxing support

media/media_options.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chromecast_build.gni")
+import("//build/config/features.gni")
 import("//build/config/headless_build.gni")
 
 declare_args() {
   # Allows distributions to link pulseaudio directly (DT_NEEDED) instead of
   # using dlopen. This helps with automated detection of ABI mismatches and
   # prevents silent errors.
   link_pulseaudio = false
 
   # Enable usage of FFmpeg within the media library. Used for most software
   # based decoding, demuxing, and sometimes optimized FFTs. If disabled,
@@ skipping 25 matching lines @@
       (!is_chromecast || is_cast_desktop_build)) {
     use_alsa = true
     if (!use_cras) {
       use_pulseaudio = true
     }
   }
 
   # Use low-memory buffers on non-Android builds of Chromecast.
   use_low_memory_buffer = is_chromecast && !is_android
 
-  enable_mse_mpeg2ts_stream_parser = is_chromecast
+  # Enables AC3/EAC3 audio demuxing. This is enabled only on Chromecast, since
+  # it only provides demuxing, and is only useful for AC3/EAC3 audio
+  # pass-through to HDMI sink on Chromecast.
+  enable_ac3_eac3_audio_demuxing = proprietary_codecs && is_chromecast
+
+  enable_mse_mpeg2ts_stream_parser = proprietary_codecs && is_chromecast
 
   # Enable HEVC/H265 demuxing. Actual decoding must be provided by the
   # platform. Enable by default for Chromecast.
   enable_hevc_demuxing = is_chromecast
 
   # Experiment to enable mojo media application: http://crbug.com/431776
   # Valid options are:
   # - "none": Do not use mojo media application.
   # - "browser": Use mojo media application hosted in the browser process.
   # - "gpu": Use mojo media application hosted in the gpu process.
   # - "utility": Use mojo media application hosted in the utility process.
   enable_mojo_media = "none"
 
   # TODO(GYP): This should be a platform define.
   is_openbsd = false
 }