Re-add AC3/EAC3 audio demuxing support

media/ffmpeg/ffmpeg_common.cc

Index: media/ffmpeg/ffmpeg_common.cc
diff --git a/media/ffmpeg/ffmpeg_common.cc b/media/ffmpeg/ffmpeg_common.cc
index 3d3a8b89957d36be73c1480b1a63788dee3049d9..b65ceddeb0fd17185f15843196e3feda31fe6d26 100644
--- a/media/ffmpeg/ffmpeg_common.cc
+++ b/media/ffmpeg/ffmpeg_common.cc
@@ -14,6 +14,7 @@
 #include "media/base/decoder_buffer.h"
 #include "media/base/video_decoder_config.h"
 #include "media/base/video_util.h"
+#include "media/media_features.h"
 
 namespace media {
 
@@ -67,6 +68,12 @@ static AudioCodec CodecIDToAudioCodec(AVCodecID codec_id) {
   switch (codec_id) {
     case AV_CODEC_ID_AAC:
       return kCodecAAC;
+#if BUILDFLAG(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    case AV_CODEC_ID_AC3:
+      return kCodecAC3;
+    case AV_CODEC_ID_EAC3:
+      return kCodecEAC3;
+#endif
     case AV_CODEC_ID_MP3:
       return kCodecMP3;
     case AV_CODEC_ID_VORBIS:
@@ -309,18 +316,37 @@ bool AVCodecContextToAudioDecoderConfig(const AVCodecContext* codec_context,
       codec_context->channel_layout, codec_context->channels);
 
   int sample_rate = codec_context->sample_rate;
-  if (codec == kCodecOpus) {
-    // |codec_context->sample_fmt| is not set by FFmpeg because Opus decoding is
-    // not enabled in FFmpeg.  It doesn't matter what value is set here, so long
-    // as it's valid, the true sample format is selected inside the decoder.
-    sample_format = kSampleFormatF32;
-
-    // Always use 48kHz for OPUS.  Technically we should match to the highest
-    // supported hardware sample rate among [8, 12, 16, 24, 48] kHz, but we
-    // don't know the hardware sample rate at this point and those rates are
-    // rarely used for output.  See the "Input Sample Rate" section of the spec:
-    // http://tools.ietf.org/html/draft-terriberry-oggopus-01#page-11
-    sample_rate = 48000;
+  switch (codec) {
+    case kCodecOpus:
+      // |codec_context->sample_fmt| is not set by FFmpeg because Opus decoding
+      // is not enabled in FFmpeg.  It doesn't matter what value is set here, so
+      // long as it's valid, the true sample format is selected inside the
+      // decoder.
+      sample_format = kSampleFormatF32;
+
+      // Always use 48kHz for OPUS.  Technically we should match to the highest
+      // supported hardware sample rate among [8, 12, 16, 24, 48] kHz, but we
+      // don't know the hardware sample rate at this point and those rates are
+      // rarely used for output.  See the "Input Sample Rate" section of the
+      // spec: http://tools.ietf.org/html/draft-terriberry-oggopus-01#page-11
+      sample_rate = 48000;
+      break;
+
+    // For AC3/EAC3 we enable only demuxing, but not decoding, so FFmpeg does
+    // not fill |sample_fmt|.
+    case kCodecAC3:
+    case kCodecEAC3:
+#if BUILDFLAG(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+      // The spec for AC3/EAC3 audio is ETSI TS 102 366. According to sections
+      // F.3.1 and F.5.1 in that spec the sample_format for AC3/EAC3 must be 16.
+      sample_format = kSampleFormatS16;
+#else
+      NOTREACHED();
+#endif
+      break;
+
+    default:
+      break;
   }
 
   base::TimeDelta seek_preroll;
@@ -353,9 +379,19 @@ bool AVCodecContextToAudioDecoderConfig(const AVCodecContext* codec_context,
                      seek_preroll,
                      codec_context->delay);
 
-  if (codec != kCodecOpus) {
-    DCHECK_EQ(av_get_bytes_per_sample(codec_context->sample_fmt) * 8,
-              config->bits_per_channel());
+  // Verify that AudioConfig.bits_per_channel was calculated correctly for
+  // codecs that have |sample_fmt| set by FFmpeg.
+  switch (codec) {
+    case kCodecOpus:
+#if BUILDFLAG(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    case kCodecAC3:
+    case kCodecEAC3:
+#endif
+      break;
+    default:
+      DCHECK_EQ(av_get_bytes_per_sample(codec_context->sample_fmt) * 8,
+                config->bits_per_channel());
+      break;
   }
 
   return true;