Re-add AC3/EAC3 audio demuxing support

media/ffmpeg/ffmpeg_common.cc

 // Copyright (c) 2012 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.
 
 #include "media/ffmpeg/ffmpeg_common.h"
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/sha1.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 49 matching lines @@
 int64_t ConvertToTimeBase(const AVRational& time_base,
                           const base::TimeDelta& timestamp) {
   return av_rescale_q(timestamp.InMicroseconds(), kMicrosBase, time_base);
 }
 
 // Converts an FFmpeg audio codec ID into its corresponding supported codec id.
 static AudioCodec CodecIDToAudioCodec(AVCodecID codec_id) {
   switch (codec_id) {
     case AV_CODEC_ID_AAC:
       return kCodecAAC;
+#if defined(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:
       return kCodecVorbis;
     case AV_CODEC_ID_PCM_U8:
     case AV_CODEC_ID_PCM_S16LE:
     case AV_CODEC_ID_PCM_S24LE:
     case AV_CODEC_ID_PCM_S32LE:
     case AV_CODEC_ID_PCM_F32LE:
       return kCodecPCM;
@@ skipping 236 matching lines @@
     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;
   }
 
+  // For AC3/EAC3 we enable only demuxing, but not decoding (due to licensing

[ddorwin, 2016/01/07 19:12:43]

For a variety of reasons, including that we don't have a complex matrix of
"ffmpeg_branding" options. I think you can just drop the ().

[servolk, 2016/01/07 21:17:36]

Done.

+  // restrictions), so FFmpeg does not fill |sample_fmt|.
+  if (codec == kCodecAC3 || codec == kCodecEAC3) {

[ddorwin, 2016/01/07 19:12:43]

This should be else if.

[servolk, 2016/01/07 21:17:36]

Even if we wrap it into #if as suggested below? I think the difference between
if/'else if' in this case is really minor and I'd rather have a stand-alone
piece of code inside #if, rather than relying on another if to be above it.

+    // The spec for AC3/EAC3 audio ETSI TS 102 366, according to Sections F.3.1
+    // and F.5.1 sample_format for AC3/EAC3 must be 16.
+    sample_format = kSampleFormatS16;
+  }

[ddorwin, 2016/01/07 19:12:43]

Should this code be ifdef'd or should we have this "dead" code in all builds?

How is this different from line 70-75?

[servolk, 2016/01/07 21:17:36]

The difference is really minor, I think lines 70-75 were wrapped in #if to
guarantee CodecIDToAudioCodec never returns kCodecAC3/EAC3 for builds where
AC3/EAC3 are disabled, whereas this code would simply be dead, but harmless even
if somehow it got executed on the builds with AC3/EAC3 disabled. But I agree we
can wrap this into #if as well, it shouldn't make any difference.

+
   base::TimeDelta seek_preroll;
   if (codec_context->seek_preroll > 0) {
     seek_preroll = base::TimeDelta::FromMicroseconds(
         codec_context->seek_preroll * 1000000.0 / codec_context->sample_rate);
   }
 
   // AVStream occasionally has invalid extra data. See http://crbug.com/517163
   if ((codec_context->extradata_size == 0) !=
       (codec_context->extradata == nullptr)) {
     LOG(ERROR) << __FUNCTION__
                << (codec_context->extradata == nullptr ? " NULL" : " Non-NULL")
                << " extra data cannot have size of "
                << codec_context->extradata_size << ".";
     return false;
   }
 
   std::vector<uint8_t> extra_data;
   if (codec_context->extradata_size > 0) {
     extra_data.assign(codec_context->extradata,
                       codec_context->extradata + codec_context->extradata_size);
   }
   config->Initialize(codec,
                      sample_format,
                      channel_layout,
                      sample_rate,
                      extra_data,
                      is_encrypted,
                      seek_preroll,
                      codec_context->delay);
-
-  if (codec != kCodecOpus) {
+  if (codec != kCodecOpus && codec != kCodecAC3 && codec != kCodecEAC3) {

[ddorwin, 2016/01/07 19:12:43]

Suggest:
// Verify XXX for codecs for which FFmpeg provides a sample_fmt.

[servolk, 2016/01/07 21:17:36]

Done.

     DCHECK_EQ(av_get_bytes_per_sample(codec_context->sample_fmt) * 8,
               config->bits_per_channel());
   }
 
   return true;
 }
 
 bool AVStreamToAudioDecoderConfig(const AVStream* stream,
                                   AudioDecoderConfig* config) {
   bool is_encrypted = false;
@@ skipping 323 matching lines @@
 }
 
 int32_t HashCodecName(const char* codec_name) {
   // Use the first 32-bits from the SHA1 hash as the identifier.
   int32_t hash;
   memcpy(&hash, base::SHA1HashString(codec_name).substr(0, 4).c_str(), 4);
   return hash;
 }
 
 }  // namespace media