Re-add AC3/EAC3 audio demuxing support

media/formats/mp4/es_descriptor.h

 // 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.
 
 #ifndef MEDIA_FORMATS_MP4_ES_DESCRIPTOR_H_
 #define MEDIA_FORMATS_MP4_ES_DESCRIPTOR_H_
 
 #include <stdint.h>
 
 #include <vector>
 
 #include "media/base/media_export.h"
 
 namespace media {
 
 class BitReader;
 
 namespace mp4 {
 
 // The following values are extracted from ISO 14496 Part 1 Table 5 -
 // objectTypeIndication Values. Only values currently in use are included.
 enum ObjectType {
   kForbidden = 0,
-  kISO_14496_3 = 0x40,  // MPEG4 AAC
-  kISO_13818_7_AAC_LC = 0x67  // MPEG2 AAC-LC
+  kISO_14496_3 = 0x40,         // MPEG4 AAC

[ddorwin, 2016/01/04 23:22:17]

Are these complex names the best option? I wonder why this one doesn't contain
"AAC" like the next one.

[servolk, 2016/01/07 02:30:04]

I don't know. Git blame tells me these were added by acolwell@ and ycheo@ a
while ago. My only change in these lines is in adjusting the indentation of the
comments (and that was done automatically by  'git cl format'). I can change
these, if you insist, but in a separate CL, to keep this CL purely about
AC3/EAC3.

+  kISO_13818_7_AAC_LC = 0x67,  // MPEG2 AAC-LC
+  kAC3 = 0xa5,                 // AC3

[ddorwin, 2016/01/04 23:22:17]

Why do the names above have complex names while these have simple names? Is
there no ISO for them?

[servolk, 2016/01/07 02:30:04]

I believe the standard that describes AC3/EAC3 audio is ETSI TS 102 366, so we
could name those kETSI_TS_102_366_AC3 and kETSI_TS_102_366_EAC3, if you prefer.
Those shorted names were chosen by damienv@, I'm just upstreaming this from
Chromecast tree.

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

I think we should be consistent, though I'm not wild about the existing names.
dalecurtis@, WDYT?

+  kEAC3 = 0xa6                 // EAC3 / Dolby Digital Plus
 };
 
 // This class parse object type and decoder specific information from an
 // elementary stream descriptor, which is usually contained in an esds box.
 // Please refer to ISO 14496 Part 1 7.2.6.5 for more details.
 class MEDIA_EXPORT ESDescriptor {
  public:
   // Utility function to check if the given object type is AAC.
   static bool IsAAC(uint8_t object_type);
 
@@ skipping 17 matching lines @@
 
   uint8_t object_type_;
   std::vector<uint8_t> decoder_specific_info_;
 };
 
 }  // namespace mp4
 
 }  // namespace media
 
 #endif  // MEDIA_FORMATS_MP4_ES_DESCRIPTOR_H_