Update WebmMuxer for audio component of MediaStream recording.

media/filters/opus_header_constants.h

+// Copyright 2015 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_FILTERS_OPUS_HEADER_CONSTANTS_H_
+#define MEDIA_FILTERS_OPUS_HEADER_CONSTANTS_H_
+
+namespace media {
+
+// The Opus specification is part of IETF RFC 6716:
+// http://tools.ietf.org/html/rfc6716
+
+// Opus Extra Data contents:
+// - "OpusHead" magic signature (64 bits)
+// - version number (8 bits)
+// - Channels C (8 bits)
+// - Pre-skip (16 bits)
+// - Sampling rate (32 bits)
+// - Gain in dB (16 bits, S7.8)
+// - Mapping (8 bits, 0=single stream (mono/stereo) 1=Vorbis mapping,
+//            2..254: reserved, 255: multistream with no mapping)
+//
+// - if (mapping != 0)
+//    - N = totel number of streams (8 bits)
+//    - M = number of paired streams (8 bits)
+//    - C times channel origin
+//         - if (C<2*M)
+//            - stream = byte/2
+//            - if (byte&0x1 == 0)
+//                - left
+//              else
+//                - right
+//         - else
+//            - stream = byte-M
+
+// Default audio output channel layout. Used to initialize |stream_map| in
+// OpusExtraData, and passed to opus_multistream_decoder_create() when the
+// extra data does not contain mapping information. The values are valid only
+// for mono and stereo output: Opus streams with more than 2 channels require a
+// stream map.
+static const int kMaxChannelsWithDefaultLayout = 2;

[miu, 2015/11/03 04:18:29]

Per discussion on chromium-dev@ (about a month ago), make this an enum instead
of a static const int, to allow the compiler to not have to allocate storage for
this constant.

[ajose, 2015/11/03 23:06:22]

Done.

+static const uint8 kDefaultOpusChannelLayout[kMaxChannelsWithDefaultLayout] = {
+    0, 1};
+
+enum {
+  // Opus uses Vorbis channel mapping, and Vorbis channel mapping specifies
+  // mappings for up to 8 channels. This information is part of the Vorbis I
+  // Specification:
+  // http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html
+  OPUS_MAX_VORBIS_CHANNELS = 8,
+
+  // Size of the Opus extra data excluding optional mapping information.
+  OPUS_EXTRADATA_SIZE = 19,
+  // Offset for magic signature "OpusHead"
+  OPUS_EXTRADATA_LABEL_OFFSET = 0,
+  // Offset to the Opus version number
+  OPUS_EXTRADATA_VERSION_OFFSET = 8,
+  // Offset to the channel count byte in the Opus extra data
+  OPUS_EXTRADATA_CHANNELS_OFFSET = 9,
+  // Offset to the pre-skip value in the Opus extra data
+  OPUS_EXTRADATA_SKIP_SAMPLES_OFFSET = 10,
+  // Offset to the sampling rate value in the Opus extra data
+  OPUS_EXTRADATA_SAMPLE_RATE_OFFSET = 12,
+  // Offset to the gain value in the Opus extra data
+  OPUS_EXTRADATA_GAIN_OFFSET = 16,
+  // Offset to the channel mapping byte in the Opus extra data
+  OPUS_EXTRADATA_CHANNEL_MAPPING_OFFSET = 18,
+
+  // Extra Data contains a stream map, beyond the always present
+  // |OPUS_EXTRADATA_SIZE| bytes of data. The mapping data contains stream
+  // count, coupling information, and per channel mapping values:
+  //   - Byte 0: Number of streams.
+  //   - Byte 1: Number coupled.
+  //   - Byte 2: Starting at byte 2 are |extra_data->channels| uint8 mapping
+  //             values.
+  OPUS_EXTRADATA_NUM_STREAMS_OFFSET = OPUS_EXTRADATA_SIZE,
+  OPUS_EXTRADATA_NUM_COUPLED_OFFSET = OPUS_EXTRADATA_NUM_STREAMS_OFFSET + 1,
+  OPUS_EXTRADATA_STREAM_MAP_OFFSET = OPUS_EXTRADATA_NUM_STREAMS_OFFSET + 2,
+};
+
+// Vorbis channel ordering for streams with >= 2 channels:
+// 2 Channels
+//   L, R
+// 3 Channels
+//   L, Center, R
+// 4 Channels
+//   Front L, Front R, Back L, Back R
+// 5 Channels
+//   Front L, Center, Front R, Back L, Back R
+// 6 Channels (5.1)
+//   Front L, Center, Front R, Back L, Back R, LFE
+// 7 channels (6.1)
+//   Front L, Front Center, Front R, Side L, Side R, Back Center, LFE
+// 8 Channels (7.1)
+//   Front L, Center, Front R, Side L, Side R, Back L, Back R, LFE
+//
+// Channel ordering information is taken from section 4.3.9 of the Vorbis I
+// Specification:
+// http://xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-800004.3.9
+
+// These are the FFmpeg channel layouts expressed using the position of each
+// channel in the output stream from libopus.
+static const uint8_t kFFmpegChannelDecodingLayouts [OPUS_MAX_VORBIS_CHANNELS]

[miu, 2015/11/03 04:18:28]

The lazy class idea is not needed.  There should not be any static-initializer
code generated for these arrays.

These arrays need their declaration separated from their definition.  In the
opus_constants.h file (please delete "header" from the name):

  extern const uint8 kDefaultOpusChannelLayout[kMaxChannelsWithDefaultLayout];
  
  extern const uint8_t
kFFmpegChannelDecodingLayouts[OPUS_MAX_VORBIS_CHANNELS][OPUS_MAX_VORBIS_CHANNELS];
  
  extern const uint8_t
kOpusVorbisChannelMap[OPUS_MAX_VORBIS_CHANNELS][OPUS_MAX_VORBIS_CHANNELS];

In an opus_constants.cc file:

  namespace media {
  
  const uint8 kDefaultOpusChannelLayout[kMaxChannelsWithDefaultLayout] = { 0,
1};
  
  const uint8_t
kFFmpegChannelDecodingLayouts[OPUS_MAX_VORBIS_CHANNELS][OPUS_MAX_VORBIS_CHANNELS]
= { ...multiline initializer here... };
  
  const uint8_t
kOpusVorbisChannelMap[OPUS_MAX_VORBIS_CHANNELS][OPUS_MAX_VORBIS_CHANNELS] = {
...multiline initializer here... };
  
  }  // namespace media

[ajose, 2015/11/03 23:06:22]

Done.

+                                                   [OPUS_MAX_VORBIS_CHANNELS] =
+{
+  {0},
+
+  // Stereo: No reorder.
+  {0, 1},
+
+  // 3 Channels, from Vorbis order to:
+  //  L, R, Center
+  {0, 2, 1},
+
+  // 4 Channels: No reorder.
+  {0, 1, 2, 3},
+
+  // 5 Channels, from Vorbis order to:
+  //  Front L, Front R, Center, Back L, Back R
+  {0, 2, 1, 3, 4},
+
+  // 6 Channels (5.1), from Vorbis order to:
+  //  Front L, Front R, Center, LFE, Back L, Back R
+  {0, 2, 1, 5, 3, 4},
+
+  // 7 Channels (6.1), from Vorbis order to:
+  //  Front L, Front R, Front Center, LFE, Side L, Side R, Back Center
+  {0, 2, 1, 6, 3, 4, 5},
+
+  // 8 Channels (7.1), from Vorbis order to:
+  //  Front L, Front R, Center, LFE, Back L, Back R, Side L, Side R
+  {0, 2, 1, 7, 5, 6, 3, 4},
+};
+
+// Opus internal to Vorbis channel order mapping written in the header.
+static const uint8_t kOpusVorbisChannelMap[OPUS_MAX_VORBIS_CHANNELS]
+                                          [OPUS_MAX_VORBIS_CHANNELS] = {
+  {0},
+  {0, 1},
+  {0, 2, 1},
+  {0, 1, 2, 3},
+  {0, 4, 1, 2, 3},
+  {0, 4, 1, 2, 3, 5},
+  {0, 4, 1, 2, 3, 5, 6},
+  {0, 6, 1, 2, 3, 4, 5, 7},
+};
+
+}  // namespace media
+
+#endif  // MEDIA_FILTERS_OPUS_HEADER_CONSTANTS_H_