| // Copyright 2016 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/formats/ac3/ac3_util.h" |
| |
| #include "base/logging.h" |
| #include "base/stl_util.h" |
| #include "media/base/bit_reader.h" |
| |
| namespace media { |
| |
| namespace { |
| |
| // The size in byte of a (E-)AC3 synchronization frame header. |
| const int kHeaderSizeInByte = 8; |
| // The number of new samples per (E-)AC3 audio block. |
| const int kAudioSamplesPerAudioBlock = 256; |
| // Each synchronization frame has 6 blocks that provide 256 new audio samples. |
| const int kAudioSamplePerAc3SyncFrame = 6 * kAudioSamplesPerAudioBlock; |
| // Number of audio blocks per E-AC3 synchronization frame, indexed by |
| // numblkscod. |
| const int kBlocksPerSyncFrame[] = {1, 2, 3, 6}; |
| // Sample rates, indexed by fscod. |
| const int kSampleRate[] = {48000, 44100, 32000}; |
| // Nominal bitrates in kbps, indexed by frmsizecod / 2. |
| const int kBitrate[] = {32, 40, 48, 56, 64, 80, 96, 112, 128, 160, |
| 192, 224, 256, 320, 384, 448, 512, 576, 640}; |
| // 16-bit words per synchronization frame, indexed by frmsizecod. |
| const int kSyncFrameSizeInWordsFor44kHz[] = { |
| 69, 70, 87, 88, 104, 105, 121, 122, 139, 140, 174, 175, 208, |
| 209, 243, 244, 278, 279, 348, 349, 417, 418, 487, 488, 557, 558, |
| 696, 697, 835, 836, 975, 976, 1114, 1115, 1253, 1254, 1393, 1394}; |
| |
| // Utility for unpacking (E-)AC3 header. Note that all fields are encoded. |
| class Ac3Header { |
| public: |
| Ac3Header(const uint8_t* data, int size); |
| |
| uint32_t eac3_frame_size_code() const { return eac3_frame_size_code_; } |
| |
| uint32_t sample_rate_code() const { return sample_rate_code_; } |
| |
| uint32_t eac3_number_of_audio_block_code() const { |
| DCHECK(sample_rate_code_ != 3); |
| return eac3_number_of_audio_block_code_; |
| } |
| |
| uint32_t ac3_frame_size_code() const { return ac3_frame_size_code_; } |
| |
| private: |
| // bit[5:15] for E-AC3 |
| uint32_t eac3_frame_size_code_; |
| // bit[16:17] for (E-)AC3 |
| uint32_t sample_rate_code_; |
| // bit[18:23] for AC3 |
| uint32_t ac3_frame_size_code_; |
| // bit[18:19] for E-AC3 |
| uint32_t eac3_number_of_audio_block_code_; |
| }; |
| |
| Ac3Header::Ac3Header(const uint8_t* data, int size) { |
| DCHECK_GE(size, kHeaderSizeInByte); |
| |
| BitReader reader(data, size); |
| uint16_t sync_word; |
| reader.ReadBits(16, &sync_word); |
| DCHECK(sync_word == 0x0B77); |
| |
| reader.SkipBits(5); |
| reader.ReadBits(11, &eac3_frame_size_code_); |
| reader.ReadBits(2, &sample_rate_code_); |
| reader.ReadBits(6, &ac3_frame_size_code_); |
| eac3_number_of_audio_block_code_ = ac3_frame_size_code_ >> 4; |
| } |
| |
| // Search for next synchronization word, wihch is 0x0B-0x77. |
| const uint8_t* FindNextSyncWord(const uint8_t* const begin, |
| const uint8_t* const end) { |
| DCHECK(begin); |
| DCHECK(end); |
| DCHECK_LE(begin, end); |
| |
| const uint8_t* current = begin; |
| |
| while (current < end - 1) { |
| if (current[0] == 0x0B && current[1] == 0x77) { |
| if (current != begin) |
| DVLOG(2) << __func__ << " skip " << current - begin << " bytes."; |
| |
| return current; |
| } else if (current[1] != 0x0B) { |
| current += 2; |
| } else { |
| ++current; |
| } |
| } |
| |
| return nullptr; |
| } |
| |
| // Returns the number of audio samples represented by the given E-AC3 |
| // synchronization frame. |
| int ParseEac3SyncFrameSampleCount(Ac3Header& header) { |
| unsigned blocks = |
| header.sample_rate_code() == 0x03 |
| ? 6 |
| : kBlocksPerSyncFrame[header.eac3_number_of_audio_block_code()]; |
| return kAudioSamplesPerAudioBlock * blocks; |
| } |
| |
| // Returns the size in bytes of the given E-AC3 synchronization frame. |
| int ParseEac3SyncFrameSize(Ac3Header& header) { |
| return 2 * (header.eac3_frame_size_code() + 1); |
| } |
| |
| // Returns the number of audio samples in an AC3 synchronization frame. |
| int GetAc3SyncFrameSampleCount() { |
| return kAudioSamplePerAc3SyncFrame; |
| } |
| |
| // Returns the size in bytes of the given AC3 synchronization frame. |
| int ParseAc3SyncFrameSize(Ac3Header& header) { |
| if (header.sample_rate_code() >= base::size(kSampleRate) || |
| header.ac3_frame_size_code() >= |
| base::size(kSyncFrameSizeInWordsFor44kHz)) { |
| DVLOG(2) << __func__ << " Invalid frame header." |
| << " fscod:" << header.sample_rate_code() |
| << " frmsizecod:" << header.ac3_frame_size_code(); |
| return -1; |
| } |
| |
| // See http://atsc.org/wp-content/uploads/2015/03/A52-201212-17.pdf table |
| // 5.18, frame size code table. |
| |
| int sample_rate = kSampleRate[header.sample_rate_code()]; |
| if (sample_rate == 44100) { |
| return 2 * kSyncFrameSizeInWordsFor44kHz[header.ac3_frame_size_code()]; |
| } |
| |
| int bitrate = kBitrate[header.ac3_frame_size_code() / 2]; |
| if (sample_rate == 32000) { |
| return 6 * bitrate; |
| } |
| |
| // sample_rate == 48000 |
| return 4 * bitrate; |
| } |
| |
| // Returns the total number of audio samples in the given buffer, which contains |
| // several complete (E-)AC3 syncframes. |
| int ParseTotalSampleCount(const uint8_t* data, size_t size, bool is_eac3) { |
| DCHECK(data); |
| |
| if (size < kHeaderSizeInByte) { |
| return 0; |
| } |
| |
| const uint8_t* const end = data + size; |
| const uint8_t* current = FindNextSyncWord(data, end); |
| int total_sample_count = 0; |
| |
| while (current && end - current > kHeaderSizeInByte) { |
| Ac3Header header(current, end - current); |
| |
| int frame_size = is_eac3 ? ParseEac3SyncFrameSize(header) |
| : ParseAc3SyncFrameSize(header); |
| int sample_count = is_eac3 ? ParseEac3SyncFrameSampleCount(header) |
| : GetAc3SyncFrameSampleCount(); |
| |
| if (frame_size > 0 && sample_count > 0) { |
| current += frame_size; |
| if (current > end) { |
| DVLOG(2) << __func__ << " Incomplete frame, missing " << current - end |
| << " bytes."; |
| break; |
| } |
| |
| total_sample_count += sample_count; |
| } else { |
| DVLOG(2) |
| << __func__ |
| << " Invalid frame, skip 2 bytes to find next synchronization word."; |
| current += 2; |
| } |
| |
| current = FindNextSyncWord(current, end); |
| } |
| |
| return total_sample_count; |
| } |
| |
| } // namespace anonymous |
| |
| // static |
| int Ac3Util::ParseTotalAc3SampleCount(const uint8_t* data, size_t size) { |
| return ParseTotalSampleCount(data, size, false); |
| } |
| |
| // static |
| int Ac3Util::ParseTotalEac3SampleCount(const uint8_t* data, size_t size) { |
| return ParseTotalSampleCount(data, size, true); |
| } |
| |
| } // namespace media |