144 lines
4.6 KiB
C++
144 lines
4.6 KiB
C++
// Copyright 2017 Google Inc. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file or at
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// https://developers.google.com/open-source/licenses/bsd
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#include "packager/media/formats/mp2t/ac3_header.h"
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#include "packager/media/base/bit_reader.h"
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#include "packager/media/base/bit_writer.h"
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#include "packager/media/formats/mp2t/mp2t_common.h"
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namespace shaka {
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namespace media {
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namespace mp2t {
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namespace {
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// ASTC Standard A/52:2012 Table 5.6 Sample Rate Codes.
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const uint32_t kAc3SampleRateTable[] = {48000, 44100, 32000};
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// ASTC Standard A/52:2012 Table 5.8 Audio Coding Mode.
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const uint8_t kAc3NumChannelsTable[] = {2, 1, 2, 3, 3, 4, 4, 5};
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// ATSC Standard A/52:2012 Table 5.18 Frame Size Code Table
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// (in words = 16 bits).
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const size_t kFrameSizeCodeTable[][3] = {
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{96, 69, 64}, {96, 70, 64}, {120, 87, 80},
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{120, 88, 80}, {144, 104, 96}, {144, 105, 96},
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{168, 121, 112}, {168, 122, 112}, {192, 139, 128},
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{192, 140, 128}, {240, 174, 160}, {240, 175, 160},
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{288, 208, 192}, {288, 209, 192}, {336, 243, 224},
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{336, 244, 224}, {384, 278, 256}, {384, 279, 256},
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{480, 348, 320}, {480, 349, 320}, {576, 417, 384},
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{576, 418, 384}, {672, 487, 448}, {672, 488, 448},
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{768, 557, 512}, {768, 558, 512}, {960, 696, 640},
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{960, 697, 640}, {1152, 835, 768}, {1152, 836, 768},
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{1344, 975, 896}, {1344, 976, 896}, {1536, 1114, 1024},
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{1536, 1115, 1024}, {1728, 1253, 1152}, {1728, 1254, 1152},
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{1920, 1393, 1280}, {1920, 1394, 1280},
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};
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} // namespace
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bool Ac3Header::IsSyncWord(const uint8_t* buf) const {
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DCHECK(buf);
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// ATSC Standard A/52:2012 5.4.1 syncinfo: Synchronization Information.
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return buf[0] == 0x0B && buf[1] == 0x77;
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}
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size_t Ac3Header::GetMinFrameSize() const {
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// Arbitrary. Actual frame size starts with 96 words.
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const size_t kMinAc3FrameSize = 10u;
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return kMinAc3FrameSize;
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}
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size_t Ac3Header::GetSamplesPerFrame() const {
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// ATSC Standard A/52:2012
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// Annex A: AC-3 Elementary Streams in the MPEG-2 Multiplex.
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const size_t kSamplesPerAc3Frame = 1536;
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return kSamplesPerAc3Frame;
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}
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bool Ac3Header::Parse(const uint8_t* audio_frame, size_t audio_frame_size) {
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BitReader frame(audio_frame, audio_frame_size);
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// ASTC Standard A/52:2012 5. BIT STREAM SYNTAX.
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// syncinfo: synchronization information section.
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uint16_t syncword;
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RCHECK(frame.ReadBits(16, &syncword));
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RCHECK(syncword == 0x0B77);
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uint16_t crc1;
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RCHECK(frame.ReadBits(16, &crc1));
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RCHECK(frame.ReadBits(2, &fscod_));
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RCHECK(fscod_ < arraysize(kAc3SampleRateTable));
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RCHECK(frame.ReadBits(6, &frmsizecod_));
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RCHECK(frmsizecod_ < arraysize(kFrameSizeCodeTable));
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// bsi: bit stream information section.
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RCHECK(frame.ReadBits(5, &bsid_));
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RCHECK(frame.ReadBits(3, &bsmod_));
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RCHECK(frame.ReadBits(3, &acmod_));
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RCHECK(acmod_ < arraysize(kAc3NumChannelsTable));
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// If 3 front channels.
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if ((acmod_ & 0x01) && (acmod_ != 0x01))
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RCHECK(frame.SkipBits(2)); // cmixlev.
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// If a surround channel exists.
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if (acmod_ & 0x04)
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RCHECK(frame.SkipBits(2)); // surmixlev.
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// If in 2/0 mode.
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if (acmod_ == 0x02)
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RCHECK(frame.SkipBits(2)); // dsurmod.
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RCHECK(frame.ReadBits(1, &lfeon_));
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return true;
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}
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size_t Ac3Header::GetHeaderSize() const {
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// Unlike ADTS, for AC3, the whole frame is included in the media sample, so
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// return 0 header size.
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return 0;
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}
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size_t Ac3Header::GetFrameSize() const {
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DCHECK_LT(fscod_, arraysize(kAc3SampleRateTable));
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DCHECK_LT(frmsizecod_, arraysize(kFrameSizeCodeTable));
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return kFrameSizeCodeTable[frmsizecod_][fscod_] * 2;
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}
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void Ac3Header::GetAudioSpecificConfig(std::vector<uint8_t>* buffer) const {
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DCHECK(buffer);
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buffer->clear();
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BitWriter config(buffer);
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// Accoding to ETSI TS 102 366 V1.3.1 (2014-08) F.4 AC3SpecificBox.
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config.WriteBits(fscod_, 2);
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config.WriteBits(bsid_, 5);
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config.WriteBits(bsmod_, 3);
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config.WriteBits(acmod_, 3);
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config.WriteBits(lfeon_, 1);
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const uint8_t bit_rate_code = frmsizecod_ >> 1;
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config.WriteBits(bit_rate_code, 5);
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config.Flush();
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}
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uint8_t Ac3Header::GetObjectType() const {
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// Only useful for AAC. Return a dummy value instead.
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return 0;
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}
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uint32_t Ac3Header::GetSamplingFrequency() const {
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DCHECK_LT(fscod_, arraysize(kAc3SampleRateTable));
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return kAc3SampleRateTable[fscod_];
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}
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uint8_t Ac3Header::GetNumChannels() const {
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DCHECK_LT(acmod_, arraysize(kAc3NumChannelsTable));
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return kAc3NumChannelsTable[acmod_] + (lfeon_ ? 1 : 0);
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}
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} // namespace mp2t
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} // namespace media
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} // namespace shaka
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