53 lines
1.5 KiB
C++
53 lines
1.5 KiB
C++
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// Copyright 2018 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/codecs/ac3_audio_util.h"
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#include "packager/base/strings/string_number_conversions.h"
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#include "packager/media/base/bit_reader.h"
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#include "packager/media/base/rcheck.h"
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namespace shaka {
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namespace media {
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namespace {
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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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bool ExtractAc3Data(const std::vector<uint8_t>& ac3_data,
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uint8_t* audio_coding_mode,
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bool* lfe_channel_on) {
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BitReader bit_reader(ac3_data.data(), ac3_data.size());
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// fscod: 2 bits
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// bsid: 5 bits
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// bsmod: 3 bits
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// acmod: 3 bits
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// lfeon: 1 bit
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// bit_rate_code: 5 bits
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RCHECK(bit_reader.SkipBits(10));
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RCHECK(bit_reader.ReadBits(3, audio_coding_mode));
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RCHECK(bit_reader.ReadBits(1, lfe_channel_on));
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return true;
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}
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} // namespace
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size_t GetAc3NumChannels(const std::vector<uint8_t>& ac3_data) {
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uint8_t audio_coding_mode;
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bool lfe_channel_on;
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if (!ExtractAc3Data(ac3_data, &audio_coding_mode, &lfe_channel_on)) {
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LOG(WARNING) << "Seeing invalid AC3 data: "
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<< base::HexEncode(ac3_data.data(), ac3_data.size());
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return 0;
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}
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return kAc3NumChannelsTable[audio_coding_mode] + (lfe_channel_on ? 1 : 0);
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}
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} // namespace media
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} // namespace shaka
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