86 lines
3.1 KiB
C++
86 lines
3.1 KiB
C++
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/*
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* Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "common_video/h264/prefix_parser.h"
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#include <cstdint>
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#include <vector>
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#include "common_video/h264/h264_common.h"
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#include "rtc_base/bit_buffer.h"
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namespace {
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typedef absl::optional<webrtc::PrefixParser::PrefixState> OptionalPrefix;
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#define RETURN_EMPTY_ON_FAIL(x) \
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if (!(x)) { \
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return OptionalPrefix(); \
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}
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} // namespace
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namespace webrtc {
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PrefixParser::PrefixState::PrefixState() = default;
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PrefixParser::PrefixState::PrefixState(const PrefixState&) = default;
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PrefixParser::PrefixState::~PrefixState() = default;
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// General note: this is based off the 02/2016 version of the H.264 standard.
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// You can find it on this page:
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// http://www.itu.int/rec/T-REC-H.264
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// Unpack RBSP and parse SVC extension state from the supplied buffer.
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absl::optional<PrefixParser::PrefixState> PrefixParser::ParsePrefix(
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const uint8_t* data,
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size_t length) {
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std::vector<uint8_t> unpacked_buffer = H264::ParseRbsp(data, length);
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rtc::BitBuffer bit_buffer(unpacked_buffer.data(), unpacked_buffer.size());
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return ParsePrefixUpToSvcExtension(&bit_buffer);
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}
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absl::optional<PrefixParser::PrefixState> PrefixParser::ParsePrefixUpToSvcExtension(
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rtc::BitBuffer* buffer) {
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// Now, we need to use a bit buffer to parse through the actual SVC extension
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// format. See Section 7.3.1 ("NAL unit syntax") and 7.3.1.1 ("NAL unit header
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// SVC extension syntax") of the H.264 standard for a complete description.
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PrefixState svc_extension;
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uint32_t svc_extension_flag = 0;
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// Make sure the svc_extension_flag is on.
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RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension_flag, 1));
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if (!svc_extension_flag)
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return OptionalPrefix();
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// idr_flag: u(1)
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RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.idr_flag, 1));
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// priority_id: u(6)
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RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.priority_id, 6));
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// no_inter_layer_pred_flag: u(1)
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RETURN_EMPTY_ON_FAIL(
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buffer->ReadBits(&svc_extension.no_inter_layer_pred_flag, 1));
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// dependency_id: u(3)
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RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.dependency_id, 3));
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// quality_id: u(4)
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RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.quality_id, 4));
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// temporal_id: u(3)
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RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.temporal_id, 3));
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// use_ref_base_pic_flag: u(1)
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RETURN_EMPTY_ON_FAIL(
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buffer->ReadBits(&svc_extension.use_ref_base_pic_flag, 1));
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// discardable_flag: u(1)
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RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.discardable_flag, 1));
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// output_flag: u(1)
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RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.output_flag, 1));
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return OptionalPrefix(svc_extension);
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}
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} // namespace webrtc
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