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| 1 | +/* |
| 2 | + * Copyright (c) 2016 The WebRTC project authors. All Rights Reserved. |
| 3 | + * |
| 4 | + * Use of this source code is governed by a BSD-style license |
| 5 | + * that can be found in the LICENSE file in the root of the source |
| 6 | + * tree. An additional intellectual property rights grant can be found |
| 7 | + * in the file PATENTS. All contributing project authors may |
| 8 | + * be found in the AUTHORS file in the root of the source tree. |
| 9 | + */ |
| 10 | + |
| 11 | +#include "common_video/h264/prefix_parser.h" |
| 12 | + |
| 13 | +#include <cstdint> |
| 14 | +#include <vector> |
| 15 | + |
| 16 | +#include "common_video/h264/h264_common.h" |
| 17 | +#include "rtc_base/bit_buffer.h" |
| 18 | + |
| 19 | +namespace { |
| 20 | +typedef absl::optional<webrtc::PrefixParser::PrefixState> OptionalPrefix; |
| 21 | + |
| 22 | +#define RETURN_EMPTY_ON_FAIL(x) \ |
| 23 | + if (!(x)) { \ |
| 24 | + return OptionalPrefix(); \ |
| 25 | + } |
| 26 | +} // namespace |
| 27 | + |
| 28 | +namespace webrtc { |
| 29 | + |
| 30 | +PrefixParser::PrefixState::PrefixState() = default; |
| 31 | +PrefixParser::PrefixState::PrefixState(const PrefixState&) = default; |
| 32 | +PrefixParser::PrefixState::~PrefixState() = default; |
| 33 | + |
| 34 | +// General note: this is based off the 02/2016 version of the H.264 standard. |
| 35 | +// You can find it on this page: |
| 36 | +// http://www.itu.int/rec/T-REC-H.264 |
| 37 | + |
| 38 | +// Unpack RBSP and parse SVC extension state from the supplied buffer. |
| 39 | +absl::optional<PrefixParser::PrefixState> PrefixParser::ParsePrefix( |
| 40 | + const uint8_t* data, |
| 41 | + size_t length) { |
| 42 | + std::vector<uint8_t> unpacked_buffer = H264::ParseRbsp(data, length); |
| 43 | + rtc::BitBuffer bit_buffer(unpacked_buffer.data(), unpacked_buffer.size()); |
| 44 | + return ParsePrefixUpToSvcExtension(&bit_buffer); |
| 45 | +} |
| 46 | + |
| 47 | +absl::optional<PrefixParser::PrefixState> PrefixParser::ParsePrefixUpToSvcExtension( |
| 48 | + rtc::BitBuffer* buffer) { |
| 49 | + // Now, we need to use a bit buffer to parse through the actual SVC extension |
| 50 | + // format. See Section 7.3.1 ("NAL unit syntax") and 7.3.1.1 ("NAL unit header |
| 51 | + // SVC extension syntax") of the H.264 standard for a complete description. |
| 52 | + |
| 53 | + PrefixState svc_extension; |
| 54 | + |
| 55 | + uint32_t svc_extension_flag = 0; |
| 56 | + // Make sure the svc_extension_flag is on. |
| 57 | + RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension_flag, 1)); |
| 58 | + if (!svc_extension_flag) |
| 59 | + return OptionalPrefix(); |
| 60 | + |
| 61 | + // idr_flag: u(1) |
| 62 | + RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.idr_flag, 1)); |
| 63 | + // priority_id: u(6) |
| 64 | + RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.priority_id, 6)); |
| 65 | + // no_inter_layer_pred_flag: u(1) |
| 66 | + RETURN_EMPTY_ON_FAIL( |
| 67 | + buffer->ReadBits(&svc_extension.no_inter_layer_pred_flag, 1)); |
| 68 | + // dependency_id: u(3) |
| 69 | + RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.dependency_id, 3)); |
| 70 | + // quality_id: u(4) |
| 71 | + RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.quality_id, 4)); |
| 72 | + // temporal_id: u(3) |
| 73 | + RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.temporal_id, 3)); |
| 74 | + // use_ref_base_pic_flag: u(1) |
| 75 | + RETURN_EMPTY_ON_FAIL( |
| 76 | + buffer->ReadBits(&svc_extension.use_ref_base_pic_flag, 1)); |
| 77 | + // discardable_flag: u(1) |
| 78 | + RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.discardable_flag, 1)); |
| 79 | + // output_flag: u(1) |
| 80 | + RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.output_flag, 1)); |
| 81 | + |
| 82 | + return OptionalPrefix(svc_extension); |
| 83 | +} |
| 84 | + |
| 85 | +} // namespace webrtc |
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