Add h264 prefix NAL parser impl for enabling frame-marking

common_video/BUILD.gn

@@ -21,6 +21,8 @@ rtc_static_library("common_video") {
     "h264/h264_common.h",
     "h264/pps_parser.cc",
     "h264/pps_parser.h",
+    "h264/prefix_parser.cc",
+    "h264/prefix_parser.h",
     "h264/profile_level_id.h",
     "h264/sps_parser.cc",
     "h264/sps_parser.h",

common_video/h264/h264_common.h

@@ -42,6 +42,7 @@ enum NaluType : uint8_t {
   kEndOfSequence = 10,
   kEndOfStream = 11,
   kFiller = 12,
+  kPrefix = 14,
   kStapA = 24,
   kFuA = 28
 };

common_video/h264/prefix_parser.cc

@@ -0,0 +1,85 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "common_video/h264/prefix_parser.h"
+
+#include <cstdint>
+#include <vector>
+
+#include "common_video/h264/h264_common.h"
+#include "rtc_base/bit_buffer.h"
+
+namespace {
+typedef absl::optional<webrtc::PrefixParser::PrefixState> OptionalPrefix;
+
+#define RETURN_EMPTY_ON_FAIL(x) \
+  if (!(x)) {                   \
+    return OptionalPrefix();       \
+  }
+}  // namespace
+
+namespace webrtc {
+
+PrefixParser::PrefixState::PrefixState() = default;
+PrefixParser::PrefixState::PrefixState(const PrefixState&) = default;
+PrefixParser::PrefixState::~PrefixState() = default;
+
+// General note: this is based off the 02/2016 version of the H.264 standard.
+// You can find it on this page:
+// http://www.itu.int/rec/T-REC-H.264
+
+// Unpack RBSP and parse SVC extension state from the supplied buffer.
+absl::optional<PrefixParser::PrefixState> PrefixParser::ParsePrefix(
+    const uint8_t* data,
+                                                        size_t length) {
+  std::vector<uint8_t> unpacked_buffer = H264::ParseRbsp(data, length);
+  rtc::BitBuffer bit_buffer(unpacked_buffer.data(), unpacked_buffer.size());
+  return ParsePrefixUpToSvcExtension(&bit_buffer);
+}
+
+absl::optional<PrefixParser::PrefixState> PrefixParser::ParsePrefixUpToSvcExtension(
+    rtc::BitBuffer* buffer) {
+  // Now, we need to use a bit buffer to parse through the actual SVC extension
+  // format. See Section 7.3.1 ("NAL unit syntax") and 7.3.1.1 ("NAL unit header
+  // SVC extension syntax") of the H.264 standard for a complete description.
+
+  PrefixState svc_extension;
+
+  uint32_t svc_extension_flag = 0;
+  // Make sure the svc_extension_flag is on.
+  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension_flag, 1));
+  if (!svc_extension_flag)
+    return OptionalPrefix();
+
+  // idr_flag: u(1)
+  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.idr_flag, 1));
+  // priority_id: u(6)
+  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.priority_id, 6));
+  // no_inter_layer_pred_flag: u(1)
+  RETURN_EMPTY_ON_FAIL(
+      buffer->ReadBits(&svc_extension.no_inter_layer_pred_flag, 1));
+  // dependency_id: u(3)
+  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.dependency_id, 3));
+  // quality_id: u(4)
+  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.quality_id, 4));
+  // temporal_id: u(3)
+  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.temporal_id, 3));
+  // use_ref_base_pic_flag: u(1)
+  RETURN_EMPTY_ON_FAIL(
+      buffer->ReadBits(&svc_extension.use_ref_base_pic_flag, 1));
+  // discardable_flag: u(1)
+  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.discardable_flag, 1));
+  // output_flag: u(1)
+  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.output_flag, 1));
+
+  return OptionalPrefix(svc_extension);
+}
+
+}  // namespace webrtc

common_video/h264/prefix_parser.h

@@ -0,0 +1,53 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef COMMON_VIDEO_H264_PREFIX_PARSER_H_
+#define COMMON_VIDEO_H264_PREFIX_PARSER_H_
+
+#include "absl/types/optional.h"
+
+namespace rtc {
+class BitBuffer;
+}
+
+namespace webrtc {
+
+// A class for parsing out SVC extension data from an H264 prefix NALU
+class PrefixParser {
+ public:
+  // The parsed state of the SVC extension. Only some select values are stored.
+  // Add more as they are actually needed.
+  struct PrefixState {
+    PrefixState();
+    PrefixState(const PrefixState&);
+    ~PrefixState();
+
+    uint32_t idr_flag = 0;
+    uint32_t priority_id = 0;
+    uint32_t no_inter_layer_pred_flag = 1;
+    uint32_t dependency_id = 0;
+    uint32_t quality_id = 0;
+    uint32_t temporal_id = 0;
+    uint32_t use_ref_base_pic_flag = 0;
+    uint32_t discardable_flag = 1;
+    uint32_t output_flag = 1;
+  };
+
+  // Unpack RBSP and parse prefix state from the supplied buffer.
+  static absl::optional<PrefixState> ParsePrefix(const uint8_t* data, size_t length);
+
+ protected:
+  // Parse the prefix NAL, up till the SVC extension part, for a bit buffer where RBSP
+  // decoding has already been performed.
+  static absl::optional<PrefixState> ParsePrefixUpToSvcExtension(rtc::BitBuffer* buffer);
+};
+
+}  // namespace webrtc
+#endif  // COMMON_VIDEO_H264_PREFIX_PARSER_H_