Add H264 bitstream rewriting to limit frame reordering marker in header

webrtc/common_video/h264/sps_vui_rewriter.h

+/*
+ *  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 WEBRTC_COMMON_VIDEO_H264_SPS_VUI_REWRITER_H_
+#define WEBRTC_COMMON_VIDEO_H264_SPS_VUI_REWRITER_H_
+
+#include "webrtc/base/buffer.h"
+#include "webrtc/base/optional.h"
+#include "webrtc/common_video/h264/sps_parser.h"
+
+namespace rtc {
+class BitBuffer;
+}
+
+namespace webrtc {
+
+// A class that can parse an SPS block of a NAL unit and if necessary
+// creates a copy with updated settings to allow for faster decoding for streams
+// that use picture order count type 0. Streams in that format incur additional
+// delay because it allows decode order to differ from render order.
+// The mechanism used is to rewrite (edit or add) the SPS's VUI to contain
+// restrictions on the maximum number of reordered pictures. This reduces
+// latency significantly, though it still adds about a frame of latency to
+// decoding.
+class SpsVuiRewriter : private SpsParser {
+ public:
+  enum class ParseResult { kFailure, kPocOk, kVuiOk, kVuiRewritten };
+
+  // Parses an SPS block and if necessary copies it and rewrites the VUI.
+  // Returns kFailure on failure, kParseOk if parsing succeeded and no update
+  // was necessary and kParsedAndModified if an updated copy of buffer was
+  // written to destination. destination may be populated with some data even if
+  // no rewrite was necessary, but the end offset should remain unchanged.
+  // Unless parsing fails, the sps parameter will be populated with the parsed
+  // SPS state. This function assumes that any previous headers
+  // (NALU start, type, Stap-A, etc) have already been parsed and that RBSP
+  // decoding has been performed.
+  static ParseResult ParseAndRewriteSps(const uint8_t* buffer,
+                                        size_t length,
+                                        rtc::Optional<SpsParser::SpsState>* sps,
+                                        rtc::Buffer* destination);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_COMMON_VIDEO_H264_SPS_VUI_REWRITER_H_