Add H264 bitstream rewriting to limit frame reordering marker in header

webrtc/modules/rtp_rtcp/source/h264/sps_parser.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_MODULES_RTP_RTCP_SOURCE_H264_SPS_PARSER_H_
+#define WEBRTC_MODULES_RTP_RTCP_SOURCE_H264_SPS_PARSER_H_
+
+#include "webrtc/base/common.h"
+#include "webrtc/base/optional.h"
+
+namespace rtc {
+class BitBuffer;
+}
+
+namespace webrtc {
+
+// A class for parsing out sequence parameter set (SPS) data from an H264 NALU.
+class SpsParser {
+ public:
+  SpsParser();

[noahric, 2016/05/18 01:35:07]

Yeah, this is really weird now; you use this constructor + ParseFrom, or the
other constructor + Parse(). This should really just have two (static)
Parse[...] methods that return SpsState as an out param.

So:
class SpsParser {
 public:
  // Parses the given buffer for SpsState. On success, returns true and writes
SPS
  // information to |out_sps_state|, which must be non-null.
  static bool Parse(const uint8_t* buffer, size_t buffer_length, SpsState*
out_sps_state);

[sprang_webrtc, 2016/05/20 16:11:00]

Acknowledged.

+  SpsParser(const uint8_t* buffer, size_t buffer_length);
+
+  // Parses the SPS to completion. Returns true if the SPS was parsed correctly.
+  bool Parse();
+
+  // Alternative parsing method, using a supplied BitBuffer where the RBSP
+  // decoding has already been performed. Useful if further parsing of the NAL
+  // shall follow.
+  bool ParseFromRbspDecodedBitBuffer(rtc::BitBuffer* buffer);

[noahric, 2016/05/18 01:35:07]

I still think you want to get rid of this. It's strange how it modifies buffer
(e.g. it makes more sense, in abstract, to have the caller do buffer.Data(),
buffer.Length() on the other parse function), and requires the parser at a
certain point.

[sprang_webrtc, 2016/05/20 16:11:00]

Acknowledged.

+
+  // The parsed state of the SPS. Only some select values are stored.
+  // Add more as they are actually needed.
+  struct SpsState {
+    SpsState() = default;
+
+    uint32_t width = 0;
+    uint32_t height = 0;
+    uint32_t delta_pic_order_always_zero_flag = 0;
+    uint32_t separate_colour_plane_flag = 0;
+    uint32_t frame_mbs_only_flag = 0;
+    uint32_t log2_max_frame_num_minus4 = 0;
+    uint32_t log2_max_pic_order_cnt_lsb_minus4 = 0;
+    uint32_t pic_order_cnt_type = 0;
+    uint32_t max_num_ref_frames = 0;
+    uint32_t vui_params_present = 0;
+  };
+
+  // Get the parsed SPS state.
+  const rtc::Optional<SpsState>& GetState() const;
+
+ private:
+  const uint8_t* const buffer_;
+  const size_t buffer_length_;
+  rtc::Optional<SpsState> state_;
+};
+
+}  // namespace webrtc
+#endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_H264_SPS_PARSER_H_