Add H264 bitstream rewriting to limit frame reordering marker in header

webrtc/modules/rtp_rtcp/source/h264/h264_common.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_H264_COMMON_H_
+#define WEBRTC_MODULES_RTP_RTCP_SOURCE_H264_H264_COMMON_H_
+
+#include <memory>
+#include <vector>
+
+#include "webrtc/base/common.h"
+#include "webrtc/base/bytebuffer.h"
+
+namespace webrtc {
+
+class H264Common {
+ public:
+  // The size of a NALU header {0 0 0 1}.

[noahric, 2016/05/18 01:35:06]

Three byte start codes are also valid, but assuming something else (jitter
buffer?) is ensuring a 4 byte header, I'd add that to the comment.

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

I think this has worked because the standard mandates 4 byte start sequences for
SPS, PPS and the first NAL of an access unit. And that's what we care about.
Have updated this and parsing to handle both though.

+  static const size_t kNaluHeaderSize;
+
+  // The size of a NALU header plus the type byte.
+  static const size_t kNaluHeaderAndTypeSize;
+
+  enum NaluType : uint8_t { kSps = 0x7, kPps = 0x8, kIdr = 0x5 };

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

While you are here, add Sei, in case someone needs it. They get inserted by some
implementations (e.g. the h264 encoder on iOS).

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

Done.

+  enum SliceType : uint8_t { P = 0, B = 1, I = 2, Sp = 3, Si = 4 };
+
+  // Returns a vector of the NALU start sequences (0 0 0 1) in the given buffer.

[noahric, 2016/05/18 01:35:06]

My bad (it was my comment originally), but I'd rephrase slightly:
// Returns a vector of NALU start sequence (0 0 0 1) locations in the given
buffer.

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

Changed this to contain both offset of nal header and payload, plus size, which
simplifies a bunch of code at the expense of a few bytes of extra memory usage.

+  static std::vector<size_t> FindNaluStartOffsets(const uint8_t* buffer,
+                                                  size_t buffer_size);
+  static NaluType ParseNaluType(uint8_t data);

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

Comments for these would help.

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

Done.

+  static std::unique_ptr<rtc::ByteBufferWriter> ParseRbsp(const uint8_t* data,
+                                                          size_t length);
+  static void WriteRbsp(const uint8_t* bytes,
+                        size_t length,
+                        rtc::ByteBufferWriter* destination);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_H264_H264_COMMON_H_