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// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CAST_STREAMING_RTP_PACKET_PARSER_H_
#define CAST_STREAMING_RTP_PACKET_PARSER_H_
#include <chrono>
#include "absl/types/optional.h"
#include "absl/types/span.h"
#include "cast/streaming/frame_id.h"
#include "cast/streaming/rtp_defines.h"
#include "cast/streaming/rtp_time.h"
#include "cast/streaming/ssrc.h"
namespace openscreen {
namespace cast {
// Parses RTP packets for all frames in the same Cast RTP stream. One
// RtpPacketParser instance should be used for all RTP packets having the same
// SSRC.
//
// Note that the parser is not stateless: One of its responsibilities is to
// bit-expand values that exist in a truncated form within the packets. It
// tracks the progression of those values in a live system to re-constitute such
// values.
class RtpPacketParser {
public:
struct ParseResult {
// Elements from RTP packet header.
// https://tools.ietf.org/html/rfc3550#section-5
RtpPayloadType payload_type;
uint16_t sequence_number; // Wrap-around packet transmission counter.
RtpTimeTicks rtp_timestamp; // The media timestamp.
// Elements from Cast header (at beginning of RTP payload).
bool is_key_frame;
FrameId frame_id;
FramePacketId packet_id; // Always in the range [0,max_packet_id].
FramePacketId max_packet_id;
FrameId referenced_frame_id; // ID of frame required to decode this one.
std::chrono::milliseconds new_playout_delay{}; // Ignore if non-positive.
// Portion of the |packet| that was passed into Parse() that contains the
// payload. WARNING: This memory region is only valid while the original
// |packet| memory remains valid.
absl::Span<const uint8_t> payload;
ParseResult();
~ParseResult();
};
explicit RtpPacketParser(Ssrc sender_ssrc);
~RtpPacketParser();
// Parses the packet. The caller should use InspectPacketForRouting()
// beforehand to ensure that the packet is meant to be parsed by this
// instance. Returns absl::nullopt if the |packet| was corrupt.
absl::optional<ParseResult> Parse(absl::Span<const uint8_t> packet);
private:
const Ssrc sender_ssrc_;
// Tracks recently-parsed RTP timestamps so that the truncated values can be
// re-expanded into full-form.
RtpTimeTicks last_parsed_rtp_timestamp_;
// The highest frame ID seen in any RTP packets so far. This is tracked so
// that the truncated frame ID fields in RTP packets can be re-expanded into
// full-form.
FrameId highest_rtp_frame_id_;
};
} // namespace cast
} // namespace openscreen
#endif // CAST_STREAMING_RTP_PACKET_PARSER_H_
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