dtmf_buffer.cc | Explore in Territory

/*
 *  Copyright (c) 2012 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 "modules/audio_coding/neteq/dtmf_buffer.h"

#include <algorithm>  // max

#include "rtc_base/checks.h"
#include "rtc_base/logging.h"

// Modify the code to obtain backwards bit-exactness. Once bit-exactness is no
// longer required, this #define should be removed (and the code that it
// enables).
#define LEGACY_BITEXACT

namespace webrtc {

DtmfBuffer::DtmfBuffer(int fs_hz) { … }

DtmfBuffer::~DtmfBuffer() = default;

void DtmfBuffer::Flush() { … }

// The ParseEvent method parses 4 bytes from `payload` according to this format
// from RFC 4733:
//
//  0                   1                   2                   3
//  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |     event     |E|R| volume    |          duration             |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//
// Legend (adapted from RFC 4733)
// - event:    The event field is a number between 0 and 255 identifying a
//             specific telephony event. The buffer will not accept any event
//             numbers larger than 15.
// - E:        If set to a value of one, the "end" bit indicates that this
//             packet contains the end of the event.  For long-lasting events
//             that have to be split into segments, only the final packet for
//             the final segment will have the E bit set.
// - R:        Reserved.
// - volume:   For DTMF digits and other events representable as tones, this
//             field describes the power level of the tone, expressed in dBm0
//             after dropping the sign.  Power levels range from 0 to -63 dBm0.
//             Thus, larger values denote lower volume. The buffer discards
//             values larger than 36 (i.e., lower than -36 dBm0).
// - duration: The duration field indicates the duration of the event or segment
//             being reported, in timestamp units, expressed as an unsigned
//             integer in network byte order.  For a non-zero value, the event
//             or segment began at the instant identified by the RTP timestamp
//             and has so far lasted as long as indicated by this parameter.
//             The event may or may not have ended.  If the event duration
//             exceeds the maximum representable by the duration field, the
//             event is split into several contiguous segments. The buffer will
//             discard zero-duration events.
//
int DtmfBuffer::ParseEvent(uint32_t rtp_timestamp,
                           const uint8_t* payload,
                           size_t payload_length_bytes,
                           DtmfEvent* event) { … }

// Inserts a DTMF event into the buffer. The event should be parsed from the
// bit stream using the ParseEvent method above before inserting it in the
// buffer.
// DTMF events can be quite long, and in most cases the duration of the event
// is not known when the first packet describing it is sent. To deal with that,
// the RFC 4733 specifies that multiple packets are sent for one and the same
// event as it is being created (typically, as the user is pressing the key).
// These packets will all share the same start timestamp and event number,
// while the duration will be the cumulative duration from the start. When
// inserting a new event, the InsertEvent method tries to find a matching event
// already in the buffer. If so, the new event is simply merged with the
// existing one.
int DtmfBuffer::InsertEvent(const DtmfEvent& event) { … }

bool DtmfBuffer::GetEvent(uint32_t current_timestamp, DtmfEvent* event) { … }

size_t DtmfBuffer::Length() const { … }

bool DtmfBuffer::Empty() const { … }

int DtmfBuffer::SetSampleRate(int fs_hz) { … }

// The method returns true if the two events are considered to be the same.
// The are defined as equal if they share the same timestamp and event number.
// The special case with long-lasting events that have to be split into segments
// is not handled in this method. These will be treated as separate events in
// the buffer.
bool DtmfBuffer::SameEvent(const DtmfEvent& a, const DtmfEvent& b) { … }

bool DtmfBuffer::MergeEvents(DtmfList::iterator it, const DtmfEvent& event) { … }

// Returns true if `a` goes before `b` in the sorting order ("`a` < `b`").
// The events are ranked using their start timestamp (taking wrap-around into
// account). In the unlikely situation that two events share the same start
// timestamp, the event number is used to rank the two. Note that packets
// that belong to the same events, and therefore sharing the same start
// timestamp, have already been merged before the sort method is called.
bool DtmfBuffer::CompareEvents(const DtmfEvent& a, const DtmfEvent& b) { … }
}  // namespace webrtc
chromium/third_party/webrtc/modules/audio_coding/neteq/dtmf_buffer.cc
