mirror of
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227 lines
8.6 KiB
C++
227 lines
8.6 KiB
C++
/*
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* Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "webrtc/modules/audio_coding/neteq/dtmf_buffer.h"
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#include <assert.h>
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#include <algorithm> // max
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// Modify the code to obtain backwards bit-exactness. Once bit-exactness is no
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// longer required, this #define should be removed (and the code that it
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// enables).
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#define LEGACY_BITEXACT
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namespace webrtc {
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// The ParseEvent method parses 4 bytes from |payload| according to this format
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// from RFC 4733:
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//
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// 0 1 2 3
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// 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
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | event |E|R| volume | duration |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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//
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// Legend (adapted from RFC 4733)
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// - event: The event field is a number between 0 and 255 identifying a
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// specific telephony event. The buffer will not accept any event
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// numbers larger than 15.
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// - E: If set to a value of one, the "end" bit indicates that this
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// packet contains the end of the event. For long-lasting events
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// that have to be split into segments, only the final packet for
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// the final segment will have the E bit set.
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// - R: Reserved.
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// - volume: For DTMF digits and other events representable as tones, this
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// field describes the power level of the tone, expressed in dBm0
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// after dropping the sign. Power levels range from 0 to -63 dBm0.
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// Thus, larger values denote lower volume. The buffer discards
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// values larger than 36 (i.e., lower than -36 dBm0).
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// - duration: The duration field indicates the duration of the event or segment
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// being reported, in timestamp units, expressed as an unsigned
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// integer in network byte order. For a non-zero value, the event
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// or segment began at the instant identified by the RTP timestamp
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// and has so far lasted as long as indicated by this parameter.
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// The event may or may not have ended. If the event duration
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// exceeds the maximum representable by the duration field, the
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// event is split into several contiguous segments. The buffer will
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// discard zero-duration events.
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//
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int DtmfBuffer::ParseEvent(uint32_t rtp_timestamp,
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const uint8_t* payload,
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int payload_length_bytes,
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DtmfEvent* event) {
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if (!payload || !event) {
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return kInvalidPointer;
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}
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if (payload_length_bytes < 4) {
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return kPayloadTooShort;
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}
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event->event_no = payload[0];
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event->end_bit = ((payload[1] & 0x80) != 0);
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event->volume = (payload[1] & 0x3F);
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event->duration = payload[2] << 8 | payload[3];
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event->timestamp = rtp_timestamp;
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return kOK;
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}
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// Inserts a DTMF event into the buffer. The event should be parsed from the
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// bit stream using the ParseEvent method above before inserting it in the
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// buffer.
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// DTMF events can be quite long, and in most cases the duration of the event
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// is not known when the first packet describing it is sent. To deal with that,
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// the RFC 4733 specifies that multiple packets are sent for one and the same
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// event as it is being created (typically, as the user is pressing the key).
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// These packets will all share the same start timestamp and event number,
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// while the duration will be the cumulative duration from the start. When
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// inserting a new event, the InsertEvent method tries to find a matching event
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// already in the buffer. If so, the new event is simply merged with the
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// existing one.
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int DtmfBuffer::InsertEvent(const DtmfEvent& event) {
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if (event.event_no < 0 || event.event_no > 15 ||
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event.volume < 0 || event.volume > 36 ||
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event.duration <= 0 || event.duration > 65535) {
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return kInvalidEventParameters;
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}
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DtmfList::iterator it = buffer_.begin();
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while (it != buffer_.end()) {
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if (MergeEvents(it, event)) {
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// A matching event was found and the new event was merged.
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return kOK;
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}
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++it;
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}
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buffer_.push_back(event);
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// Sort the buffer using CompareEvents to rank the events.
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buffer_.sort(CompareEvents);
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return kOK;
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}
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bool DtmfBuffer::GetEvent(uint32_t current_timestamp, DtmfEvent* event) {
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DtmfList::iterator it = buffer_.begin();
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while (it != buffer_.end()) {
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// |event_end| is an estimate of where the current event ends. If the end
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// bit is set, we know that the event ends at |timestamp| + |duration|.
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uint32_t event_end = it->timestamp + it->duration;
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#ifdef LEGACY_BITEXACT
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bool next_available = false;
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#endif
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if (!it->end_bit) {
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// If the end bit is not set, we allow extrapolation of the event for
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// some time.
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event_end += max_extrapolation_samples_;
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DtmfList::iterator next = it;
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++next;
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if (next != buffer_.end()) {
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// If there is a next event in the buffer, we will not extrapolate over
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// the start of that new event.
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event_end = std::min(event_end, next->timestamp);
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#ifdef LEGACY_BITEXACT
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next_available = true;
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#endif
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}
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}
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if (current_timestamp >= it->timestamp
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&& current_timestamp <= event_end) { // TODO(hlundin): Change to <.
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// Found a matching event.
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if (event) {
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event->event_no = it->event_no;
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event->end_bit = it->end_bit;
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event->volume = it->volume;
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event->duration = it->duration;
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event->timestamp = it->timestamp;
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}
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#ifdef LEGACY_BITEXACT
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if (it->end_bit &&
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current_timestamp + frame_len_samples_ >= event_end) {
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// We are done playing this. Erase the event.
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buffer_.erase(it);
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}
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#endif
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return true;
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} else if (current_timestamp > event_end) { // TODO(hlundin): Change to >=.
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// Erase old event. Operation returns a valid pointer to the next element
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// in the list.
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#ifdef LEGACY_BITEXACT
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if (!next_available) {
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if (event) {
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event->event_no = it->event_no;
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event->end_bit = it->end_bit;
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event->volume = it->volume;
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event->duration = it->duration;
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event->timestamp = it->timestamp;
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}
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it = buffer_.erase(it);
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return true;
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} else {
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it = buffer_.erase(it);
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}
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#else
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it = buffer_.erase(it);
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#endif
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} else {
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++it;
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}
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}
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return false;
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}
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int DtmfBuffer::SetSampleRate(int fs_hz) {
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if (fs_hz != 8000 &&
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fs_hz != 16000 &&
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fs_hz != 32000 &&
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fs_hz != 48000) {
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return kInvalidSampleRate;
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}
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max_extrapolation_samples_ = 7 * fs_hz / 100;
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frame_len_samples_ = fs_hz / 100;
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return kOK;
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}
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// The method returns true if the two events are considered to be the same.
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// The are defined as equal if they share the same timestamp and event number.
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// The special case with long-lasting events that have to be split into segments
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// is not handled in this method. These will be treated as separate events in
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// the buffer.
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bool DtmfBuffer::SameEvent(const DtmfEvent& a, const DtmfEvent& b) {
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return (a.event_no == b.event_no) && (a.timestamp == b.timestamp);
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}
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bool DtmfBuffer::MergeEvents(DtmfList::iterator it, const DtmfEvent& event) {
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if (SameEvent(*it, event)) {
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if (!it->end_bit) {
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// Do not extend the duration of an event for which the end bit was
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// already received.
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it->duration = std::max(event.duration, it->duration);
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}
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if (event.end_bit) {
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it->end_bit = true;
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}
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return true;
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} else {
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return false;
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}
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}
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// Returns true if |a| goes before |b| in the sorting order ("|a| < |b|").
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// The events are ranked using their start timestamp (taking wrap-around into
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// account). In the unlikely situation that two events share the same start
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// timestamp, the event number is used to rank the two. Note that packets
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// that belong to the same events, and therefore sharing the same start
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// timestamp, have already been merged before the sort method is called.
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bool DtmfBuffer::CompareEvents(const DtmfEvent& a, const DtmfEvent& b) {
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if (a.timestamp == b.timestamp) {
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return a.event_no < b.event_no;
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}
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// Take wrap-around into account.
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return (static_cast<uint32_t>(b.timestamp - a.timestamp) < 0xFFFFFFFF / 2);
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}
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} // namespace webrtc
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