DTMF Event Sub-API on VoIP API

Added VoipDtmf in VoipEngine as a sub-API to provide DTMF related interfaces; also added relevant unit tests.

Bug: webrtc:11802
Change-Id: Ie9832aebe075a48ae1207be142361b73646673ca
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/180225
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Tim Na <natim@webrtc.org>
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Tim Na <natim@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31974}

api/voip/BUILD.gn

@@ -13,6 +13,7 @@ rtc_source_set("voip_api") {
   sources = [
     "voip_base.h",
     "voip_codec.h",
+    "voip_dtmf.h",
     "voip_engine.h",
     "voip_network.h",
   ]

api/voip/voip_dtmf.h

@@ -0,0 +1,67 @@
+/*
+ *  Copyright (c) 2020 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 API_VOIP_VOIP_DTMF_H_
+#define API_VOIP_VOIP_DTMF_H_
+
+#include "api/voip/voip_base.h"
+
+namespace webrtc {
+
+// DTMF events and their event codes as defined in
+// https://tools.ietf.org/html/rfc4733#section-7
+enum class DtmfEvent : uint8_t {
+  kDigitZero = 0,
+  kDigitOne,
+  kDigitTwo,
+  kDigitThree,
+  kDigitFour,
+  kDigitFive,
+  kDigitSix,
+  kDigitSeven,
+  kDigitEight,
+  kDigitNine,
+  kAsterisk,
+  kHash,
+  kLetterA,
+  kLetterB,
+  kLetterC,
+  kLetterD
+};
+
+// VoipDtmf interface provides DTMF related interfaces such
+// as sending DTMF events to the remote endpoint.
+class VoipDtmf {
+ public:
+  // Register the payload type and sample rate for DTMF (RFC 4733) payload.
+  // Must be called exactly once prior to calling SendDtmfEvent after payload
+  // type has been negotiated with remote.
+  virtual void RegisterTelephoneEventType(ChannelId channel_id,
+                                          int rtp_payload_type,
+                                          int sample_rate_hz) = 0;
+
+  // Send DTMF named event as specified by
+  // https://tools.ietf.org/html/rfc4733#section-3.2
+  // |duration_ms| specifies the duration of DTMF packets that will be emitted
+  // in place of real RTP packets instead.
+  // Must be called after RegisterTelephoneEventType and VoipBase::StartSend
+  // have been called.
+  // Returns true if the requested DTMF event is successfully scheduled.
+  virtual bool SendDtmfEvent(ChannelId channel_id,
+                             DtmfEvent dtmf_event,
+                             int duration_ms) = 0;
+
+ protected:
+  virtual ~VoipDtmf() = default;
+};
+
+}  // namespace webrtc
+
+#endif  // API_VOIP_VOIP_DTMF_H_

api/voip/voip_engine.h

@@ -16,6 +16,7 @@ namespace webrtc {
 class VoipBase;
 class VoipCodec;
 class VoipNetwork;
+class VoipDtmf;
 
 // VoipEngine is the main interface serving as the entry point for all VoIP
 // APIs. A single instance of VoipEngine should suffice the most of the need for
@@ -80,6 +81,9 @@ class VoipEngine {
 
   // VoipCodec provides codec configuration APIs for encoder and decoders.
   virtual VoipCodec& Codec() = 0;
+
+  // VoipDtmf provides DTMF event APIs to register and send DTMF events.
+  virtual VoipDtmf& Dtmf() = 0;
 };
 
 }  // namespace webrtc