From 8b73c31faea543fa3fcd62be244a98455c8ba0af Mon Sep 17 00:00:00 2001
From: zztkm <zztkm@tsurutatakumi.info>
Date: Thu, 12 Sep 2024 18:44:35 +0900
Subject: [PATCH] =?UTF-8?q?Answer=20=E3=81=AE=20SDP=20=E3=82=92=E6=9B=B8?=
 =?UTF-8?q?=E3=81=8D=E6=8F=9B=E3=81=88=E3=82=8B=E5=87=A6=E7=90=86=E3=82=92?=
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---
 Sora/Configuration.swift |  3 +++
 Sora/PeerChannel.swift   | 32 ++++++++++++++++++++++++++++++--
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/Sora/Configuration.swift b/Sora/Configuration.swift
index 72e8c426..fa4c9d99 100644
--- a/Sora/Configuration.swift
+++ b/Sora/Configuration.swift
@@ -215,6 +215,9 @@ public struct Configuration {
     /// 通常、指定する必要はありません。
     public var publisherAudioTrackId: String = defaultPublisherAudioTrackId
 
+    /// ステレオ出力を許可するための設定です。
+    public var forceStereoOutput: Bool = false
+
     /**
      初期化します。
 
diff --git a/Sora/PeerChannel.swift b/Sora/PeerChannel.swift
index 6c33f7f6..a912a2f4 100644
--- a/Sora/PeerChannel.swift
+++ b/Sora/PeerChannel.swift
@@ -577,7 +577,6 @@ class PeerChannel: NSObject, RTCPeerConnectionDelegate {
 
         Logger.debug(type: .peerChannel, message: "try create answer")
         Logger.debug(type: .peerChannel, message: offer)
-
         Logger.debug(type: .peerChannel, message: "try setting remote description")
         let offer = RTCSessionDescription(type: .offer, sdp: offer)
         nativeChannel.setRemoteDescription(offer) { error in
@@ -689,7 +688,36 @@ class PeerChannel: NSObject, RTCPeerConnectionDelegate {
                 return
             }
 
-            let answer = SignalingAnswer(sdp: sdp!)
+            var sdp = sdp!
+
+            // Chrome/Edge 向けのハック stereo=1 が CreateOffer では付与されないので、
+            // SDP を書き換えて stereo=1 を付与する
+            // https://github.com/w3c/webrtc-stats/issues/686
+            // https://github.com/w3c/webrtc-extensions/issues/63
+            // https://issues.webrtc.org/issues/41481053#comment18
+            if (self.configuration.forceStereoOutput) {
+                Logger.debug(type: .peerChannel, message: "stereo=1 を付与する")
+                let pattern = "minptime=\\d+"
+                let regexp = try! NSRegularExpression(pattern: pattern)
+                let replacementFunc: (String) -> String = { match in
+                    if !match.contains("stereo=1") {
+                        return "\(match);stereo=1"
+                    }
+                    return match
+                }
+
+                let matches = regexp.matches(in: sdp, range: NSRange(sdp.startIndex..., in: sdp))
+                for match in matches.reversed() {
+                    print("kensaku: match: \(match)")
+                    let range = match.range
+                    let matchedString = (sdp as NSString).substring(with: range)
+                    let replacedString = replacementFunc(matchedString)
+                    print("kensaku: replacedString: \(replacedString)")
+                    sdp = (sdp as NSString).replacingCharacters(in: range, with: replacedString)
+                }
+            }
+
+            let answer = SignalingAnswer(sdp: sdp)
             self.signalingChannel.send(message: Signaling.answer(answer))
             self.lock.unlock()
             Logger.debug(type: .peerChannel, message: "did send answer")