fix(ios): auto-fallback from PCM to MP3 for ElevenLabs TTS

leepokai · claude · leepokai · commit fbc26ef9f3d5 · 2026-03-02T02:32:12.000+08:00
The default output format pcm_44100 requires an ElevenLabs Pro tier
subscription. Users on free or starter plans get a silent 403 failure
and hear no audio.

Instead of hardcoding mp3, keep pcm_44100 as the default (better
quality for Pro users) but remember the failure: when a PCM request
is rejected, set pcmFormatUnavailable and use mp3_44100_128 for all
subsequent requests in the session. The flag resets on config reload
so it re-probes after reconnection.

Also standardize the MP3 fallback format from mp3_44100 to
mp3_44100_128 for consistent bitrate.

Co-Authored-By: Claude Opus 4.6 &lt;noreply@anthropic.com&gt;
diff --git a/apps/ios/Sources/Voice/TalkModeManager.swift b/apps/ios/Sources/Voice/TalkModeManager.swift
@@ -72,6 +72,9 @@ final class TalkModeManager: NSObject {
     private var mainSessionKey: String = "main"
     private var fallbackVoiceId: String?
     private var lastPlaybackWasPCM: Bool = false
+    /// Set when the ElevenLabs API rejects PCM format (e.g. 403 subscription_required).
+    /// Once set, all subsequent requests in this session use MP3 instead of re-trying PCM.
+    private var pcmFormatUnavailable: Bool = false
     var pcmPlayer: PCMStreamingAudioPlaying = PCMStreamingAudioPlayer.shared
     var mp3Player: StreamingAudioPlaying = StreamingAudioPlayer.shared
 
@@ -1004,7 +1007,8 @@ final class TalkModeManager: NSObject {
                 let desiredOutputFormat = (directive?.outputFormat ?? self.defaultOutputFormat)?
                     .trimmingCharacters(in: .whitespacesAndNewlines)
                 let requestedOutputFormat = (desiredOutputFormat?.isEmpty == false) ? desiredOutputFormat : nil
-                let outputFormat = ElevenLabsTTSClient.validatedOutputFormat(requestedOutputFormat ?? "pcm_44100")
+                let outputFormat = ElevenLabsTTSClient.validatedOutputFormat(
+                    requestedOutputFormat ?? self.effectiveDefaultOutputFormat)
                 if outputFormat == nil, let requestedOutputFormat {
                     self.logger.warning(
                         "talk output_format unsupported for local playback: \(requestedOutputFormat, privacy: .public)")
@@ -1051,8 +1055,9 @@ final class TalkModeManager: NSObject {
                     self.lastPlaybackWasPCM = true
                     var playback = await self.pcmPlayer.play(stream: stream, sampleRate: sampleRate)
                     if !playback.finished, playback.interruptedAt == nil {
-                        let mp3Format = ElevenLabsTTSClient.validatedOutputFormat("mp3_44100")
+                        let mp3Format = ElevenLabsTTSClient.validatedOutputFormat("mp3_44100_128")
                         self.logger.warning("pcm playback failed; retrying mp3")
+                        self.pcmFormatUnavailable = true
                         self.lastPlaybackWasPCM = false
                         let mp3Stream = client.streamSynthesize(
                             voiceId: voiceId,
@@ -1388,7 +1393,7 @@ final class TalkModeManager: NSObject {
 
     private func resolveIncrementalPrefetchOutputFormat(context: IncrementalSpeechContext) -> String? {
         if TalkTTSValidation.pcmSampleRate(from: context.outputFormat) != nil {
-            return ElevenLabsTTSClient.validatedOutputFormat("mp3_44100")
+            return ElevenLabsTTSClient.validatedOutputFormat("mp3_44100_128")
         }
         return context.outputFormat
     }
@@ -1474,7 +1479,8 @@ final class TalkModeManager: NSObject {
         let desiredOutputFormat = (directive?.outputFormat ?? self.defaultOutputFormat)?
             .trimmingCharacters(in: .whitespacesAndNewlines)
         let requestedOutputFormat = (desiredOutputFormat?.isEmpty == false) ? desiredOutputFormat : nil
-        let outputFormat = ElevenLabsTTSClient.validatedOutputFormat(requestedOutputFormat ?? "pcm_44100")
+        let outputFormat = ElevenLabsTTSClient.validatedOutputFormat(
+            requestedOutputFormat ?? self.effectiveDefaultOutputFormat)
         if outputFormat == nil, let requestedOutputFormat {
             self.logger.warning(
                 "talk output_format unsupported for local playback: \(requestedOutputFormat, privacy: .public)")
@@ -1525,6 +1531,11 @@ final class TalkModeManager: NSObject {
             latencyTier: TalkTTSValidation.validatedLatencyTier(context.directive?.latencyTier))
     }
 
+    /// Returns `mp3_44100_128` when the API has already rejected PCM, otherwise `pcm_44100`.
+    private var effectiveDefaultOutputFormat: String {
+        self.pcmFormatUnavailable ? "mp3_44100_128" : "pcm_44100"
+    }
+
     private static func makeBufferedAudioStream(chunks: [Data]) -> AsyncThrowingStream<Data, Error> {
         AsyncThrowingStream { continuation in
             for chunk in chunks {
@@ -1580,8 +1591,9 @@ final class TalkModeManager: NSObject {
             var playback = await self.pcmPlayer.play(stream: stream, sampleRate: sampleRate)
             if !playback.finished, playback.interruptedAt == nil {
                 self.logger.warning("pcm playback failed; retrying mp3")
+                self.pcmFormatUnavailable = true
                 self.lastPlaybackWasPCM = false
-                let mp3Format = ElevenLabsTTSClient.validatedOutputFormat("mp3_44100")
+                let mp3Format = ElevenLabsTTSClient.validatedOutputFormat("mp3_44100_128")
                 let mp3Stream = client.streamSynthesize(
                     voiceId: voiceId,
                     request: self.makeIncrementalTTSRequest(
@@ -1991,6 +2003,7 @@ extension TalkModeManager {
             self.gatewayTalkDefaultModelId = nil
             self.gatewayTalkApiKeyConfigured = false
             self.gatewayTalkConfigLoaded = false
+            self.pcmFormatUnavailable = false
         }
     }
 
