Audio Visualizer EventChannel throws MissingPluginException after microphone toggle on Android

[Ebaa-Lau22]

Describe the bug
I'm using the LiveKit Flutter SDK audio visualizer feature on Android. Initially, the waveform visualization works fine, but after toggling the microphone off and back on, the waveform stops animating and the following error appears in the logs:

MissingPluginException(No implementation found for method listen on channel io.livekit.audio.visualizer/eventChannel)

This error causes the waveform animation to stop, though the rest of the audio functionality continues working.
To Reproduce

1. Run the app on Android device or emulator with LiveKit Flutter SDK (version = 2.4.6).
2. Start the audio visualizer (waveform) and verify it works.
3. Toggle the microphone off.
4. Toggle the microphone back on.
5. Observe the MissingPluginException and that the waveform stops updating.

Expected behavior

The audio visualizer's native EventChannel stream should properly restart or continue streaming after toggling the microphone, without throwing MissingPluginException.

Platform information

• Flutter version: 3.29.3
• Plugin version: 2.4.6
• Flutter target OS: Android 35

Thank you!

[phanbaohuy96]

Any update? I got the same issue on:

• flutter: 3.32.8
• livekit_client: ^2.5.0+hotfix.1
• iOS: 18.6

[bdlukaa]

It is related to ryanheise/just_audio#274.

I found the cause of this problem: stopping then disposing. Before disposing, stop should not be called.

client-sdk-flutter/example/lib/widgets/sound_waveform.dart

Lines 87 to 88 in 70d4d1f

	await _visualizer?.stop();
	await _visualizer?.dispose();

I removed await _visualizer?.dispose(); and it fixed the issue.

[bdlukaa]

Now, a different issue appears (listen):

══╡ EXCEPTION CAUGHT BY SERVICES LIBRARY
The following MissingPluginException was thrown while activating platform stream on channel 
io.livekit.audio.visualizer/eventChannel-TR_AMtp8vjzaF8N2j-5db8a338-5ba9-4b32-bd0e-e1aae19ae436: 
MissingPluginException(No implementation found for method listen on channel 
io.livekit.audio.visualizer/eventChannel-TR_AMtp8vjzaF8N2j-5db8a338-5ba9-4b32-bd0e-e1aae19ae436)

When the exception was thrown, this was the stack:
#0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:365:7)
<asynchronous suspension>
#1      EventChannel.receiveBroadcastStream.<anonymous closure> (package:flutter/src/services/platform_channel.dart:712:11)
<asynchronous suspension>

May be related:

• No implementation found for method listen on channel FlutterWebRTC.Method & FlutterWebRTC.Event flutter-webrtc/flutter-webrtc#1424

[bdlukaa]

It looks like we should keep await _visualizer?.stop(); and remove await _visualizer?.dispose(); to properly close streams.