SRT AAC audio channel corruption when switching from stereo to mono

Which version are you using?

v1.21.0_windows_amd64

Which operating system are you using?

Windows amd64 standard

Describe the issue

1. I Start a Moblin stream using a DJI camera's microphone.
2. The DJI microphone produces stereo audio.
3. I Route the stream through MediaMTX via SRT to OBS.
4. I Switch Moblin from the DJI microphone to the iPhone internal microphone.
5. The iPhone internal microphone produces mono audio.
6. The left channel continues to contain the correct iPhone microphone audio, but the right channel becomes heavily corrupted/noisy. OBS continues to show the stream as having two audio channels.

The corruption is deterministic: it happens every time when starting on the DJI microphone and switching to the internal microphone.

The reverse transition does NOT cause the problem. If I start Moblin on the iPhone internal microphone (mono). and then switch between the internal microphone and DJI microphone back and fort, no problem occurs.

The volume level of the corrupted right channel appears to depend on the audio level at the moment of switching. For example, if the iPhone microphone is quiet when switching, the corruption is quiet. If I blow into the iPhone microphone during the transition, the corrupted signal is much louder.

Without MediaMTX in the path, the problem does not occur.

Here is a clip about the issue happening during the stream [VOLUME WARNING] https://www.twitch.tv/acourierslife/clip/RamshackleFrozenOxSuperVinlin-kwlChi04ERe5tBzc?range=7d

• I started the stream using the DJI's mic.
• Battery run out so I changed it
• Switched back to IRL scene too early
• DJI wasn't available yet so Moblin used the iPhone's mic
• MediaMTX mishandled the stereo to mono switch.

[This report was originally produced by an LLM then slightly modified by me. I'm no expert on the topic]

Describe how to replicate the issue

1. Start a Moblin stream using a DJI camera's microphone.
2. Route the stream through MediaMTX via SRT to OBS
3. Switch Moblin from the DJI microphone to the iPhone internal microphone.
4. Right channel gets messed up in OBS

MediaMTX configuration

MediaMTX logs

No response

Packet dump

No response