feat: mic passthrough via VB-Audio Virtual Cable

[xenstalker02]

Summary

Adds encrypted client microphone passthrough to the Windows host during a streaming session. Mic audio routes through VB-Audio Virtual Cable — no Steam Remote Play session required, always active.

How it works

• Vibelight (client) captures mic via SDL, Opus-encodes at 96kbps mono
• Sends as 0x3003 packets over the existing encrypted control stream (SS_ENC_CONTROL_V2)
• Vibepollo decodes Opus → writes PCM to CABLE Input via WASAPI (speaker_wasapi_t)
• Windows routes CABLE Input → CABLE Output automatically
• Session start: switches Windows default capture to CABLE Output so Discord (set to Default) picks up the mic automatically
• Session end: restores previous default capture device (e.g. AT2040)

No manual Discord configuration needed. Encrypted sessions only — plaintext mic is refused.

Requirements (host)

• VB-Audio Virtual Cable installed

Client

Pairs with xenstalker02/Vibelight — a Moonlight fork with SDL2 mic capture, Opus encoding, and stereo-to-mono downmix for PipeWire compatibility.

Relation to Logan's PR #1428 on ClassicOldSong/Apollo

Logan's implementation uses a dedicated UDP port negotiated via RTSP with LiSendMicrophoneOpusDataEx (requires a fork of moonlight-common-c) and renders to Steam Streaming Microphone. That approach requires an active Steam Remote Play session to activate the loopback.

This implementation reuses the existing encrypted control stream transport (no moonlight-common-c changes, no new UDP port) and VB-Cable (always-active loopback). Both approaches are valid — this one has fewer dependencies.

Files changed

• src/stream.cpp — IDX_MIC_AUDIO_DATA handler, per-session Opus decoder, jitter buffer, FEC/PLC, session init/teardown
• src/platform/windows/audio.cpp — speaker_wasapi_t WASAPI render client, virtual_microphone(), VB-Cable device lookup
• src/config.h / src/config.cpp — mic_sink, mic_capture_device config options
• Web UI strings (en.json, Troubleshooting.vue), README

Testing

Validated end-to-end: mic packets received, decoded, written to CABLE Input, audible in Discord on host. Tested on LAN and over Tailscale. Per-session stats (packets, PLC, decode errors, latency) logged every 30s.

[xenstalker02]

Closing — feature/mic-passthrough-vbcable has been fully absorbed into master via rebase. The PR diff is now empty (feature branch is identical to master). A clean upstream PR has been opened at Nonary/Vibepollo#168 using a properly scoped branch (upstream-pr/mic-passthrough) based on Nonary's upstream/master.