Linux: add AudioDeviceLoopbackLinux (OpenAL loopback ADM) by paterkleomenis · Pull Request #22 · desktop-app/lib_webrtc

paterkleomenis · 2026-02-13T22:48:38Z

Summary

Adds a minimal loopback Audio Device Module for Linux that captures system audio output via the OpenAL Soft capture API, by opening the PulseAudio monitor source exposed as an OpenAL capture device.

This is a focused, single-feature PR. It does not include mixing, mic muting, or playback volume control — those are follow-up PRs.

Changes

New files

webrtc/platform/linux/webrtc_loopback_adm_linux.h
webrtc/platform/linux/webrtc_loopback_adm_linux.cpp

Implements AudioDeviceLoopbackLinux (a webrtc::AudioDeviceModule):
- IsSupported() enumerates ALC_CAPTURE_DEVICE_SPECIFIER to detect whether a PulseAudio monitor source is available.
- captureLoop() runs on a dedicated std::thread, reads 10 ms stereo-16 chunks via alcCaptureSamples, and delivers them through webrtc::AudioDeviceBuffer to the WebRTC pipeline.
- Uses the existing desktop-app::external_openal CMake target — no new dependencies.

Modified files

webrtc/webrtc_create_adm.cpp / .h
- CreateLoopbackAudioDeviceModule() now instantiates AudioDeviceLoopbackLinux on Linux (mirrors the existing Windows branch).
- New LoopbackAudioCaptureSupported() function reports whether loopback capture is available on the current platform.
CMakeLists.txt
- Adds the two new source files.
- Adds WEBRTC_LINUX compile definition under elseif (LINUX), matching the existing WEBRTC_WIN / WEBRTC_MAC pattern.

Platform

Linux only. Windows and macOS are unaffected.

Follow-up PRs

Add MixingAudioDeviceModule and loopback mixing transport #26 — Add MixingAudioDeviceModule and loopback mixing transport (depends on this PR)
Add mic-only muting and playback volume control to MixingAudioDeviceModule #24 — Add mic-only muting and playback volume control (depends on Add MixingAudioDeviceModule and loopback mixing transport #26)

ilya-fedin · 2026-02-14T14:03:19Z

CMakeLists.txt


+if (LINUX)
+    find_package(PkgConfig REQUIRED)
+    pkg_check_modules(PIPEWIRE REQUIRED IMPORTED_TARGET libpipewire-0.3)


Why is this change? I don't see pipewire being used anywhere in the code.

You’re right. This pkg_check_modules(PIPEWIRE ...) in lib_webrtc is not needed.
I added it during local Linux bring-up, but lib_webrtc doesn’t directly use PipeWire symbols.
I’ll drop this and keep PipeWire handling in tg_owt/WebRTC.

ilya-fedin · 2026-02-14T22:43:13Z

Squash the commits please

paterkleomenis · 2026-02-14T22:52:45Z

Squash the commits please

Done.

ilya-fedin · 2026-02-16T17:13:35Z

Is the second commit required for audio capture? If not, please make a separate PR

paterkleomenis · 2026-02-22T00:50:56Z

moved to #24

ilya-fedin · 2026-02-22T10:28:17Z

Why? That other PR doesn't seem to contain loopback implementation

paterkleomenis · 2026-02-22T16:56:22Z

Why? That other PR doesn't seem to contain loopback implementation

What do you mean?

ilya-fedin · 2026-02-22T17:03:00Z

I mean I don't understand why this PR is moved. The other PR doesn't seem complete.

ilya-fedin · 2026-02-22T17:14:59Z

That other PR also mixes multiple features in one commit which is a bad thing. All features must be separate PRs, there's a high chance features adding new UI will be rejected (as per tdesktop's CONTRIBUTING.md).

paterkleomenis · 2026-02-22T17:43:15Z

That other PR also mixes multiple features in one commit which is a bad thing. All features must be separate PRs, there's a high chance features adding new UI will be rejected (as per tdesktop's CONTRIBUTING.md).

is it better now?

ilya-fedin · 2026-02-22T17:46:13Z

I still don't understand why we need a new PR... Why couldn't we continue with this one?

paterkleomenis · 2026-02-22T17:48:30Z

i thought you wanted it to be more clean (so there wouldn't be any reason to be rejected)

ilya-fedin · 2026-02-22T18:21:51Z

Okay... If it was just cleanings, you could force push instead of a new PR

Enables the desktop share audio flow on Linux within Calls UI and plumbing. - calls_call: add withAudio parameter to toggleScreenSharing, track _screenWithAudio flag, create/destroy SystemAudioCapture when sharing starts with audio, and clean it up in destroyController. - calls_panel / calls_group_panel: use LoopbackAudioCaptureSupported() to report audio support on all platforms; implement chooseSourceUniqueId() so the chooser can handle single-source (Wayland/PipeWire) mode; open the source chooser when audio is supported instead of bypassing it. - desktop_capture_choose_source: add unique-source mode that skips the screen/window list and shows only the audio toggle + start/stop buttons, used on Linux when a single desktop capture source is pre-selected. Depends on desktop-app/lib_webrtc#22 Closes telegramdesktop#26642

Adds Linux system audio loopback capture support for desktop sharing. This serves as a prerequisite for Linux desktop share audio support in Telegram Desktop. - Added Linux loopback ADM and capture infrastructure (webrtc_loopback_adm_linux, webrtc_loopback_capture_linux, webrtc_system_audio_capture_linux) - Added platform-agnostic SystemAudioCapture interface (webrtc_system_audio_capture) - Wired Linux loopback into webrtc_create_adm (CreateLoopbackAudioDeviceModule, LoopbackAudioCaptureSupported) - Integrated new sources into the build system; removed unused direct PipeWire dependency from CMakeLists

ilya-fedin · 2026-02-22T22:32:56Z

The code is back to what it was... right? What was with the new code, was it completely broken?

paterkleomenis · 2026-02-22T22:34:17Z

The code from pr 24 had replaced the code in pr 22 that was the issue

ilya-fedin · 2026-02-22T22:40:59Z

Maybe I misunderstand something...

You moved this PR to Add mic-only muting and playback volume control to MixingAudioDeviceModule #24
You separated Add mic-only muting and playback volume control to MixingAudioDeviceModule #24 to Linux: add AudioDeviceLoopbackLinux (OpenAL loopback ADM) #25
You moved the code from Linux: add AudioDeviceLoopbackLinux (OpenAL loopback ADM) #25 back to Linux: add AudioDeviceLoopbackLinux (OpenAL loopback ADM) #22
You reverted the code back to what it was before 1

Is this right? If yes, what was the reason for this?

paterkleomenis · 2026-02-22T23:12:41Z

I separated the feature changes per your instructions. Unfortunately the force pushing did not go well initially, so the changes of PR 26 ended up being merged in both PRs 24 and 22.

This has now been fixed, and each change is separately kept in its own PR (although some changes depend on others, for example PR 24 which depends on 26 touches the same files to make extensions to them, so it also includes the code introduced in 26 but shouldn't conflict is 26 is merged first). Git is a mess and i also don't know how to use it well.

john-preston · 2026-02-27T18:56:04Z

Thank you for your work! Let's test that in this implementation, but then I'd like to improve some things, like remove duplication of hardcoded strings for loopback device detection and maybe some more.

Enables the desktop share audio flow on Linux within Calls UI and plumbing. - calls_call: add withAudio parameter to toggleScreenSharing, track _screenWithAudio flag, create/destroy SystemAudioCapture when sharing starts with audio, and clean it up in destroyController. - calls_panel / calls_group_panel: use LoopbackAudioCaptureSupported() to report audio support on all platforms; show a GenericBox with audio toggle when a unique desktop capture source is available (PipeWire), then start sharing with the chosen audio setting. Depends on desktop-app/lib_webrtc#22 Closes telegramdesktop#26642

Enables the desktop share audio flow on Linux within Calls UI and plumbing. - calls_call: add withAudio parameter to toggleScreenSharing, track _screenWithAudio flag, create/destroy SystemAudioCapture when sharing starts with audio, and clean it up in destroyController. - calls_panel / calls_group_panel: use LoopbackAudioCaptureSupported() to report audio support on all platforms; show a GenericBox with audio toggle when a unique desktop capture source is available (PipeWire), then start sharing with the chosen audio setting. Depends on desktop-app/lib_webrtc#22 Closes #26642

ilya-fedin reviewed Feb 14, 2026

View reviewed changes

paterkleomenis force-pushed the linux-share-audio branch from 7894cf9 to 21c5337 Compare February 14, 2026 22:50

This was referenced Feb 14, 2026

Calls: enable audio sharing flow on Linux telegramdesktop/tdesktop#30278

Merged

Calls: fix screenshare audio on mic mute and add incoming volume control telegramdesktop/tdesktop#30293

Open

paterkleomenis force-pushed the linux-share-audio branch from e9dfc0e to 21c5337 Compare February 17, 2026 13:45

paterkleomenis mentioned this pull request Feb 17, 2026

Add mic-only muting and playback volume control to MixingAudioDeviceModule paterkleomenis/lib_webrtc#1

Merged

paterkleomenis closed this Feb 22, 2026

paterkleomenis reopened this Feb 22, 2026

paterkleomenis force-pushed the linux-share-audio branch from 21c5337 to d3e7c62 Compare February 22, 2026 19:43

paterkleomenis changed the title ~~Linux: add system audio capture for desktop sharing~~ Linux: add AudioDeviceLoopbackLinux (OpenAL loopback ADM) Feb 22, 2026

This was referenced Feb 22, 2026

Linux: add AudioDeviceLoopbackLinux (OpenAL loopback ADM) #25

Closed

Add MixingAudioDeviceModule and loopback mixing transport #26

Closed

Add mic-only muting and playback volume control to MixingAudioDeviceModule #24

Open

paterkleomenis force-pushed the linux-share-audio branch from d3e7c62 to e74e30c Compare February 22, 2026 22:17

paterkleomenis force-pushed the linux-share-audio branch from e74e30c to 52faf96 Compare February 22, 2026 22:23

john-preston merged commit 01e1575 into desktop-app:master Feb 27, 2026

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