Audio

Configure sound output and microphone input redirection in FreeRDP, including codecs and audio backends.

Overview

FreeRDP supports redirecting audio in both directions:

• Sound output (/sound) — plays audio from the remote session on the local client.
• Microphone input (/microphone) — captures audio on the client and sends it to the remote session.

Both features are implemented as virtual channels (rdpsnd for output, audin for input) and are negotiated with the server at connect time.

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Build requirements

Audio backends

FreeRDP supports the following platform audio backends. At least one must be available.

Backend	CMake flag	Platform
ALSA	-DWITH_ALSA=ON (default)	Linux
PulseAudio	-DWITH_PULSE=ON (default)	Linux
OSS	-DWITH_OSS=ON (default)	Linux / BSD
sndio	Available when sndio headers are present	OpenBSD / FreeBSD
CoreAudio	Built-in	macOS
WinMM	Built-in	Windows

Audio codecs

The most widely supported codec is uncompressed PCM, which requires no additional libraries. Compressed codecs improve quality and reduce bandwidth.

Codec	Build flag	Notes
PCM	Always available	Uncompressed, zero configuration
AAC	-DWITH_FAAC=ON / -DWITH_FAAD2=ON	Best quality; AAC encoding requires -DWITH_DSP_EXPERIMENTAL=ON
GSM	-DWITH_GSM=ON	Older low-bandwidth codec
FFmpeg codecs	-DWITH_DSP_FFMPEG=ON	Enables FFmpeg-based encode/decode pipeline
SOXR resampling	-DWITH_SOXR=ON	Optional resampling library

AAC is the preferred compressed codec for Windows 8 and newer servers. To enable AAC encoding (client-to-server microphone), you must also pass -DWITH_DSP_EXPERIMENTAL=ON at build time.

Example build with PulseAudio and FFmpeg:

cmake -GNinja \
  -DCMAKE_BUILD_TYPE=Release \
  -DWITH_PULSE=ON \
  -DWITH_DSP_FFMPEG=ON \
  -B build -S .
cmake --build build --target install

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Sound output

Enable sound redirection with the /sound flag.

# Enable sound with default backend
xfreerdp /sound /v:rdp.example.com

# Specify the ALSA backend explicitly
xfreerdp /sound:sys:alsa /v:rdp.example.com

# Specify OSS with a device and format
xfreerdp /sound:sys:oss,dev:1,format:1 /v:rdp.example.com

# Use PulseAudio
xfreerdp /sound:sys:pulse /v:rdp.example.com

Sound sub-options

Sub-option	Example	Description
sys:<backend>	sys:alsa	Select the audio backend (alsa, pulse, oss)
dev:<device>	dev:1	Select a specific device index
format:<n>	format:1	Select a specific audio format index

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Microphone input

Enable microphone redirection with the /microphone flag.

# Enable microphone with default backend
xfreerdp /microphone /v:rdp.example.com

# Specify ALSA
xfreerdp /microphone:sys:alsa /v:rdp.example.com

# Specify OSS with a device
xfreerdp /microphone:sys:oss,dev:1,format:1 /v:rdp.example.com

The /microphone option accepts the same sys:, dev:, and format: sub-options as /sound.

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Using both simultaneously

xfreerdp /sound:sys:pulse /microphone:sys:pulse /v:rdp.example.com

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Troubleshooting

No audio heard after connecting

• Confirm the build includes an audio backend: check for rdpsnd-client-pulse.so or rdpsnd-client-alsa.so in the plugin directory.

• On Linux with PulseAudio, ensure the PulseAudio daemon is running: pulseaudio --check.

• On Linux with ALSA, verify the device is not muted: alsamixer.

• Enable debug logging to trace the codec negotiation:

  WLOG_LEVEL=DEBUG xfreerdp /sound /v:rdp.example.com 2>&1 | grep -i rdpsnd
  

Microphone not working

• Ensure the build includes audin channel support with the correct backend.
• On Linux, check that the input device is not muted and is set as the default capture device.
• The server must support the Audio Input virtual channel (audin). Verify it is not blocked by group policy on the server.

Poor audio quality or high latency

• PCM is uncompressed and uses the most bandwidth. If bandwidth is limited, ensure a compressed codec (AAC or GSM) was negotiated. Check the debug log for the negotiated format.
• Rebuild with -DWITH_DSP_FFMPEG=ON or -DWITH_FAAD2=ON to enable compressed codec support.
• Consider enabling SOXR resampling (-DWITH_SOXR=ON) to improve sample rate conversion quality.

AAC codec not available

• AAC encoding requires -DWITH_FAAC=ON and -DWITH_DSP_EXPERIMENTAL=ON.
• AAC decoding requires -DWITH_FAAD2=ON or -DWITH_DSP_FFMPEG=ON.
• Rebuild with the appropriate flags and verify the codec appears in the negotiation log.