[pulseaudio-discuss] Alsa -> pulseaudio 24-bit playback support for hardware that doesn't support 24 bits

[Baek Chang]

I can't seem to resolve this issue in ALSA/pulseaudio where playing S24_LE
pcm data does not seem to work.  My hardware does not support 24 bits, but I
was under the impression that alsa would do a conversion to 32 bits when
using -D plug.


I get the following errors:

aplay -D plug:pulse test-sound-files/sine_1kHz_24bit_stereo_44kHz.wav -vvvv
Playing WAVE 'test-sound-files/sine_1kHz_24bit_stereo_44kHz.wav' : Signed 24
bit Little Endian in 3bytes, Rate 44100 Hz, Stereo
*aplay: set_params:1022: Unable to install hw params:*
ACCESS:  RW_INTERLEAVED
FORMAT:  S24_3LE
SUBFORMAT:  STD
SAMPLE_BITS: 24
FRAME_BITS: 48
CHANNELS: 2
RATE: 44100
PERIOD_TIME: 125000
PERIOD_SIZE: (5512 5513)
PERIOD_BYTES: (33072 33078)
PERIODS: (3 5)
BUFFER_TIME: 500000
BUFFER_SIZE: 22050
BUFFER_BYTES: 132300
TICK_TIME: 0

Using this device works with ALSA:

aplay -D plug:hw:0 test-sound-files/sine_1kHz_24bit_stereo_44kHz.wav -vvvv
Playing WAVE 'test-sound-files/sine_1kHz_24bit_stereo_44kHz.wav' : Signed 24
bit Little Endian in 3bytes, Rate 44100 Hz, Stereo
Plug PCM: Linear conversion PCM (S16_LE)

Also using paplay works as well:

paplay test-sound-files/sine_1kHz_24bit_stereo_44kHz.wav -vvvv
Using sample spec 'float32le 2ch 44100Hz'
Connection established.
Stream successfully created

Is there a problem with the intermediary step between ALSA and pulseaudio?
It seems that ALSA will do linear pcm conversion, when the hardware does not
support 24 bits when using -D plug, but does not seem to work when routing
to pulseaudio.  Is this a bug in the ALSA/pulseaudio plugin?

Baek
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