Hi,
first of all, I've never contributed to the xine project, and
I don't have any experience with sndio, so bear with me...
Frustrated with the bad sound playing a 6 channels aac audio I decided to
take a look. The device is a usb one:
$ dmesg | grep -i audio
uaudio0 at uhub2 port 3 configuration 1 interface 1 "GeneralPlus USB Audio
Device" rev 1.10/1.00 addr 6
uaudio0: class v1, full-speed, sync, channels: 2 play, 1 rec, 8 ctls
audio0 at uaudio0
uhidev2 at uhub2 port 3 configuration 1 interface 3 "GeneralPlus USB Audio
Device" rev 1.10/1.00 addr 6
It has only 2 channels for playback.
The file has 5.1 aac audio:
$ ffprobe file.mp4
[...]
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 224
kb/s (default)
[...]
Xine's ffmpegaudio plugin is supposed to do downmix (please, correct
me if I'm wrong), but:
$ xine --verbose=2 file.mp4
[...]
audio_out: ao_open (0x585415540)
audio_sndio_out: ao_sndio_open bits=16 rate=48000, mode=128
audio_sndio_out: ao_sndio_open 6 channels output
[...]
The code in xine-lib-1.2.12/src/audio_out/audio_sndio_out.c by Brad
Smith is following the recommendations at sio_open(3), there is no
problem there.
sio_getpar() is returning 6 channels as valid, so the sound ends
messed up. The right speaker gets mostly ambient sound and the
voices are almost only audible through the left speaker.
mplayer and mpv have means to force downmix, but xine is the only
media player which can play 1080p h264 video with a decent performance
(if the bitrate is not too high) on an rpi4 (no hardware acceleration,
cpu at 2.2Gz)
One workaround for this particular case could be adding the
configuration setting "audio.output.speaker_arrangement" to
audio_sndio_out.c.
I'm using the last snapshot:
$ doas sysupgrade -ns
Fetching from https://ftp.OpenBSD.org/pub/OpenBSD/snapshots/arm64/
SHA256.sig 100% |************************************************| 1544 00:00
Signature Verified
Already on latest snapshot.
base72.tgz 21-Sep-2022 11:41 262659517
Is this behaviour normal and I'm just missing something?
Some thoughts?
