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ao_alsa: add ridiculous hack to deal with braindead ALSA behavior

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dmix reports channel layouts it doesn't support. The rest of the
technical part of the story is in the code comment.

This seems to be the only reasonable way to fallback from trying to
initialize certain devices (like dmix) with multichannel audio. We could
probably add support for such padding channels to our audio chain or to
ao_alsa itself, but this would probably be much more work than this
commit.

What dmix does is probably a bug. I've tried to report it to ALSA. Thay
have a link on their website to a bug tracker, but it's a dead link, and
has been for years. I've posted to alsa-devel, but received no reply.
I'm thus assuming this absolutely retarded behavior is by design, and
nothing will happen to improve upon it.

I'm considering sending Lennart Poettering a "thank you" email, because
with PulseAudio, multichannel audio just works (although some other
things just don't work).
This commit is contained in:
wm4 2014-12-15 16:40:17 +01:00
parent 756adee999
commit ae5fd4a809
1 changed files with 42 additions and 3 deletions
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45
audio/out/ao_alsa.c
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@ -440,7 +440,10 @@ static void uninit(struct ao *ao)
alsa_error: ;
}
static int init(struct ao *ao)
#define INIT_OK 0
#define INIT_ERROR -1
#define INIT_BRAINDEATH -2
static int init_device(struct ao *ao)
{
struct priv *p = ao->priv;
int err;
@ -621,6 +624,34 @@ static int init(struct ao *ao)
MP_WARN(ao, "ALSA channel map conflicts with channel count!\n");
}
} else {
// Is it one that contains NA channels?
struct mp_chmap chmap2 = {0};
for (int c = 0; c < alsa_chmap->channels; c++) {
int alsa_ch = alsa_chmap->pos[c];
if (alsa_ch != SND_CHMAP_NA)
chmap2.speaker[chmap2.num++] = find_mp_channel(alsa_ch);
}
if (mp_chmap_is_valid(&chmap2)) {
// Sometimes, ALSA will advertise certain chmaps, but it's not
// possible to set them. This can happen with dmix: as of
// alsa 1.0.28, dmix can do stereo only, but advertises the
// surround chmaps of the underlying device. In this case,
// requesting e.g. 5.1 will fail, but it will still allow
// setting 6 channels. Then it will return something like
// "FL FR NA NA NA NA" as channel map. This means we would
// have to pad stereo output to 6 channels with silence, which
// is way too complicated in the general case. You can't change
// the number of channels to 2 either, because the hw params
// are already set! So just fuck it and reopen the device with
// the chmap "cleaned out" of NA entries.
err = snd_pcm_close(p->alsa);
p->alsa = NULL;
CHECK_ALSA_ERROR("pcm close error");
ao->channels = chmap2;
return INIT_BRAINDEATH;
}
MP_WARN(ao, "Got unknown channel map from ALSA.\n");
}
@ -675,11 +706,19 @@ static int init(struct ao *ao)
p->can_pause = snd_pcm_hw_params_can_pause(alsa_hwparams);
return 0;
return INIT_OK;
alsa_error:
uninit(ao);
return -1;
return INIT_ERROR;
}
static int init(struct ao *ao)
{
int r = init_device(ao);
if (r == INIT_BRAINDEATH)
r = init_device(ao); // retry with normalized channel layout
return r == INIT_OK ? 0 : -1;
}
static void drain(struct ao *ao)