[pulseaudio-discuss] [PATCH RESEND] alsa-sink: Don't pretend to support passthrough on HDMI surround sinks

Alexander E. Patrakov patrakov at gmail.com
Fri Nov 27 04:30:38 PST 2015

It doesn't work currently (fails and falls back to PCM), due to channel
count mismatch between the sink sample spec and the sample spec required
by IEC61937.

To be reverted when someone implements changing channel count without
switching profiles. This would also be required for HBR passthrough over

Reported-by: Xamindar <junkxamindar at gmail.com>
Signed-off-by: Alexander E. Patrakov <patrakov at gmail.com>
 src/modules/alsa/alsa-sink.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/modules/alsa/alsa-sink.c b/src/modules/alsa/alsa-sink.c
index c5a72c3..2fdebe0 100644
--- a/src/modules/alsa/alsa-sink.c
+++ b/src/modules/alsa/alsa-sink.c
@@ -2226,7 +2226,13 @@ pa_sink *pa_alsa_sink_new(pa_module *m, pa_modargs *ma, const char*driver, pa_ca
             pa_log_info("Disabling latency range changes on underrun");
-    if (is_iec958(u) || is_hdmi(u))
+    /* All passthrough formats supported by PulseAudio require
+     * IEC61937 framing with two fake channels. So, passthrough
+     * clients will always send two channels. Multichannel sinks
+     * cannot accept that, because nobody implemented sink channel count
+     * switching so far. So just don't show known non-working settings
+     * to the user. */
+    if ((is_iec958(u) || is_hdmi(u)) && ss.channels == 2)
         set_formats = true;
     u->rates = pa_alsa_get_supported_rates(u->pcm_handle, ss.rate);

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