Description of problem:

QEMU Remote Audio via VNC stopped working around april 2012 in various Fedora version.

It was discovered that a new configure option "--enable-mixemu" was used in qemu-1.0-15.fc1x.src.rpm that inadvertently hit a bug in QEMU. This was not noticed primiliary because there are very few VNC clients that implement the QEMU AUDIO RFB protocol extensions.

I only discovered the bug after my own VNC client stopped working when I upgraded from QEMU 0.13 (Fedora 14) to QEMU 1.1.x.

Version-Release number of selected component (if applicable):

Fedora 16, 17 or any version using > qemu-1.0-10.fcx

How reproducible:

Steps to Reproduce:
1. Install Fedora 16 as a Host
2. Create a guest that can produce sound (e.g. Windows XP)
3. Using a QEMU AUDIO RFB capable VNC client, connect to the guest and capture sound. Such a client can be found here:

http://repo.or.cz/w/qemu-vcap.git

Actual results:

Silence.

Expected results:

Sound reproduction.

Additional info:

I original reported this to the QEMU mailing list, details can be found here:
http://lists.gnu.org/archive/html/qemu-devel/2012-07/msg01814.html

A patch was produced that fixes the issue as follows:

[..snip..]

diff --git a/audio/audio.c b/audio/audio.c
index 583ee51..1c77389 100644
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -818,6 +818,7 @@ static int audio_attach_capture (HWVoiceOut *hw)
         sw->active = hw->enabled;
         sw->conv = noop_conv;
         sw->ratio = ((int64_t) hw_cap->info.freq << 32) / sw->info.freq;
+        sw->vol = nominal_volume;
         sw->rate = st_rate_start (sw->info.freq, hw_cap->info.freq);
         if (!sw->rate) {
             dolog ("Could not start rate conversion for `%s'\n", SW_NAME (sw));

[..snip..]

Adding the patch to qemu-1.0-15.fc1x.src.rpm as well as the latest rawhide versions and testing confirmed that this patch fixes the problem for all versions.

It should be noted that you can avoid the bug by not using the --enable-mixemu configure option too.