[Bug 721740] general stream error with alsasink iec958 audio/x-ac3 passtrough

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=721740
  GStreamer | gst-plugins-base | 1.2.2

--- Comment #1 from Daniel Schürmann <daschuer at gmx.de> 2014-01-07 22:07:38 UTC ---
Can one confirm that my command should work? Has one a working setup? 
My original task was playing a DVD with Totem/Pulseaudio and AC3 Sound (Dolby
Digital LED lit on my amp) 
I have also filed an Launchpad bug 
https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/1264609

Currently I have a working mplayer setup with 

pasuspender -- mplayer -mouse-movements -nocache dvdnav:// -ao
alsa:device=iec958=1.0 -ac hwac3

After a lot of investigations, it turns out that there a some problems that
prevents the gst pileline from working, 

1. Passtroug probing fails with -EBUSSY
The alsasink tries to open the same device twice for probing IEC958 parameter. 
IMHO this is not necessary, since the non-audio parameter is just a flag,
defined in the IEC958 standard. So any "spdiff" and "iec958" alsa device is
able to set this flag. Probing for the connected amp capabilities is not
possible because spdiff has no feedback channel. 

2. Generating the device string with parameters fails if the device has already
parameters. alsasink always adds an additional colon this is wrong if there is
already one. 

3. The ac3 stream has 0 channels, this leads to a devision by zero. 

I will prepare a patches for 1 and 2. And I need help to fix 3. Any ideas?

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