AC3 - SPDIF Passthrough - Pulseaudio - Karmic 9.10

[Wyv]

Hello,

This isn't a request for assistance, just a tip as I didn't see much else for SPDIF passthrough and Karmic.

When I upgraded to 9.10 from 9.04 my SPDIF passthrough was no longer working.

In 9.04 I would use Pulseaudio for everything but DD or DTS audio. All sound would still go over SPDIF. I had SMPlayer set up to directly access the SPDIF hardware device for AC3 or DTS.

In 9.10 this doesn't directly work; using the cool new hardware chooser to use your hardware setup in Preferences > Sounds Pulsaudio can now output to your SPDIF without you messing with conf files. However, it seems to keep the device (SPDIF) busy and so when an app tries to access it directly it won't work.

What I have to do is to open Preference > Sounds and choose something without IEC958 SPDIF in the hardware section. Then play my DD or DTS audio with the player set to use the ALSA device directly and SPDIF passthrough.

Then, after watching the movie I have to set it back so that Pulseaudio can use the SPDIF output again.

Tip: Opening and making changes in Preferences > Sound mutes audio often, making you think stuff is broken. You'll need to unmute it in the mixer in the system tray or use gnome alsa-mixer or summat.

It would be great if Pulseaudio could handle assigning a DD stream to a SPDIF device directly.

[lloydsmart]

Thank you! This explains why I couldn't get DD or DTS soundtracks to work, I tried disabling the hdmi sound in hardware selector as you suggested, and bingo! I'm getting bitstreamed DD/DTS over HDMI from XBMC.

My big problem now, is that I need some way to automate this. I have a mixture of media, some of which requires DD/DTS bitstreaming, and thus requires the HDMI to be disabled in the hardware selector, and some which comes in other sound formats such as MP3, FLAC, etc. which requires the HDMI to be on and working in the hardware selector.

Is there any way to get the HDMI in the hardware selector to automatically switch depending on what you're trying to play? I don't want to have to quit and relaunch XBMC every time I want to play DD/DTS!

Thanks.

[Wyv]

None that I know of

If you're just using XBMC maybe it's worth looking at removing Pulseaudio.

nb: I actually quite like PA, but the inability to do anything useful with DD / DTS passthrough sucks. I wanna use the DACs in my receiver and also not have 95 cables connecting it

[lloydsmart]

Hmm... I guess I need to read up on what PulseAudio actually is, as XBMC isn't the only thing I use this computer for at the moment (although that was the intention when I built it, but I no longer have a laptop for other duties, so...)

What else does PA do? I need the sound to work generally in Ubuntu, such as system sounds, Youtube, VLC, etc. Plus it would be nice if it continued to work in games. All these functions currently work fine over the HDMI. Would they continue to do so if I removed PA?

If so, my next question would be: how does one go about removing PA, and could there be any other side effects?

Thanks!

[Wyv]

Pulseaudio is sound server; it takes all of the audio streams from applications, does mixing, volume control etc and then sends audio to particular sound devices.

You can remove it and just use ALSA and hardware mixing. There are guides around for removing PA and setting up an ALSA based system. ALSA is still used behind PA as it manages the sound hardware - you'd just be stripping PA off of the top of it.

I personally prefer to keep PA, but the SPDIF passthrough thing is really irritating - especially now as PA is hogging the output device.

[lloydsmart]

especially now as PA is hogging the output device.

Right, this is exactly the issue causing problems, I think.

What we need is some way to have pulseaudio automatically step back and disable itself when we attempt to play an AC3 or DTS soundtrack. Does anyone have any idea how something like this could be achieved?

[Wyv]

I'm not aware of one - nothing obvious from searching for it.

The official RFE is here, not updated in 16 months: http://www.pulseaudio.org/ticket/167

With the increasing use of computers (and Linux) for home theatres this strikes me as core functionality.

[lekzz]

Passthrough is working for me, however playing normal (non-passthrough) audio seems to "mute" passthrough. Pressing mute and unmute makes passthrough work again.
This "mute" is also not showing in alsa-mixer, as everything is set like it should. But then again it's passthrough.

example after reboot:
open movie with passthrough - audio works
close movie
open movie with mp3 - audio works
close movie
open movie with passthrough - no audio
while movie open mute/unmute - audio works again

This happened during one of the last updates before 9.10 final, as i was running 9.10 from alpha6 and had no problems until just before the final.

[lloydsmart]

This is almost the same on my system. I'm running the 9.10 release, but I don't get passthrough by default after reboot, which I think is down to the fact that I'm using the Ubuntu system sounds, e.g. the noise that plays when you login, etc.

If I go to Preferences -> Sound, I can "turn off" sound ,which means that no normal stereo stuff plays, but passthrough works. Only problem with this is that I can't play anything with "non-passthrough" sound.

This is why I asked about some sort of automation. There must be something that can be set so that when a "passthrough" track is played, it turns off all other sound so that it works, then when a "normal" track is played, it uses PulseAudio again. I just don't know how to do it.

[Wyv]

I believe that's going to need something written / coded - which is beyond me

I'm not aware of anything that could detect the DD or DTS bitstream attempting to be passed through. I'm assuming if it were easy to do the Pulseaudio would have the ability to detect when it is given a DD / DTS stream and then pass that through unaltered to the output device.