[MPlayer-users] hwac3 with 5.1 on old nforce 220D s/pdif gives stereo only

[Dominique Dumont]

Michael Holland <mplayer at golden.wattle.id.au> writes:

> I'm using an old Asus A7N266-VM motherboard for a HTPC, and cannot get
> surround sound from the digital audio out. This has the nVidia 220D
> nforce-1 chip with dolby digital.
>   I don't know if the dolby-encoding is supposed to work under Linux,
> but figure I should be able to simply pipe the AC3 from a DVD or digital
> TV straight out the s/pdif for decoding in the amp?

Here's my experience with Nforce2 with also feature a dolby digital
encoder.

DD encoding works only with nvsound driver, not with Alsa because
Nvidia never gaves the spec, and the guy able to do some reverse
engeneering never got the HW.

For simple DD output, I've found that you can get DD signal out of the
SPDIF output, but it's flagged as audio not data, so some decoder
(like my Yamaha A1) refuses to decode it.

See https://bugtrack.alsa-project.org/alsa-bug/view.php?id=411 for details.


> I'm using Ubuntu, which auto-configured the sound. I think
> snd_intel8x0 is the driver.  By fiddling with alsamixer, I enabled
> analog 5.1 out, and the s/pdif out.

I also use snd_intel8x0 with Nforce2.

> $ mplayer  -ac hwac3 -vo null sample,dvd,ac3-5.1.avi
> Forced audio codec: hwac3
> Opening audio decoder: [hwac3] AC3/DTS pass-through S/PDIF
> No accelerated IMDCT transform found
> hwac3: switched to AC3, 448000 bps, 48000 Hz
> AUDIO: 48000 Hz, 2 ch, ac3, 448.0 kbit/29.17% (ratio: 56000->192000)
> Selected audio codec: [hwac3] afm: hwac3 (AC3 through S/PDIF)
>
> Why is it cutting to 2 channels?

I'd say that the AC3 stream is stereo. Check with 'file' command.

> If I leave out the "-ac hwac3", I get correct decoding to the analogue.
>
> Should I be using the 'nvsound' binary driver? That seems to be
> OSS-only, not ALSA.

It's indeed OSS.

> Please - point me in the right direction. Not sure what I need to
> learn here. Is this an mplayer problem, or my ALSA setup, or shouldn't
> I be using ALSA at all?

Sorry I can't help you more that advising to buy a 25 Euros sound card
like I did (DD and DTS output work without problem with my Creative
Sound blaster digital live 5.1).

HTH (but I doubt it)