From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
To: alsa-devel@alsa-project.org
Subject: Re: Can ASoC support SPDIF AC3 passthrough playback (non linear PCM) ?
Date: Mon, 23 Jul 2012 14:36:49 -0500 [thread overview]
Message-ID: <500DA7D1.7060507@linux.intel.com> (raw)
In-Reply-To: <500CA2F2.1090801@gmail.com>
On 7/22/2012 8:03 PM, Gabriel M. Beddingfield wrote:
> On 07/21/2012 10:39 AM, Sangsu Park wrote:
>> Hi,
>> We're developing a platform where we have SPDIF output.
>> And we want to SPDIF AC3 playback (non linear PCM).
>> Our CPU is a kind of ARM architecture one and it has a SPDIF that can
>> support AC3 passthrough playback.
>>
>> I've already know that ALSA can support SPDIF AC3 passthrough playback
>> like follows,
>> http://www.mythtv.org/wiki/Configuring_Digital_Sound_with_AC3_and_SPDIF
>> But, I can't find that any ARM architecture CPU can be supportable for
>> SPDIF AC3 passthrough playback.
>>
>> Are there anyone who have a SPDIF AC3 passthrough playback?
>> or anyone who know the clue about SPDIF AC3 passthrought playback
>> supportable on ASoC?
>
> I'm currently working on a similar project -- and I'm learning about
> this myself, too.
>
> As I understand it, you have to package the AC-3 into IEC 61937 format
> first. The S/PDIF driver will then encode it into the IEC 60958
> (S/PDIF protocol).
>
> You probably need/want a copy of IEC 61937-3.[1] It looks pretty
> simple (add 4 headers to the front and some zero-padding at the end to
> meet the alignment requirements). I don't know of any software
> examples for doing it[2] -- so if you find some, please share! :-)
>
> As for feeding it to ALSA, I think that's what the
> SNDRV_PCM_FORMAT_IEC958_SUBFRAME is intended for. However, in
> practice I've heard that you can usually configure the PCM device to
> something like an S16 format and things "just work." (IEC 61937-3's
> payload is 16-bit aligned.)
>
> ...and I think I've heard of some people shooting raw AC-3 and things
> "just work." YMMV. :-)
There are two modes really
- one where you send 16-bit data with the 61937 format. somehow the
hardware add the preambles and CUVP bits
- one where you create the complete 32-bit frame using the iec958
alsa-lib plugin
Both work with my HDAudio output, the latter is more flexible if you
want to set the C/U bits
Note that this is all supported in PulseAudio, and gstreamer can package
AC3/DTS data for you. mplayer also does.
-Pierre
prev parent reply other threads:[~2012-07-23 19:36 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-21 15:39 Can ASoC support SPDIF AC3 passthrough playback (non linear PCM) ? Sangsu Park
2012-07-22 18:42 ` Mark Brown
2012-07-23 1:03 ` Gabriel M. Beddingfield
2012-07-23 13:41 ` Sangsu Park
2012-07-23 19:36 ` Pierre-Louis Bossart [this message]
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