HDMI Audio Support in ALSA

HDMI Audio Support in ALSA

[Kallol Biswas]

Hi,
   We are building a HDMI capture card that has a HDMI audio device.

The audio device needs to be integrated with ALSA framework.
Unfortunately the audio is not supported in ALSA.

I understand that work is being done at this moment to support the audio format.

Any information on when the support will be available is helpful.

Kallol

Senior Software Engineer
NucleoDyne System, Inc.
19925 Stevens Creek Blvd
Cupertino, CA 95014

Re: HDMI Audio Support in ALSA

[Lee Revell]

On Mon, May 19, 2008 at 12:04 PM, Kallol Biswas <nucleodyne@gmail.com> wrote:
> Hi,
>   We are building a HDMI capture card that has a HDMI audio device.
>
> The audio device needs to be integrated with ALSA framework.
> Unfortunately the audio is not supported in ALSA.
>
> I understand that work is being done at this moment to support the audio format.
>
> Any information on when the support will be available is helpful.

You don't provide nearly enough information.  What exactly is missing
from ALSA that you need?

Normally if you develop a new device you must write a (GPL'ed) ALSA
driver for it.

Lee

Re: HDMI Audio Support in ALSA

[Kallol Biswas]

Can ALSA handle HDMI audio frames? It does not look so.

Do you need a pointer to HDMI audio spec (L-PCM, IEC 60958 IEC 61937 etc.)?

On 5/19/08, Lee Revell <rlrevell@joe-job.com> wrote:
> On Mon, May 19, 2008 at 12:04 PM, Kallol Biswas <nucleodyne@gmail.com> wrote:
>  > Hi,
>  >   We are building a HDMI capture card that has a HDMI audio device.
>  >
>  > The audio device needs to be integrated with ALSA framework.
>  > Unfortunately the audio is not supported in ALSA.
>  >
>  > I understand that work is being done at this moment to support the audio format.
>  >
>  > Any information on when the support will be available is helpful.
>
>
> You don't provide nearly enough information.  What exactly is missing
>  from ALSA that you need?
>
>  Normally if you develop a new device you must write a (GPL'ed) ALSA
>  driver for it.
>
>
>  Lee
>

Re: HDMI Audio Support in ALSA

[Clemens Ladisch]

(please don't top-post)

Kallol Biswas wrote:
> Can ALSA handle HDMI audio frames? It does not look so.

Why do you think so?

> Do you need a pointer to HDMI audio spec (L-PCM, IEC 60958 IEC 61937 etc.)?

L-PCM is linear PCM, which is the sample format used by practically
_every_ sound card.  IEC 60958 is AES/EBU, which is essentially S/PDIF,
which uses linear PCM samples.  IEC 61937 specifies how to transport
compressed streams over S/PDIF, by pretending the data stream is a
sequence of linear PCM samples.

All of this is supported by ALSA.


Regards,
Clemens

Re: HDMI Audio Support in ALSA

[Clemens Ladisch]

(please don't top-post!)

Kallol Biswas wrote:
> I am looking at 2.6.25.4 kernel source code. The header file pcm.h
> does not have any definition for supporting IEC 60958 or IEC 61937 frame types.

Almost all S/PDIF transmitters/receivers use SNDRV_PCM_FORMAT_S16.
(Some use S32 for 24-bit samples, but this doesn't matter for
IEC 60958/61937.)

> However, SNDRV_PCM_FMTBIT_IEC958_SUBFRAME is supported.

This is only for some early revisions of the CMI8738 chip which require
software to generate the preamble/channel status/subcode/parity bits
for each subframe.


Regards,
Clemens

Re: HDMI Audio Support in ALSA

[Takashi Iwai]

At Thu, 22 May 2008 14:36:13 +0200,
Clemens Ladisch wrote:
> 
> > However, SNDRV_PCM_FMTBIT_IEC958_SUBFRAME is supported.
> 
> This is only for some early revisions of the CMI8738 chip which require
> software to generate the preamble/channel status/subcode/parity bits
> for each subframe.

Some ATIIXP boards need it, too.  HD-audio controllers can do also
this kind of things, but not needed.


Takashi

Re: HDMI Audio Support in ALSA

[Kallol Biswas]

Hello Takashi,
                   I have been reading the pci/hda code, and now not
sure if I have the answer to my original question.

The routine snd_hda_calc_stream_format() calls snd_pcm_format_width()
to find if the format is supported and the width.

The array holds pcm_format[] holds all the supported formats. However,
in this array
there is no entry for IEC 60958 or IEC 61937. How does it work? How
does the hda code
handles the above frames?

It seems that snd_hda_calc_stream_format() is going to print "invalid
format width < val>" for HDMI audio frames.

Kallol

On 5/23/08, Takashi Iwai <tiwai@suse.de> wrote:
> At Thu, 22 May 2008 14:36:13 +0200,
>
> Clemens Ladisch wrote:
>  >
>  > > However, SNDRV_PCM_FMTBIT_IEC958_SUBFRAME is supported.
>  >
>  > This is only for some early revisions of the CMI8738 chip which require
>  > software to generate the preamble/channel status/subcode/parity bits
>  > for each subframe.
>
>
> Some ATIIXP boards need it, too.  HD-audio controllers can do also
>  this kind of things, but not needed.
>
>
>
>  Takashi
>

Re: HDMI Audio Support in ALSA

[Clemens Ladisch]

Kallol Biswas wrote:
> The routine snd_hda_calc_stream_format() calls snd_pcm_format_width()
> to find if the format is supported and the width.
>
> The array holds pcm_format[] holds all the supported formats. However,
> in this array
> there is no entry for IEC 60958 or IEC 61937.

There is.  I already told you that these formats use
SNDRV_PCM_FORMAT_S16_LE.


Regards,
Clemens

Re: HDMI Audio Support in ALSA

[Takashi Iwai]

At Mon, 26 May 2008 09:16:15 +0200,
Clemens Ladisch wrote:
> 
> Kallol Biswas wrote:
> > The routine snd_hda_calc_stream_format() calls snd_pcm_format_width()
> > to find if the format is supported and the width.
> >
> > The array holds pcm_format[] holds all the supported formats. However,
> > in this array
> > there is no entry for IEC 60958 or IEC 61937.
> 
> There is.  I already told you that these formats use
> SNDRV_PCM_FORMAT_S16_LE.

Yes.  The apps usually sends the raw data as S16_LE to the driver.
In addition, we have status bits controls.  These are stored into a
control element, and thus independently handled from the raw data.

With SNDRV_PCM_FORMAT_IEC958_SUBFRAME format, both the raw and the
status bits are composed together.  But, which format is supported
depends purely on the driver.


Takashi