[alsa-devel] Passing audio info from HDMI EDID beside speaker allocation
Hi Takashi,
You proposed snd_pcm_query_chmaps() to query underlying hardware speaker allocation. Please correct me if I have wrong understanding of this API. On the other hand, HDMI EDID contains audio data other than speaker allocation such as audio formats(LPCM, AC3, and etc). How are these information other than speaker allocation passed back to the user-space? Are there a standard kernel and alsa query interfaces now?
Thanks Patrick
On 10/4/2012 11:50 PM, Patrick Lai wrote:
Hi Takashi,
You proposed snd_pcm_query_chmaps() to query underlying hardware speaker allocation. Please correct me if I have wrong understanding of this API. On the other hand, HDMI EDID contains audio data other than speaker allocation such as audio formats(LPCM, AC3, and etc). How are these information other than speaker allocation passed back to the user-space? Are there a standard kernel and alsa query interfaces now?
Thanks Patrick
Does anyone else have feedback for my query to Takashi?
At Thu, 04 Oct 2012 23:50:20 -0700, Patrick Lai wrote:
Hi Takashi,
You proposed snd_pcm_query_chmaps() to query underlying hardware speaker allocation. Please correct me if I have wrong understanding of this API. On the other hand, HDMI EDID contains audio data other than speaker allocation such as audio formats(LPCM, AC3, and etc). How are these information other than speaker allocation passed back to the user-space? Are there a standard kernel and alsa query interfaces now?
In the case of HD-audio, it's passed via the normal IEC958 status bits controls separately. ELD itself is exposed as a byte array in a control element, but it's read-only.
Takashi
On 10/8/2012 1:20 AM, Takashi Iwai wrote:
In the case of HD-audio, it's passed via the normal IEC958 status bits controls separately. ELD itself is exposed as a byte array in a control element, but it's read-only.
Thanks for the reply. Couple more questions
1. Is kcontrol "ELD" being read directly by application or there is ALSA library API to parse the information.
2. Also, I see you submit this patch [PATCH 3/3] ELD proc interface for HDMI sinks in 2008. I presume it's just for information purpose. You still expect application to query for HDMI sink capability through "ELD" kcontrol. Am I correct?
Takashi
At Mon, 22 Oct 2012 11:00:02 -0700, Patrick Lai wrote:
On 10/8/2012 1:20 AM, Takashi Iwai wrote:
In the case of HD-audio, it's passed via the normal IEC958 status bits controls separately. ELD itself is exposed as a byte array in a control element, but it's read-only.
Thanks for the reply. Couple more questions
- Is kcontrol "ELD" being read directly by application or there is
ALSA library API to parse the information.
Nothing so far. It's just a raw data.
- Also, I see you submit this patch [PATCH 3/3] ELD proc interface for
HDMI sinks in 2008. I presume it's just for information purpose. You still expect application to query for HDMI sink capability through "ELD" kcontrol. Am I correct?
It's not prohibited for apps to parse the proc interface but it's not guaranteed to be stable :) So yes, parsing ELD manually would be a safer way.
Takashi
In the case of HD-audio, it's passed via the normal IEC958 status bits controls separately. ELD itself is exposed as a byte array in a control element, but it's read-only.
Thanks for the reply. Couple more questions
- Is kcontrol "ELD" being read directly by application or there is
ALSA library API to parse the information.
Nothing so far. It's just a raw data.
- Also, I see you submit this patch [PATCH 3/3] ELD proc interface for
HDMI sinks in 2008. I presume it's just for information purpose. You still expect application to query for HDMI sink capability through "ELD" kcontrol. Am I correct?
It's not prohibited for apps to parse the proc interface but it's not guaranteed to be stable :) So yes, parsing ELD manually would be a safer way.
I wrote some code to parse the ELD kcontrol to enable passthrough if AC3 is supported by the receiver, I believe it's been integrated by Arun in a branch of PulseAudio. It's probably 1 year old now..
participants (3)
-
Patrick Lai -
Pierre-Louis Bossart -
Takashi Iwai