From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tanu Kaskinen Subject: Re: [RFC] Channel mapping API (take 2) Date: Wed, 05 Sep 2012 09:38:26 +0300 Message-ID: <1346827106.3629.40.camel@laptop> References: <1346824812.3629.29.camel@laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from out1-smtp.messagingengine.com (out1-smtp.messagingengine.com [66.111.4.25]) by alsa0.perex.cz (Postfix) with ESMTP id 0DD932652F8 for ; Wed, 5 Sep 2012 08:38:29 +0200 (CEST) In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: Takashi Iwai Cc: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org On Wed, 2012-09-05 at 08:17 +0200, Takashi Iwai wrote: > Well, this raises a question "What is mono". > If this is supposed to be a channel position, then we should add the > definition. But is it really so? If it's a mono stream mixed from > front left and front right, isn't it a front center? If it's a playback stream and alsa knows that it will be routed to a center speaker on a surround system, then yes, it should be front center. But if the audio ends up in a lone speaker, mixing left and right doesn't really result in a center position. I think mono means pretty much "single channel without defined position", for which SND_CHMAP_UNKNOWN could be a useful choice, except that I think PulseAudio will end up ignoring channels with SND_CHMAP_UNKNOWN, because there's no sane definition for how channel remapping should be done for such channels. But maybe the single channel case could be treated as an exception - a single channel with SND_CHMAP_UNKNOWN could be treated as a mono device, for which downmixing (or upmixing in case of capture) is well defined. -- Tanu