From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Lee Revell" Subject: Re: basic questions Date: Mon, 17 Mar 2008 22:01:34 -0400 Message-ID: <75b66ecd0803171901k17ed767dj30f6e4f79e25857e@mail.gmail.com> References: <827ad74d0803132135i6c7c8ad8sa7ad5469cc677920@mail.gmail.com> <75b66ecd0803141535g66aae270v5c53fb67e973566f@mail.gmail.com> <200803151157.38835.linux@audioscience.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from rv-out-0910.google.com (rv-out-0910.google.com [209.85.198.189]) by alsa0.perex.cz (Postfix) with ESMTP id D92D5243A4 for ; Tue, 18 Mar 2008 03:01:35 +0100 (CET) Received: by rv-out-0910.google.com with SMTP id k20so4476483rvb.32 for ; Mon, 17 Mar 2008 19:01:34 -0700 (PDT) In-Reply-To: <200803151157.38835.linux@audioscience.com> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: Eliot Blennerhassett Cc: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org On Fri, Mar 14, 2008 at 6:57 PM, Eliot Blennerhassett wrote: > On Saturday 15 March 2008 11:35:20 Lee Revell wrote: > > On Fri, Mar 14, 2008 at 12:35 AM, Harsha priya gupta > > > > wrote: > > > Hi, > > > > > > I am ramping up on ALSA architecture and framework. I have a couple of > > > basic questions. I apologize if these questions are very basic to be > > > raised in this mailing list. If anyone can help me find answers, it would > > > be great. Thanks in advance. > > > > > > 1. My assumption is that ALSA handles only PCM streams today. Does it > > > handle encoded streams from application to sound card (Which can do > > > hardware decoding)? > > > > Someone else could probably give a better answer, but I believe that > > currently ALSA has no API for cards that do HW decoding. > > Not AFAIK, and certainly the architecture assumes a constant data rate. I.e X > bytes consumed implies elapsed time of (X * constant) = the _period_ > > Alsa headers do define some format constants for compressed audio. > > We would like to support compressed audio for our cards, which can do hardware > decoding. I did try to implement it early on, but got lost in the quagmire of > driver midlevel code and alsa-lib. > > A first step would be to allow CBR compressed formats to pass through to the > driver unaltered. For these there is a defined bits per sample, though it can > be non-integer which might be a problem. I would look at how ALSA implements AC3 passthrough. Lee