From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eliot Blennerhassett Subject: Re: basic questions Date: Sat, 15 Mar 2008 11:57:38 +1300 Message-ID: <200803151157.38835.linux@audioscience.com> References: <827ad74d0803132135i6c7c8ad8sa7ad5469cc677920@mail.gmail.com> <75b66ecd0803141535g66aae270v5c53fb67e973566f@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp3.clear.net.nz (smtp3.clear.net.nz [203.97.33.64]) by alsa0.perex.cz (Postfix) with ESMTP id 6B9B61037F0 for ; Fri, 14 Mar 2008 23:52:31 +0100 (CET) Received: from zaphod (121-72-250-62.cable.telstraclear.net [121.72.250.62]) by smtp3.clear.net.nz (CLEAR Net Mail) with ESMTP id <0JXQ00HH6SVF7G40@smtp3.clear.net.nz> for alsa-devel@alsa-project.org; Sat, 15 Mar 2008 11:52:29 +1300 (NZDT) In-reply-to: <75b66ecd0803141535g66aae270v5c53fb67e973566f@mail.gmail.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: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org 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. regards -- Eliot Blennerhassett www.audioscience.com