On Fri, Mar 14, 2008 at 6:57 PM, Eliot Blennerhassett linux@audioscience.com wrote:
On Saturday 15 March 2008 11:35:20 Lee Revell wrote:
On Fri, Mar 14, 2008 at 12:35 AM, Harsha priya gupta
harshapriya@gmail.com 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.
- 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