Re: [Alsa-user] Re: audio format TYPE II and TYPE III descriptor support

[Takashi Iwai <tiwai@suse.de>]

At Fri, 9 May 2003 11:11:48 +0200 (CEST),
Jaroslav wrote:
> 
> On Fri, 9 May 2003, Takashi Iwai wrote:
> 
> > At 09 May 2003 09:22:28 +0200,
> > christopher cuse wrote:
> > > 
> > > Good Day,
> > > 
> > > the following is a snip from 
> > > 
> > > /alsa-driver-0.9.3a/alsa-kernel/usb/usbaudio.c
> > > 
> > >        /* FIXME: needed support for TYPE II and III */
> > >         if (format_type != USB_FORMAT_TYPE_I) {
> > >                 snd_printd(KERN_INFO "%d:%u:%d : format type %d is not
> > > supported yet\n",
> > >                            dev->devnum, iface_no, altno, format_type);
> > >                 return -1;
> > >         }
> > > 
> > > 
> > > If a usb card has TYPE II or TYPE III, is there a work around?
> > 
> > my current version already supports these formats but still under
> > debugging.  (also, for using TYPE II, we need a special tool.  the
> > current audio  apps support only linear/float formats.)
> 
> Type II contains MPEG formats?

yes, so far, MPEG (I,II and each layer) and AC3 are defined as the
standard TYPE II.

i'm testing an SB Extigy, which supports AC3.  perhaps a newer version
of Creative's USB device will support MPEG (according to their ad).

for TYPE III, i'm using the normal linear S16_LE.  it's in fact IECxxx
but it's used as 16bit 2 channels.


the support of TYPE II needs, however, still many works.

- MPEG means not only single format but many different ones,
  layer 1-3, MPEG I and II (and later).  use of subformat is necessary
  to distinguish it?  (if we use subformat, snd_pcm_area_xxx needs
  also the argument for subformat..?)

- there is no format defined for AC3 yet.  (SPECIAL is used for
  testing now.)

- moreover, how do we define the "frame size" of the format?
  is it defined as the (alignment of) period size, or the ALSA frame
  bit size?


Takashi


-------------------------------------------------------
Enterprise Linux Forum Conference & Expo, June 4-6, 2003, Santa Clara
The only event dedicated to issues related to Linux enterprise solutions
www.enterpriselinuxforum.com