[gst-devel] [Fwd: Re: [oss-devel] [Correction] libgstoss4audio / SNDCTL_MIX_READ]

Clive Wright clive_wright at ntlworld.com
Thu May 8 22:58:09 CEST 2008

Reply from Hannu Savolainen [oss-devel] to my earlier posting about
gstreamer plugin for OSS4 in gst-plugins-bad

Clive Wright kirjoitti:
> The recently added gstreamer plugin for OSS4 has problems handling the
> value returned by SNDCTL_MIX_READ for control type MIXT_MONOSLIDER16
> (and I suspect MIXT_MONOSLIDER).
> See attached extract of oss4_mixer.log
> This appears to be caused by stereo values being returned by
> SNDCTL_MIX_READ for these control types.
> The OSS v4 Programmer's guide is not explicit in this situation stating
> only that:
> "The current value of the mixer control will be returned in the value
> field".
Unfortunately there was some syntax error in the source file for the
manual page for SNDCTL_MIX_EXTINFO and almost everything on that page
was cut off. Anyway now the
http://manuals.opensound.com/developer/SNDCTL_MIX_EXTINFO.html page
contains links to the pages for all the MIXT_ types. The encoding of the
value field is defined there.

In short:

MIXT_SLIDER is 31 bit positive integer.
MIXT_MONOSLIDER is 8 bit positive integer (0xVV)
MIXT_MONOSLIDER is 16 bit positive integer (0xVVVV).
MIXT_STEREOSLIDER is a pair of 8 bit positive integers (0xRRLL)
MIXT_STEREOSLIDER16 is a pair of 16 bit positive integers (0xRRRRLLLL).
Both LLLL and RRRR limited to 0..32767 range.

Best regards,

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