[mythtv] [Fwd: Re: [mythtv-users] Your soundcard is not reporting free space correctly.]

Ann Patterson annp322 at sbcglobal.net
Mon Mar 8 11:15:04 EST 2004

-----Forwarded Message-----
> From: Ann Patterson <annp322 at sbcglobal.net>
> To: Discussion about mythtv <mythtv-users at mythtv.org>
> Subject: Re: [mythtv-users] Your soundcard is not reporting free space correctly.
> Date: Tue, 02 Mar 2004 08:02:03 -0800
> On Sun, 2004-02-22 at 19:51, Ann Patterson wrote:
> > I have had a myth box set up and working nicely for some time, using
> > myth 0.14, FC1, and Jarod's instructions. Today, I put a new sound card
> > into the box, a M-Audio Revolution 7.1 (ice1724 alsa driver). I have
> > alsa installed, and except for mythtv, the new sound card works fine.
> > Mythmusic, mplayer, and everything else I've tried is fine. But when I
> > try to either watch live tv, or play recordings that I recorded before I
> > put the new card in, I get no sound at all, and the following error
> > repeatedly from the frontend:
> > 
> > Your soundcard is not reporting free space correctly. 
> > Falling back to old method...
> > 
> <snip>
> I'll respond to my own post. After doing some debugging, it turns out
> that, indeed, my soundcard is *not* reporting free space correctly.
> Mplayer and Xine work because both use a different method than myth for
> syncing video and sound. The alsa folks are looking at it now. I'll post
> again when it's fixed. 

After even more debugging, and a reading of the OSS docs, I discovered
that the values returned from ioctl(audio_fd, SNDCTL_DSP_GETOSPACE,
&info) are undefined if you're not writing full fragments to the card.
For every other card I tested, the values returned from this call were
fine, even when writing partial fragments. But when I ran this with the
M-Audio card, the values are all over the place. I was able to duplicate
the problem with the alsa osstest program, writing blocks of 1000 bytes.
When I changed the osstest program to write 4096 bytes (this card's
fragsize), the problem went away.

I can take a crack at fixing this, but I don't really understand the
syncing with video works. Someone who understands this code better may
stand a better chance of fixing the problem without creating new

Ann P.

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