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Re: Audio recording (using ossaudio)

On 2020-03-14, Yorick Hardy wrote:
> Dear nia,
> On 2020-03-14, nia wrote:
> > On Sat, Mar 14, 2020 at 12:20:11AM +0200, Yorick Hardy wrote:
> > > You are correct. I threw together a NetBSD audio driver based on the oss
> > > driver, but it had exactly the same problem. Strangely, I have been unable to
> > > reproduce the problem on an old i386 netbook (so far).
> > > 
> > > I wrote a test program to try and reproduce what ffmpeg is doing, and
> > > (I am not sure yet) it seems like non-blocking reads is causing the
> > > distortion. The same test program with blocking reads seems to work
> > > okay.
> > > 
> > > I will look into it a bit more, and then report back.
> > 
> > Right, /dev/audio doesn't support non-blocking I/O. But you're supposed to
> > do short enough reads and writes that it shouldn't matter. That might be
> > the cause of the worst of the problems.
> Oops, I think the man page might need to be updated then.
> I managed to convince my test program to correctly record
> with non-blocking I/O (perhaps by accident?) by working
> a bit differently to ffmpeg, but I am not sure how to
> adjust ffmpeg in this way. I will try blocking reads
> (presumably reading blocksize bytes at a time).
> Re: audacity (earlier in the thread), audacity hangs whenever I try to
> record. I probably need to update all of my packages - but I am not
> doing any long builds at the moment due to unpredictable electricity
> supply!
> > Do you want to work on this together somewhere?
> Yes, that would be great! As long as you don't mind someone who is
> extremely unresponsive most of the week! I have quite a few deadlines
> in the next week, and will probably ignore most things while I am
> doing that work.
> Attached are the patches for my "testing" version of the ffmpeg
> backend (heavily based on the OSS backend). I am sure it should be
> renamed to "netbsd", initially I was trying for sun compatibility -
> but I am not sure that makes sense.

Just a side note that I keep forgetting to mention: I used ffmpeg
and oss to record videos over the last few years and "it used to
work fine". I think that the most recent audio changes have
broken some expectations that ffmpeg has, but it used to work
(more or less) as ffmpeg expected.

That said, I think a netbsd audio backend would be great. I will
create a pkgsrc-wip package in the mean time to start working on
a netbsd audio backend, unless someone beats me to it!

[wip/ags also has some audio problems, it uses allegro for audio;
 but I will start another thread about that one day.]

Kind regards,

Yorick Hardy

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