Re: [sweep-devel] Working on a Jack output driver

[pete s. <ps_...@la...>]

On Fri, 2010-01-01 at 15:36 +1100, Erik de Castro Lopo wrote:
> torbenh wrote:
> 
> > at least the original patch i did was just playback. 
> > i dont know if kickback added record. 
> 
> Well there is a read as well as a write so it might have been
> added by kickback.

if there's a functioning jack input, i didn't add it. i may have
added skeleton functions to the driver though. 
it's been a long time since i looked at sweep i'm afraid and i'm a
little sketchy on the details.

> > the basic problem is that record is happening in a separate thread.
> 
> I don't think that necessarily has to be the case.
> 
> > another weak point was that the driver is only opened when the user hit
> > play for the first time. 
> 
> The version in SVN now seems to open the JACK driver at program startup,
> but that makes it really difficult to change drivers at run time which is
> something I have just got running in the trunk.

perhaps i'm missing the subtleties here, but can't we just add some
extra hooks to the driver api for this? i added some to init the driver
at startup IIRC. it's just a matter of updating the old drivers with
redundant entries to match the new api. ie some kind of driver
shutdown/cleanup function that stops play/rec?. i'm not aware of any
third party drivers with which we need to maintain backwards
compatibility. failing that, perhaps mandate a restart in order to
effect a change of driver. at least then the driver isn't dictated by
the distro for many people.

> I don't think there is an easy fix fo this. It seems that the way JACK 
> works doesn't fit very well witht the way an application like sweep 
> works.

another problem occurs when using samples that don't match the jack
sample rate. sweep relies on the device driver to resample to the device
rate normally, using a low quality (but fast) resampler to handle
varispeed and scrubbing. the resampler sounds bad, even to my dull ears
and we can't really use this for normal playback of files that don't
match a mandated sample rate, yet jack offers no resampler at all. 
this means we need another resampler for the jack driver, else we
require people to resample all their files offline to match the jack
sample rate.

cheers,
pete.