Hi, Am Sonntag, 14. Oktober 2007 schrieb Shelagh Manton: > I have some general questions about sound in linux; the interplay of > pulse/(esd) and gstreamer,jackd and alsa. > Let me state what I think I know. > Alsa provides the drivers that allow sound to be produced and also the > midi subsystem. <snip> > If you want > to use midi and audio together as in rosegarden, you need jackd because > that allows more than one program to access the soundcard at a time. It > is also useful because if you have the right kernel and privileges your > audio programme can override the right of other programmes to access the > kernel as well meaning that you don't get glitches when you are > recording a masterpiece. Well, not really. jackd is needed to have sound-exchange between apps. The hardware soundcards are kind of a special application to exchange sound with. And all the sound-exchange is sample-synced and it also provides a global transport to start, stop or generally position the playhead of all (supporting) apps in synchronization. The fact that the jack-lib also provides an easy way to get higher rights for the audio-thread is only a bonus and convenience. Each application programmer could do this himself for each app. And, jack is not overriding or modifying access to the kernel (you would need a kernel-module for that). It "just" provides an easy interface to gain more priority in the schedulers of the kernel. Normally only root(-processes) can get a higher priority than normal users (everyone can get a lower priority by themself). Different ways to authorize for gaining more priority exist, realtime-lsm and rt-limits are the keywords here. Jack just tries to get a higher priority without having every application programmer fiddle with this. > Gstreamer fits in the normal esd/pulse picture > by providing the access to codecs that files come in. Now this is where > my understanding fails: gstreamer has a jack module (so I hear rumoured, > but I can't find it in the ubuntu reps) and so does pulse. How do these > fit in with the jackd stuff? Obviously they both make it so that jack > can work with both or either of the sound servers. These modules do not make jack work with pulse/gstreamer. They make pulse/gstreamer work with jack. Its not jack outputing to these soundservers, the soundservers/systems are sending their audio to jack if you use these modules. Hope that helps, Arnold -- visit http://www.arnoldarts.de/ --- Hi, I am a .signature virus. Please copy me into your ~/.signature and send me to all your contacts. After a month or so log in as root and do a rm / -rf. Or ask your administrator to do so...
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