The state of the Linux/Unix application audio subsystems remains a mess of competing interfaces and audio mixer and networking demons. Proposal: Rationalizing Fedora Audio For Linux alone, there are many applications that still directly use the OSS interface, and will do so for the foreseeable future. Hacking the Fedora Core setup is more possible than fixing all the applications. There are a number of competing audio mixing demons that can be running by the user at the same time: Esound's esd, KDE's arts, and the Freedesktop's proposed MAS ( http://www.mediaapplicationserver.net/ ). The first two demons available on FC3 default to using the OSS /dev/dsp /dev/audio etc interfaces, competing for use of the /dev/dsp, hogging the audio output. Even using the ALSA interface, Fedora defaults to sending/receiving applications audio direct to the hardware device, hogging the interface. By default audio output could go to ALSA or better yet a Dmix plug, where the source and destination could be selected and mixed together. It's possible to get OSS, esd, arts and ALSA working together better with a little configuration... http://alsa.opensrc.org/index.php?page=Dmix+Kde+-+arts%2C+ESD+and+SDL+quick+and+dirty+HOWTO FC3 final, or the next release of Fedora Core/Red Hat after that, should do something similar in the default setup. The default pcm ALSA interface and /dev/dsp should be assigned to a type dmix. HAL/udev should assign hardware sound devices ALSA hw:X and OSS /dev/dspX etc ( with X starting at 1 not 0 see below ). By default the output from first dmix could be piped to the first or owner selected device. The user should also be provided with command line and GUI interfaces to HAL/udev add and remove dmix devices on the fly and select where the output goes to. The volume for each virtual device should be set at 50% by default. Virtual mixer interfaces would also be created by default, and the interface would show up in the gnome-audio-mixer. This would be great for recording content and for Multiuser systems. Future proposal : Multiuser/Mixcasting audio - /dev/dsp like /dev/tty At the moment LTSP and other remote-X servers use ESD,NAS and in the future MAS demons to stream audio over the network. If your the only user assigned to a /dev/dsp it is also sometimes possible to capture the output to OSS and directed to the sound demon. The major problem with this is that the first user to log on gain full ownership of the audio devices, sharing is difficult. One solution is to hack the kernel ALSA so that hw:0 and /dev/dsp are assigned on the fly depending on the UID of the process much the way /dev/tty is assigned on the fly to the caller process's current /dev/ttyX. HAL/udev could assign numbered dmix type ALSA devices to each user and and the sound demon would be free capture the output. Even for single user systems, you could use "Xnest -query :X" to log in as a different user and capture all the auto to stream it out or record it to a demo or audioblog. -- David Mohring <heretic@xxxxxxxxxx>
