[pulseaudio-discuss] [RFC] Dynamic reconfiguration of sampling rate

[Mark Brown]

On Mon, Jan 17, 2011 at 02:24:51PM -0600, pl bossart wrote:

> I can see cases where you have 1 compressed stream and 1 PCM, and you
> mix the two in hardware, but I am having a really hard time finding a
> use case where you would have multiple (more than 2) PCM streams at
> different rates. Maybe automotive cases, where the infotainment unit
> might send multiple streams to a head unit were the mixing/routing is
> actually done? Did anyone request hardware mixing on the mailing list?

Classic case is system sounds mixed in with media playback, and you also
get applications that decide they want to play multiple sources of their
own at once (games with music plus multiple game sounds are probably the
most complex example).

If you play a new message notification over a movie then if the
notification is an MP3 at 44.1kHz and the movie is at 48kHz you need SRC
as well as mixing, and even on a phone you may want to route things to
different sets of outputs simultaneously (eg, music to headphones and
ringtone to headphones plus speaker).  There's also the simple argument
that if your hardware is capable of offloading some of the DSP work from
the CPU more efficiently than the CPU can do it itself that's a win.