[pulseaudio-discuss] These ideas I've had for the better part of a month, forgive me for there length.

Tanu Kaskinen tanuk at iki.fi
Fri Aug 13 21:30:16 PDT 2010

On Sat, 2010-08-07 at 12:47 -0500, Mike Mestnik wrote:
> There is a cause to add several stream types to pulse audio for the
> support of all the hardware's features.  Current stream types can be
> described by ~3 dimensions (channels, bits, bit-format, rate).
> The first that would be necessary is raw.  That is pre-mixed information
> that can't be further mixed.  Each stream is to be given a priority
> ~0-15 where default for existing streams is 7 and raw streams default to 11.
> This makes pre-mixed sounds cause all other sounds to be silenced so
> they can be played.  The effect is the ability to play videos(ac3/dts)
> while other applications are emitting data, no need to close
> browser/flash.  The first optional extension is the ability to indicate
> to sources that they will not be played in the form of a warning
> returned to data passed and a signal indicating that play can continue.

I don't know if you've followed the recent AC3 discussion, but some
support for "raw" (aka passthrough) streams has been implemented now.
Currently the logic doesn't give precedence for passthrough streams. It
might make sense to do so, though.

> A notable improvement over the current ALSA-passthrough is the addition
> of framing.  Currently pausing and restarting a pre-mixed stream causes
> loud pops and clicks, this is undesirable and as such pulse audio can
> offer a solution.

The current code doesn't understand such frames, but I think this idea
is also a good one to keep in mind.

> The next stream type should be a pulse audio internal type(s) used for
> the mixing of mp3/ac3 and perhaps dts streams.  It's my understanding
> that ac3 uses vectors to describe 6 channels of sound much like a 2ch
> mp3.  If I'm not mistaken these vectors can be combined mathematically
> as-is to represent the combination of two sounds.  This would be a great
> achivement over any uncompress/combine/recompress senerio.

Do you have any pointers to how this is done? If it's true that there
really is a way to mix compressed streams without uncompressing first,
then maybe volume adjustment is possible too?

Tanu Kaskinen

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