Message: 2
Date: Sat, 14 Aug 2010 07:30:16 +0300
From: Tanu Kaskinen <ta...@iki.fi>
Subject: Re: [pulseaudio-discuss] These ideas I've had for the better
part of a month, forgive me for there length.
To: pulseaudio-discuss@mail.0pointer.de
Message-ID: <1281760216.5451.12.ca...@jarl>
Content-Type: text/plain; charset="UTF-8"
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?
I'm unsure of how this would work, but it'd be a lot of vector math.
Volume adjustment should be possible by setting DRC options and perhaps
other general volume tags. Adjusting the volume is difficult because it
would involve cos and tan plus vector math, if I understand the format
correctly.
What I was suggesting is a short-cut method to doing the full
uncompress/recompress. The result should be a playable stream that is
encoded using compression, but is likely not vary well compressed...
The resulting stream may well be bigger then it's uncompressed counterpart.
The idea being that space is less-precious then CPU time.
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