[LAD] mixing music and sound effects using libao

[Hermann Meyer]

Am 01.05.2015 um 00:17 schrieb dave at 661.org:
> On Thu, 30 Apr 2015, Hermann Meyer wrote:
>
>> Am 30.04.2015 um 10:41 schrieb dave at 661.org:
>>>
>>> I've been playing around with libsndfile, libvorbisfile, libmodplug, 
>>> and libao to provide background music and sound effects for a game 
>>> engine.  I have a solid handle on making one noise at a time, but I 
>>> don't understand mixing.  At first I thought I would have to write 
>>> my own mixer and handle the channels, sample rate, and sample size 
>>> issues myself.  I really don't want to have to do that.  Then I 
>>> noticed in the libao documentation that nothing says that I cannot 
>>> spawn two threads, each of which calls ao_open_live() and ao_play() 
>>> on different sound files.  Indeed, the docs for ao_initialize() seem 
>>> to suggest this can be done with the statement that it be called in 
>>> the main thread.
>>>
>>> I tried this and it works so erratically that I'm not sure libao was 
>>> written with this in mind.  I get these results in order of likelihood:
>>>
>>> 1) "Segmentation fault"
>>>
>>> 2) "*** glibc detected *** ./threadtest7: malloc(): memory corruption
>>>     (fast): 0x0000000001bc5390 *** Bus error"
>>>
>>> 3) "*** glibc detected *** ./threadtest7: double free or corruption 
>>> (out):
>>>     0x00000000018ba2e0 ***"
>>>
>>> 4) A bit of the first file, then the second file.
>>>
>>> 5) Only the second file.
>>>
>>> 6) Both files messily mixed with a zipping noise. (very rare)
>>>
>>> Is libao in fact intentionally capable of doing this?  If not, what 
>>> are my options for mixing music and sound effects?  I really don't 
>>> want to use SDL_mixer for a variety of reasons, chiefly because my 
>>> program is terminal-only.  Virtual beer if you can guess what the 
>>> program is.
>>
>> Hi
>>
>> It seems libao is able to do this. Attached is the example code from 
>> the libao side, roughly hacked in a second thread to play to signals 
>> simultaneous. Works stable here.
>
> This has trouble opening the second device:
>
> ALSA lib pcm_dmix.c:1018:(snd_pcm_dmix_open) unable to open slave
> Error opening device2.
>
> I'm using Debian Wheezy amd64 without Pulseaudio.  Maybe Debian's 
> default setup for ALSA is wrong?  There are no /etc/asound.conf or 
> ~/.asoundrc files.
>
>
Well, here is debian/sid with pulse/jack running. Indeed, it didn't work 
with plain ALSA, . .