[SDL] Some sounds not played by SDL_mixer, but channels not exhausted
sarrazip at sympatico.ca
Wed Jan 8 17:14:00 PST 2003
A video game I am developing uses SDL_mixer (2.2.4) to produce sound
effects and sometimes, some sounds are not heard, even though there
are more than enough channels.
The program calls this statement:
Mix_PlayChannel(-1, sample, 0)
and if it returns -1, the string returned by Mix_GetError() is
thrown as a C++ exception (of type string). No such exception is
ever thrown by my program, so the failure does not seem to be there.
'sample' is loaded by Mix_LoadWAV().
The sound effects are heard correctly most of the time. However,
it seems like when two or three calls to Mix_PlayChannel() happen
too close to one another, one of the sounds is not played.
The sound system is initialized this way:
if (Mix_OpenAudio(11025, AUDIO_U8, 1, 256) == -1)
The game produces about 20 frames per second. When I coded two
consecutive calls to Mix_PlayChannel(), one of the sounds was not
played. Then I created a queue of sounds to be played, and coded a
system that played only one sound out of this queue at each frame.
With this system, both sounds were heard.
However, this hack does not work all the time. I still get
situations in the game where a sound effect should be played but
is not heard. Unfortunately, this is difficult to reproduce.
Adding some trace code has shown that at most 3 channels are used
at the same time in this game, so the missed sounds cannot be due
to a lack of available channels (I allocate 16). Mix_PlayChannel()
never returns -1 in these scenarios. It returns 0, 1 or 2.
Yet it seems like whenever a sound needs to play on channel 2
(because 0 and 1 are already playing a sound), the problem occurs.
My program links with SDL 1.2.4, SDL_image 1.2.2 and SDL_mixer 1.2.4.
It is compiled with g++ 2.96-112 on a RedHat 7.2 system.
The sound card is an Ensoniq 5880 AudioPCI according to /proc/pci.
If anyone has had a similar problem in the past, where should I
look for trouble?
Pierre Sarrazin <sarrazip at sympatico dot ca>
More information about the SDL